diff --git a/app/(main)/assessment/AssessmentWorkspace.tsx b/app/(main)/assessment/AssessmentWorkspace.tsx
new file mode 100644
index 00000000..502403d4
--- /dev/null
+++ b/app/(main)/assessment/AssessmentWorkspace.tsx
@@ -0,0 +1,26 @@
+"use client";
+
+// Shared body for every /assessment sub-route. The route decides which tab is
+// active via `initialTab`; the page shell for each route just renders this.
+import { Suspense } from "react";
+import { Loader } from "@/app/components/ui";
+import PageLayout from "@/app/components/assessment/PageLayout";
+import { useAssessmentWorkflow } from "@/app/hooks/useAssessmentWorkflow";
+import type { AssessmentTabId } from "@/app/lib/types/assessment";
+
+function WorkspaceContent({ initialTab }: { initialTab: AssessmentTabId }) {
+  const layoutProps = useAssessmentWorkflow(initialTab);
+  return <PageLayout {...layoutProps} />;
+}
+
+export default function AssessmentWorkspace({
+  initialTab = "datasets",
+}: {
+  initialTab?: AssessmentTabId;
+}) {
+  return (
+    <Suspense fallback={<Loader size="lg" message="Loading..." fullScreen />}>
+      <WorkspaceContent initialTab={initialTab} />
+    </Suspense>
+  );
+}
diff --git a/app/(main)/assessment/[tab]/page.tsx b/app/(main)/assessment/[tab]/page.tsx
new file mode 100644
index 00000000..3c67a2ea
--- /dev/null
+++ b/app/(main)/assessment/[tab]/page.tsx
@@ -0,0 +1,14 @@
+"use client";
+
+import { notFound, useParams } from "next/navigation";
+import { ASSESSMENT_ROUTE_SEGMENT_TO_TAB } from "@/app/lib/assessment/constants";
+import AssessmentWorkspace from "../AssessmentWorkspace";
+
+// Sub-routes /assessment/config | /assessment/experiment | /assessment/runs.
+// Datasets lives at the base /assessment route.
+export default function AssessmentTabPage() {
+  const params = useParams<{ tab: string }>();
+  const tab = ASSESSMENT_ROUTE_SEGMENT_TO_TAB[params?.tab ?? ""];
+  if (!tab) notFound();
+  return <AssessmentWorkspace initialTab={tab} />;
+}
diff --git a/app/(main)/assessment/page.tsx b/app/(main)/assessment/page.tsx
index e8e295bb..ec1fb328 100644
--- a/app/(main)/assessment/page.tsx
+++ b/app/(main)/assessment/page.tsx
@@ -1,19 +1,5 @@
-"use client";
-
-import { Suspense } from "react";
-import { Loader } from "@/app/components/ui";
-import PageLayout from "@/app/components/assessment/PageLayout";
-import { useAssessmentWorkflow } from "@/app/hooks/useAssessmentWorkflow";
-
-function PageContent() {
-  const layoutProps = useAssessmentWorkflow();
-  return <PageLayout {...layoutProps} />;
-}
+import AssessmentWorkspace from "./AssessmentWorkspace";
 
 export default function Page() {
-  return (
-    <Suspense fallback={<Loader size="lg" message="Loading..." fullScreen />}>
-      <PageContent />
-    </Suspense>
-  );
+  return <AssessmentWorkspace initialTab="datasets" />;
 }
diff --git a/app/api/assessment/datasets/[dataset_id]/rows/route.ts b/app/api/assessment/datasets/[dataset_id]/rows/route.ts
new file mode 100644
index 00000000..0fdef8cb
--- /dev/null
+++ b/app/api/assessment/datasets/[dataset_id]/rows/route.ts
@@ -0,0 +1,18 @@
+import { NextRequest } from "next/server";
+import { proxyErrorResponse, proxyJsonResponse } from "@/app/api/_routeProxy";
+
+export async function GET(
+  request: NextRequest,
+  { params }: { params: Promise<{ dataset_id: string }> },
+) {
+  try {
+    const { dataset_id } = await params;
+    return await proxyJsonResponse(
+      request,
+      `/api/v1/assessment/datasets/${dataset_id}/rows`,
+      { method: "GET" },
+    );
+  } catch (error: unknown) {
+    return proxyErrorResponse("Assessment dataset rows proxy error:", error);
+  }
+}
diff --git a/app/components/Sidebar.tsx b/app/components/Sidebar.tsx
index 6cc7d447..cec786f2 100644
--- a/app/components/Sidebar.tsx
+++ b/app/components/Sidebar.tsx
@@ -42,6 +42,7 @@ export default function Sidebar({
   const [expandedMenus, setExpandedMenus] = useState<Record<string, boolean>>({
     Evaluations: true,
     Configurations: false,
+    Assessment: true,
   });
   const [showLoginModal, setShowLoginModal] = useState(false);
   const [showUserMenu, setShowUserMenu] = useState(false);
diff --git a/app/components/assessment/AssessmentChildRunCard.tsx b/app/components/assessment/AssessmentChildRunCard.tsx
index 2faa07d1..c2ce4cb3 100644
--- a/app/components/assessment/AssessmentChildRunCard.tsx
+++ b/app/components/assessment/AssessmentChildRunCard.tsx
@@ -126,6 +126,21 @@ export default function AssessmentChildRunCard({
               </div>
             )}
 
+            {childRun.cost && (
+              <div className="mt-1.5 text-xs text-text-secondary">
+                Cost:{" "}
+                <span className="font-medium text-text-primary">
+                  ${childRun.cost.total.toFixed(4)}
+                </span>
+                {childRun.cost.pre_filter && (
+                  <span className="ml-1">
+                    · assessment ${childRun.cost.assessment.toFixed(4)} ·
+                    pre-filter ${childRun.cost.pre_filter.total.toFixed(4)}
+                  </span>
+                )}
+              </div>
+            )}
+
             <ChildRunStageProgress stages={stageProgress} />
 
             {configError && (
diff --git a/app/components/assessment/ColumnMapperStep.tsx b/app/components/assessment/ColumnMapperStep.tsx
index fd29e869..79a406df 100644
--- a/app/components/assessment/ColumnMapperStep.tsx
+++ b/app/components/assessment/ColumnMapperStep.tsx
@@ -1,144 +1,121 @@
 "use client";
 
-import { useEffect, useState } from "react";
+import { useEffect, useRef, useState } from "react";
 import { Button, Select } from "@/app/components/ui";
-import {
-  ASSESSMENT_ROLE_OPTION_MAP,
-  ASSESSMENT_ROLE_OPTIONS,
-  ATTACHMENT_FORMATS,
-} from "@/app/lib/assessment/constants";
+import { TrashIcon } from "@/app/components/icons";
 import type {
   Attachment,
-  ColumnConfig,
-  ColumnRole,
+  ColumnMapping,
   ColumnMapperStepProps,
 } from "@/app/lib/types/assessment";
-import { buildColumnConfigs, colorMapping } from "@/app/lib/utils/assessment";
+import type { AssessmentColumnType } from "@/app/lib/types/configs";
+
+interface InputField {
+  id: string;
+  name: string;
+  type: AssessmentColumnType;
+  strict: boolean;
+}
+
+const INPUT_TYPE_OPTIONS: Array<{
+  value: AssessmentColumnType;
+  label: string;
+}> = [
+  { value: "text", label: "Text" },
+  { value: "image", label: "Image" },
+  { value: "pdf", label: "PDF" },
+];
+
+const STRICT_OPTIONS = [
+  { value: "false", label: "Optional" },
+  { value: "true", label: "Required" },
+];
+
+function toFields(mapping: ColumnMapping): InputField[] {
+  const strictColumns = new Set(mapping.strictColumns ?? []);
+  const textFields = mapping.textColumns.map((name, index) => ({
+    id: `t${index}`,
+    name,
+    type: "text" as AssessmentColumnType,
+    strict: strictColumns.has(name),
+  }));
+  const attachmentFields = mapping.attachments.map((attachment, index) => ({
+    id: `a${index}`,
+    name: attachment.column,
+    type: (attachment.type === "pdf" ? "pdf" : "image") as AssessmentColumnType,
+    strict: strictColumns.has(attachment.column),
+  }));
+  return [...textFields, ...attachmentFields];
+}
+
+// Serialize the manual field list back into the ColumnMapping shape that
+// buildAssessmentInputSchema already understands (text -> input, image/pdf ->
+// attachment with format "url"); strict column names are collected separately.
+function toMapping(fields: InputField[]): ColumnMapping {
+  const textColumns: string[] = [];
+  const attachments: Attachment[] = [];
+  const strictColumns: string[] = [];
+  for (const field of fields) {
+    const name = field.name.trim();
+    if (!name) continue;
+    if (field.type === "text") {
+      textColumns.push(name);
+    } else {
+      attachments.push({ column: name, type: field.type, format: "url" });
+    }
+    if (field.strict) strictColumns.push(name);
+  }
+  return { textColumns, attachments, groundTruthColumns: [], strictColumns };
+}
 
 export default function ColumnMapperStep({
-  columns,
   columnMapping,
   setColumnMapping,
   onNext,
-  onBack,
+  syncToken,
 }: ColumnMapperStepProps) {
-  const [columnConfigs, setColumnConfigs] = useState<ColumnConfig[]>(() =>
-    buildColumnConfigs(columns, columnMapping),
+  const [fields, setFields] = useState<InputField[]>(() =>
+    toFields(columnMapping),
   );
+  const nextId = useRef(0);
 
+  // Re-seed the local field list from the mapping whenever a config is
+  // (re)loaded. Keyed on syncToken only (not columnMapping) so ongoing edits —
+  // which flow local -> columnMapping via commit() — are never clobbered.
+  const mappingRef = useRef(columnMapping);
   useEffect(() => {
-    setColumnConfigs(buildColumnConfigs(columns, columnMapping));
-  }, [columns, columnMapping]);
-
-  const updateRole = (index: number, role: ColumnRole) => {
-    if (role === "ground_truth") {
+    mappingRef.current = columnMapping;
+  });
+  const isFirstSyncRef = useRef(true);
+  useEffect(() => {
+    if (isFirstSyncRef.current) {
+      isFirstSyncRef.current = false;
       return;
     }
+    setFields(toFields(mappingRef.current));
+  }, [syncToken]);
 
-    setColumnConfigs((prev) => {
-      const current = prev[index];
-      const next = [...prev];
-
-      if (role !== "attachment") {
-        next[index] = { role };
-        return next;
-      }
-
-      next[index] = {
-        role,
-        attachmentType: current?.attachmentType || "mixed",
-        attachmentFormat: current?.attachmentFormat || "url",
-      };
-      return next;
-    });
+  const commit = (updated: InputField[]) => {
+    setFields(updated);
+    setColumnMapping(toMapping(updated));
   };
 
-  const updateAttachmentType = (
-    index: number,
-    type: "image" | "pdf" | "mixed",
-  ) => {
-    setColumnConfigs((prev) => {
-      const next = [...prev];
-      next[index] = {
-        ...prev[index],
-        role: "attachment",
-        attachmentType: type,
-        attachmentFormat: "url",
-      };
-      return next;
-    });
-  };
-
-  const updateAttachmentFormat = (index: number, format: string) => {
-    setColumnConfigs((prev) => {
-      const next = [...prev];
-      next[index] = {
-        ...prev[index],
-        role: "attachment",
-        attachmentFormat: format,
-      };
-      return next;
-    });
-  };
-
-  const patchAttachment = (index: number, patch: Partial<ColumnConfig>) => {
-    setColumnConfigs((prev) => {
-      const next = [...prev];
-      next[index] = { ...prev[index], role: "attachment", ...patch };
-      return next;
-    });
-  };
+  const addField = () =>
+    commit([
+      ...fields,
+      { id: `f${nextId.current++}`, name: "", type: "text", strict: false },
+    ]);
 
-  const handleNext = () => {
-    const textColumns: string[] = [];
-    const attachments: Attachment[] = [];
+  const updateField = (id: string, patch: Partial<InputField>) =>
+    commit(
+      fields.map((field) => (field.id === id ? { ...field, ...patch } : field)),
+    );
 
-    columnConfigs.forEach((config, index) => {
-      const column = columns[index];
-      if (!column) return;
+  const removeField = (id: string) =>
+    commit(fields.filter((field) => field.id !== id));
 
-      if (config.role === "text") {
-        textColumns.push(column);
-      } else if (
-        config.role === "attachment" &&
-        config.attachmentType &&
-        config.attachmentFormat
-      ) {
-        const attachment: Attachment = {
-          column,
-          type: config.attachmentType,
-          format: config.attachmentFormat as Attachment["format"],
-        };
-        if (config.attachmentType === "mixed" && config.attachmentTypeColumn) {
-          const map: Record<string, string> = {};
-          const split = (s?: string) =>
-            (s || "")
-              .split(",")
-              .map((v) => v.trim())
-              .filter(Boolean);
-          split(config.attachmentImageValues).forEach(
-            (v) => (map[v] = "image"),
-          );
-          split(config.attachmentPdfValues).forEach((v) => (map[v] = "pdf"));
-          if (Object.keys(map).length > 0) {
-            attachment.type_column = config.attachmentTypeColumn;
-            attachment.type_value_map = map;
-          }
-        }
-        attachments.push(attachment);
-      }
-    });
-
-    setColumnMapping({ textColumns, attachments, groundTruthColumns: [] });
-    onNext();
-  };
-
-  const mappedCount = columnConfigs.filter(
-    (config) => config.role !== "unmapped",
-  ).length;
-  const hasMappedColumn = columnConfigs.some(
-    (config) => config.role === "text" || config.role === "attachment",
-  );
+  const namedCount = fields.filter((field) => field.name.trim()).length;
+  const hasField = namedCount > 0;
 
   return (
     <div className="flex h-full min-h-0 w-full flex-col">
@@ -146,254 +123,132 @@ export default function ColumnMapperStep({
         <div className="flex items-start justify-between gap-4">
           <div>
             <h2 className="text-lg font-semibold text-text-primary">
-              Map Columns
+              Input Schema
             </h2>
             <p className="mt-1 text-sm text-text-secondary">
-              Choose a role for each column.
+              Define the input fields this configuration expects. Field names
+              are referenced in the prompt as{" "}
+              <code className="rounded bg-bg-secondary px-1 text-[11px]">
+                {"{field_name}"}
+              </code>
+              . No dataset needed.
             </p>
           </div>
           <div className="rounded-full bg-bg-secondary px-3 py-1 text-xs font-medium text-text-secondary">
-            {mappedCount}/{columns.length} mapped
+            {namedCount} field{namedCount === 1 ? "" : "s"}
           </div>
         </div>
 
-        {columns.length === 0 ? (
-          <div className="rounded-2xl border border-border bg-bg-primary px-6 py-10 text-center">
-            <p className="text-sm font-medium text-text-primary">
-              No columns found.
-            </p>
-            <p className="mt-1 text-sm text-text-secondary">
-              Go back and select a dataset first.
-            </p>
-          </div>
-        ) : (
-          <div className="overflow-hidden rounded-2xl border border-border bg-bg-primary">
-            {columns.map((column, index) => {
-              const config = columnConfigs[index] || {
-                role: "unmapped" as ColumnRole,
-              };
-              const activeOption =
-                ASSESSMENT_ROLE_OPTION_MAP[config.role] ||
-                ASSESSMENT_ROLE_OPTION_MAP.unmapped;
-              const roleVisuals = colorMapping(activeOption.value);
-
-              return (
-                <div
-                  key={index}
-                  className={`bg-bg-primary px-4 py-4 sm:px-5 ${
-                    index === 0 ? "" : "border-t border-border"
-                  }`}
-                >
-                  <div
-                    className={`flex flex-col gap-3 rounded-xl border px-3 py-3 ${roleVisuals.panelClass}`}
-                  >
-                    <div className="flex flex-col gap-3 sm:flex-row sm:items-start sm:justify-between">
-                      <div className="min-w-0 flex-1 sm:max-w-[50%]">
-                        <div className="flex items-start gap-2">
-                          <span
-                            className={`mt-1.5 h-2 w-2 shrink-0 rounded-full ${roleVisuals.dotClass}`}
-                          />
-                          <span className="min-w-0 wrap-break-word font-mono text-sm font-semibold text-text-primary">
-                            {column}
-                          </span>
-                        </div>
-                      </div>
-
-                      <div className="flex flex-wrap gap-2 sm:shrink-0">
-                        {ASSESSMENT_ROLE_OPTIONS.map((option) => {
-                          const isGroundTruth = option.value === "ground_truth";
-                          const isActive = config.role === option.value;
-                          return (
-                            <Button
-                              key={option.value}
-                              type="button"
-                              variant={isGroundTruth ? "ghost" : "outline"}
-                              size="sm"
-                              onClick={() => {
-                                if (!isGroundTruth) {
-                                  updateRole(index, option.value);
-                                }
-                              }}
-                              aria-disabled={isGroundTruth}
-                              title={
-                                isGroundTruth
-                                  ? "Ground Truth mapping is coming soon"
-                                  : undefined
-                              }
-                              className={`${
-                                isGroundTruth
-                                  ? "cursor-not-allowed! bg-transparent! hover:bg-transparent! text-text-secondary!"
-                                  : isActive
-                                    ? roleVisuals.activeButtonClass
-                                    : "bg-bg-primary! hover:bg-bg-secondary!"
-                              }`}
-                            >
-                              <span>{option.label}</span>
-                              {isGroundTruth && (
-                                <span className="rounded-full bg-bg-secondary px-1.5 py-0.5 text-[10px] font-medium text-text-secondary">
-                                  Soon
-                                </span>
-                              )}
-                            </Button>
-                          );
-                        })}
-                      </div>
+        <div className="space-y-3">
+          {fields.length === 0 ? (
+            <div className="rounded-2xl border border-dashed border-border bg-bg-primary px-6 py-10 text-center">
+              <p className="text-sm font-medium text-text-primary">
+                No input fields yet
+              </p>
+              <p className="mt-1 text-xs text-text-secondary">
+                Add the fields your assessment reads, then reference them in the
+                prompt as{" "}
+                <code className="rounded bg-bg-secondary px-1 text-[11px]">
+                  {"{field_name}"}
+                </code>
+                .
+              </p>
+            </div>
+          ) : (
+            <div className="overflow-hidden rounded-2xl border border-border bg-bg-primary">
+              <div className="grid grid-cols-[minmax(0,1fr)_120px_96px_120px_40px] gap-3 border-b border-border bg-bg-secondary px-4 py-2.5 text-[11px] font-semibold uppercase tracking-wider text-text-secondary">
+                <span>Field name</span>
+                <span>Type</span>
+                <span>Format</span>
+                <span>Required</span>
+                <span />
+              </div>
+              <div className="divide-y divide-border">
+                {fields.map((field) => {
+                  const isAttachment = field.type !== "text";
+                  return (
+                    <div
+                      key={field.id}
+                      className="grid grid-cols-[minmax(0,1fr)_120px_96px_120px_40px] items-center gap-3 px-4 py-2.5"
+                    >
+                      <input
+                        type="text"
+                        value={field.name}
+                        onChange={(event) =>
+                          updateField(field.id, { name: event.target.value })
+                        }
+                        placeholder="field name"
+                        className="h-9 min-w-0 rounded-lg border border-border bg-bg-primary px-3 text-sm text-text-primary outline-none focus:ring-1"
+                      />
+                      <Select
+                        value={field.type}
+                        onChange={(event) =>
+                          updateField(field.id, {
+                            type: event.target.value as AssessmentColumnType,
+                          })
+                        }
+                        options={INPUT_TYPE_OPTIONS}
+                        className="h-9 w-full cursor-pointer rounded-lg border border-border bg-bg-primary px-2.5 py-1.5 text-sm text-text-primary outline-none focus:ring-1"
+                      />
+                      {isAttachment ? (
+                        <span className="inline-flex items-center justify-center rounded-full bg-bg-secondary px-2 py-0.5 font-mono text-[11px] text-text-secondary">
+                          url
+                        </span>
+                      ) : (
+                        <span className="text-center text-xs text-text-secondary">
+                          —
+                        </span>
+                      )}
+                      <Select
+                        value={field.strict ? "true" : "false"}
+                        onChange={(event) =>
+                          updateField(field.id, {
+                            strict: event.target.value === "true",
+                          })
+                        }
+                        options={STRICT_OPTIONS}
+                        className="h-9 w-full cursor-pointer rounded-lg border border-border bg-bg-primary px-2.5 py-1.5 text-sm text-text-primary outline-none focus:ring-1"
+                      />
+                      <button
+                        type="button"
+                        onClick={() => removeField(field.id)}
+                        className="flex h-8 w-8 cursor-pointer items-center justify-center justify-self-center rounded-md text-text-secondary transition-colors hover:bg-status-error-bg hover:text-status-error-text"
+                        aria-label={`Delete ${field.name.trim() || "field"}`}
+                        title="Delete"
+                      >
+                        <TrashIcon className="w-4 h-4" />
+                      </button>
                     </div>
+                  );
+                })}
+              </div>
+            </div>
+          )}
 
-                    {config.role === "attachment" && (
-                      <>
-                        <div className="flex flex-col gap-3 pt-1 sm:flex-row">
-                          <label className="flex-1">
-                            <span className="mb-1 block text-xs font-medium text-text-secondary">
-                              Attachment Type
-                            </span>
-                            <Select
-                              value={config.attachmentType || "mixed"}
-                              onChange={(event) =>
-                                updateAttachmentType(
-                                  index,
-                                  event.target.value as
-                                    | "image"
-                                    | "pdf"
-                                    | "mixed",
-                                )
-                              }
-                              options={[
-                                {
-                                  value: "mixed",
-                                  label: "Mixed (image or PDF)",
-                                },
-                                { value: "image", label: "Image" },
-                                { value: "pdf", label: "PDF" },
-                              ]}
-                              className="w-full cursor-pointer rounded-lg border border-border bg-bg-primary px-3 py-2 text-sm text-text-primary outline-none focus:ring-1"
-                            />
-                          </label>
-
-                          <label className="flex-1">
-                            <span className="mb-1 block text-xs font-medium text-text-secondary">
-                              Source
-                            </span>
-                            <Select
-                              value={config.attachmentFormat || "url"}
-                              onChange={(event) =>
-                                updateAttachmentFormat(
-                                  index,
-                                  event.target.value,
-                                )
-                              }
-                              options={ATTACHMENT_FORMATS[
-                                config.attachmentType || "mixed"
-                              ].map((format) => ({
-                                value: format,
-                                label: format,
-                              }))}
-                              className="w-full cursor-pointer rounded-lg border border-border bg-bg-primary px-3 py-2 text-sm text-text-primary outline-none focus:ring-1"
-                            />
-                          </label>
-                        </div>
-
-                        {(config.attachmentType || "mixed") === "mixed" && (
-                          <div className="mt-2 flex flex-col gap-2 rounded-lg border border-border bg-bg-primary/50 p-3">
-                            <span className="text-[11px] text-text-secondary">
-                              Mixed: pick a column whose value tells each
-                              row&apos;s type, then list which values mean image
-                              vs PDF.
-                            </span>
-                            <label className="block">
-                              <span className="mb-1 block text-xs font-medium text-text-secondary">
-                                Type column
-                              </span>
-                              <Select
-                                value={config.attachmentTypeColumn || ""}
-                                onChange={(event) =>
-                                  patchAttachment(index, {
-                                    attachmentTypeColumn:
-                                      event.target.value || undefined,
-                                  })
-                                }
-                                options={[
-                                  { value: "", label: "Select column…" },
-                                  ...columns
-                                    .filter((_, i) => i !== index)
-                                    .map((col) => ({ value: col, label: col })),
-                                ]}
-                                className="w-full cursor-pointer rounded-lg border border-border bg-bg-primary px-3 py-2 text-sm text-text-primary outline-none focus:ring-1"
-                              />
-                            </label>
-                            {config.attachmentTypeColumn && (
-                              <div className="flex flex-col gap-2 sm:flex-row">
-                                <label className="flex-1">
-                                  <span className="mb-1 block text-xs font-medium text-text-secondary">
-                                    Values meaning Image
-                                  </span>
-                                  <input
-                                    type="text"
-                                    value={config.attachmentImageValues || ""}
-                                    onChange={(event) =>
-                                      patchAttachment(index, {
-                                        attachmentImageValues:
-                                          event.target.value,
-                                      })
-                                    }
-                                    placeholder="e.g. image, photo, jpg"
-                                    className="w-full rounded-lg border border-border bg-bg-primary px-3 py-2 text-sm text-text-primary outline-none focus:ring-1"
-                                  />
-                                </label>
-                                <label className="flex-1">
-                                  <span className="mb-1 block text-xs font-medium text-text-secondary">
-                                    Values meaning PDF
-                                  </span>
-                                  <input
-                                    type="text"
-                                    value={config.attachmentPdfValues || ""}
-                                    onChange={(event) =>
-                                      patchAttachment(index, {
-                                        attachmentPdfValues: event.target.value,
-                                      })
-                                    }
-                                    placeholder="e.g. pdf, document, doc"
-                                    className="w-full rounded-lg border border-border bg-bg-primary px-3 py-2 text-sm text-text-primary outline-none focus:ring-1"
-                                  />
-                                </label>
-                              </div>
-                            )}
-                          </div>
-                        )}
-                      </>
-                    )}
-                  </div>
-                </div>
-              );
-            })}
-          </div>
-        )}
+          <Button
+            type="button"
+            variant="outline"
+            size="sm"
+            onClick={addField}
+            className="w-full !justify-center !rounded-xl !border-dashed !py-2.5 text-text-primary"
+          >
+            + Add field
+          </Button>
+        </div>
       </div>
 
       <div className="mt-auto sticky bottom-0 z-10 -mx-6 flex flex-col gap-3 border-t border-border bg-bg-secondary px-6 py-3 sm:flex-row sm:items-center sm:justify-between">
-        <div className="mx-auto flex w-full max-w-5xl flex-col gap-3 sm:flex-row sm:items-center sm:justify-between">
-          <Button type="button" variant="outline" onClick={onBack}>
-            Back
+        <div className="mx-auto flex w-full max-w-5xl items-center justify-end gap-3">
+          <span
+            className={`text-xs ${
+              hasField ? "text-text-secondary" : "text-status-warning"
+            }`}
+          >
+            {hasField ? "Ready to continue." : "Add at least one input field."}
+          </span>
+          <Button type="button" onClick={onNext} disabled={!hasField}>
+            Next: Pre-filter
           </Button>
-
-          <div className="flex flex-col gap-3 sm:flex-row sm:items-center">
-            <span
-              className={`text-xs ${
-                hasMappedColumn ? "text-text-secondary" : "text-status-warning"
-              }`}
-            >
-              {hasMappedColumn
-                ? "Ready to continue."
-                : "Map at least one Text or Attachment column."}
-            </span>
-            <Button
-              type="button"
-              onClick={handleNext}
-              disabled={!hasMappedColumn}
-            >
-              Next: Eliminatory
-            </Button>
-          </div>
         </div>
       </div>
     </div>
diff --git a/app/components/assessment/ConfigPanel.tsx b/app/components/assessment/ConfigPanel.tsx
index ad3edabe..3f719d8d 100644
--- a/app/components/assessment/ConfigPanel.tsx
+++ b/app/components/assessment/ConfigPanel.tsx
@@ -1,67 +1,35 @@
 "use client";
 
-import { Button } from "@/app/components/ui";
-import { DatabaseIcon } from "@/app/components/icons";
 import { ASSESSMENT_CONFIG_STEPS } from "@/app/lib/assessment/constants";
 import type { ConfigPanelProps } from "@/app/lib/types/assessment";
 import ColumnMapperStep from "./ColumnMapperStep";
+import ConfigSelectStep from "./ConfigSelectStep";
 import PrefilterStep from "./PrefilterStep";
-import PostProcessingStep from "./PostProcessingStep";
 import PromptAndConfigStep from "./PromptAndConfigStep";
-import ReviewStep from "./ReviewStep";
 import Stepper from "./Stepper";
 
 export default function ConfigPanel({
-  canSubmitAssessment,
-  columns,
   columnMapping,
   completedSteps,
   configStep,
   configs,
-  datasetId,
-  experimentName,
-  formState,
-  hasDataset,
-  isSubmitting,
   prefilterConfig,
   outputSchema,
   systemInstruction,
   promptTemplate,
-  postProcessingConfig,
-  setPostProcessingConfig,
-  sampleRow,
-  setActiveTabToDatasets,
   setColumnMapping,
   setConfigStep,
   setConfigs,
-  setExperimentName,
   setPrefilterConfig,
   setOutputSchema,
   setSystemInstruction,
   setPromptTemplate,
-  submitBlockerMessage,
-  onSubmit,
   onStepComplete,
+  configSeed,
+  onStartNewConfig,
+  onLoadExistingConfig,
+  onForbidden,
 }: ConfigPanelProps) {
-  if (!hasDataset) {
-    return (
-      <div className="flex-1 flex items-center justify-center">
-        <div className="text-center">
-          <DatabaseIcon className="mx-auto mb-4 h-12 w-12 text-border" />
-          <p className="mb-1 text-sm font-medium text-text-primary">
-            No dataset selected
-          </p>
-          <p className="mb-4 text-xs text-text-secondary">
-            Select a dataset first from the Datasets tab
-          </p>
-          <Button type="button" onClick={setActiveTabToDatasets}>
-            Go to Datasets
-          </Button>
-        </div>
-      </div>
-    );
-  }
-
   return (
     <>
       <Stepper
@@ -75,40 +43,51 @@ export default function ConfigPanel({
           className={
             configStep === 1 ? "flex min-h-0 h-full flex-1 flex-col" : "hidden"
           }
+        >
+          <ConfigSelectStep
+            onStartNew={onStartNewConfig}
+            onLoadExisting={onLoadExistingConfig}
+            onForbidden={onForbidden}
+            onNext={() => onStepComplete(1)}
+          />
+        </div>
+
+        <div
+          className={
+            configStep === 2 ? "flex min-h-0 h-full flex-1 flex-col" : "hidden"
+          }
         >
           <ColumnMapperStep
-            columns={columns}
             columnMapping={columnMapping}
             setColumnMapping={setColumnMapping}
-            onNext={() => onStepComplete(1)}
-            onBack={setActiveTabToDatasets}
+            onNext={() => onStepComplete(2)}
+            syncToken={configSeed?.nonce}
           />
         </div>
 
         <div
           className={
-            configStep === 2 ? "flex min-h-0 h-full flex-1 flex-col" : "hidden"
+            configStep === 3 ? "flex min-h-0 h-full flex-1 flex-col" : "hidden"
           }
         >
           <PrefilterStep
-            key={datasetId ?? "no-dataset"}
             columns={columnMapping.textColumns}
             attachmentColumns={columnMapping.attachments.map((a) => a.column)}
             prefilterConfig={prefilterConfig}
             setPrefilterConfig={setPrefilterConfig}
-            onNext={() => onStepComplete(2)}
-            onBack={() => setConfigStep(1)}
+            onNext={() => onStepComplete(3)}
+            onBack={() => setConfigStep(2)}
+            syncToken={configSeed?.nonce}
           />
         </div>
 
         <div
           className={
-            configStep === 3 ? "flex min-h-0 h-full flex-1 flex-col" : "hidden"
+            configStep === 4 ? "flex min-h-0 h-full flex-1 flex-col" : "hidden"
           }
         >
           <PromptAndConfigStep
             textColumns={columnMapping.textColumns}
-            sampleRow={sampleRow}
             systemInstruction={systemInstruction}
             setSystemInstruction={setSystemInstruction}
             promptTemplate={promptTemplate}
@@ -117,43 +96,13 @@ export default function ConfigPanel({
             setConfigs={setConfigs}
             outputSchema={outputSchema}
             setOutputSchema={setOutputSchema}
-            onNext={() => onStepComplete(3)}
-            onBack={() => setConfigStep(2)}
-          />
-        </div>
-
-        <div
-          className={
-            configStep === 4 ? "flex min-h-0 h-full flex-1 flex-col" : "hidden"
-          }
-        >
-          <PostProcessingStep
-            postProcessingConfig={postProcessingConfig}
-            setPostProcessingConfig={setPostProcessingConfig}
             columnMapping={columnMapping}
-            outputSchema={outputSchema}
+            prefilterConfig={prefilterConfig}
+            configSeed={configSeed}
             onNext={() => onStepComplete(4)}
             onBack={() => setConfigStep(3)}
           />
         </div>
-
-        <div
-          className={
-            configStep === 5 ? "flex min-h-0 h-full flex-1 flex-col" : "hidden"
-          }
-        >
-          <ReviewStep
-            formState={formState}
-            experimentName={experimentName}
-            setExperimentName={setExperimentName}
-            isSubmitting={isSubmitting}
-            canSubmit={canSubmitAssessment}
-            submitBlockerMessage={submitBlockerMessage}
-            onSubmit={onSubmit}
-            onBack={() => setConfigStep(4)}
-            onEditStep={setConfigStep}
-          />
-        </div>
       </div>
     </>
   );
diff --git a/app/components/assessment/ConfigSelectStep.tsx b/app/components/assessment/ConfigSelectStep.tsx
new file mode 100644
index 00000000..e53f63ae
--- /dev/null
+++ b/app/components/assessment/ConfigSelectStep.tsx
@@ -0,0 +1,302 @@
+"use client";
+
+import { useEffect, useMemo, useState } from "react";
+import { Button, Loader } from "@/app/components/ui";
+import { VersionPill } from "@/app/components";
+import {
+  ChevronDownIcon,
+  PlusIcon,
+  RefreshIcon,
+  SearchIcon,
+} from "@/app/components/icons";
+import { useAuth } from "@/app/lib/context/AuthContext";
+import { useToast } from "@/app/hooks/useToast";
+import {
+  fetchConfigPage,
+  fetchConfigVersionDetail,
+  fetchConfigVersionsPage,
+} from "@/app/lib/utils/assessmentFetcher";
+import { handleForbiddenError } from "@/app/lib/utils/assessment";
+import { formatRelativeTime } from "@/app/lib/utils";
+import type { ConfigSelectStepProps } from "@/app/lib/types/assessment";
+import type {
+  AssessmentConfigBlob,
+  ConfigPublic,
+  ConfigVersionItems,
+} from "@/app/lib/types/configs";
+
+interface ConfigSelectCardProps {
+  config: ConfigPublic;
+  apiKey: string;
+  tag: string;
+  isLoadingId: string | null;
+  onPick: (config: ConfigPublic, version: number) => void;
+}
+
+function ConfigSelectCard({
+  config,
+  apiKey,
+  tag,
+  isLoadingId,
+  onPick,
+}: ConfigSelectCardProps) {
+  const toast = useToast();
+  const [expanded, setExpanded] = useState(false);
+  const [versions, setVersions] = useState<ConfigVersionItems[] | null>(null);
+  const [isLoadingVersions, setIsLoadingVersions] = useState(false);
+
+  const toggle = async () => {
+    if (expanded) {
+      setExpanded(false);
+      return;
+    }
+    setExpanded(true);
+    if (versions) return;
+    setIsLoadingVersions(true);
+    try {
+      const page = await fetchConfigVersionsPage(apiKey, config.id, {
+        limit: 100,
+        tag,
+      });
+      setVersions(page.items);
+    } catch (err) {
+      toast.error(
+        err instanceof Error ? err.message : "Failed to load versions",
+      );
+    } finally {
+      setIsLoadingVersions(false);
+    }
+  };
+
+  return (
+    <div
+      className={`rounded-lg bg-bg-primary transition-all min-w-0 ${
+        expanded
+          ? "shadow-[0_2px_12px_rgba(0,0,0,0.06)]"
+          : "shadow-[0_1px_3px_rgba(0,0,0,0.04)] hover:shadow-[0_2px_8px_rgba(0,0,0,0.06)]"
+      }`}
+    >
+      <button
+        type="button"
+        onClick={() => void toggle()}
+        className="w-full px-5 py-3 text-left"
+        aria-expanded={expanded}
+      >
+        <div className="flex items-start justify-between gap-3">
+          <div className="min-w-0 flex-1">
+            <h3 className="truncate text-sm font-semibold text-text-primary">
+              {config.name}
+            </h3>
+            {config.description && (
+              <p className="mt-0.5 truncate text-sm text-text-secondary">
+                {config.description}
+              </p>
+            )}
+            <p className="mt-2 text-xs text-text-secondary">
+              Updated {formatRelativeTime(config.updated_at)}
+            </p>
+          </div>
+          <ChevronDownIcon
+            className={`h-4 w-4 shrink-0 text-text-secondary transition-transform ${
+              expanded ? "rotate-180" : ""
+            }`}
+          />
+        </div>
+      </button>
+
+      {expanded && (
+        <div className="border-t border-neutral-100 px-4 py-3">
+          {isLoadingVersions ? (
+            <Loader size="sm" message="Loading versions..." />
+          ) : versions && versions.length > 0 ? (
+            <ul className="space-y-1.5">
+              {versions.map((item) => {
+                const loadingKey = `${config.id}:${item.version}`;
+                return (
+                  <li key={item.id}>
+                    <button
+                      type="button"
+                      onClick={() => onPick(config, item.version)}
+                      disabled={isLoadingId !== null}
+                      className="flex w-full items-center gap-2 rounded-md px-2 py-1.5 text-left transition-colors hover:bg-bg-secondary disabled:opacity-60"
+                    >
+                      <VersionPill version={item.version} size="sm" />
+                      <span className="min-w-0 flex-1 truncate text-sm text-text-primary">
+                        {item.commit_message || "No message"}
+                      </span>
+                      {isLoadingId === loadingKey ? (
+                        <span className="text-xs text-text-secondary">
+                          Loading…
+                        </span>
+                      ) : (
+                        <span className="text-xs font-medium text-accent-primary">
+                          Load
+                        </span>
+                      )}
+                    </button>
+                  </li>
+                );
+              })}
+            </ul>
+          ) : (
+            <p className="py-2 text-center text-xs text-text-secondary">
+              No versions found
+            </p>
+          )}
+        </div>
+      )}
+    </div>
+  );
+}
+
+export default function ConfigSelectStep({
+  onStartNew,
+  onLoadExisting,
+  onForbidden,
+  onNext,
+  tag = "ASSESSMENT",
+}: ConfigSelectStepProps) {
+  const { activeKey, isAuthenticated } = useAuth();
+  const apiKey = activeKey?.key ?? "";
+  const toast = useToast();
+
+  const [configs, setConfigs] = useState<ConfigPublic[]>([]);
+  const [isLoading, setIsLoading] = useState(false);
+  const [search, setSearch] = useState("");
+  const [loadingVersionKey, setLoadingVersionKey] = useState<string | null>(
+    null,
+  );
+
+  const loadConfigs = () => {
+    if (!isAuthenticated) return;
+    setIsLoading(true);
+    fetchConfigPage({ apiKey, limit: 100, tag })
+      .then((page) => setConfigs(page.items))
+      .catch((err) => {
+        if (err instanceof Error && handleForbiddenError(err, onForbidden)) {
+          return;
+        }
+        toast.error(
+          err instanceof Error ? err.message : "Failed to load configurations",
+        );
+      })
+      .finally(() => setIsLoading(false));
+  };
+
+  useEffect(() => {
+    if (!isAuthenticated) return;
+    loadConfigs();
+     
+  }, [isAuthenticated, apiKey, tag]);
+
+  const filtered = useMemo(() => {
+    // The scope is enforced by the `tag` query param on the fetch.
+    const query = search.trim().toLowerCase();
+    if (!query) return configs;
+    return configs.filter((config) =>
+      config.name.toLowerCase().includes(query),
+    );
+  }, [configs, search]);
+
+  const handleNewConfig = () => {
+    onStartNew();
+    onNext();
+  };
+
+  const handlePickVersion = async (config: ConfigPublic, version: number) => {
+    if (loadingVersionKey) return;
+    setLoadingVersionKey(`${config.id}:${version}`);
+    try {
+      const detail = await fetchConfigVersionDetail(
+        apiKey,
+        config.id,
+        version,
+        tag,
+      );
+      const blob = detail.config_blob as unknown as AssessmentConfigBlob;
+      onLoadExisting(blob, config.id, config.name);
+      onNext();
+    } catch (err) {
+      toast.error(
+        err instanceof Error ? err.message : "Failed to load configuration",
+      );
+    } finally {
+      // This step stays mounted (ConfigPanel hides it via CSS), so always clear
+      // the loading flag — otherwise it stays stuck on return to this step.
+      setLoadingVersionKey(null);
+    }
+  };
+
+  return (
+    <div className="flex h-full min-h-0 w-full flex-col">
+      <div className="mx-auto w-full max-w-5xl flex-1 space-y-5 pb-16">
+        <div>
+          <h2 className="text-lg font-semibold text-text-primary">
+            Configuration
+          </h2>
+          <p className="mt-1 text-sm text-text-secondary">
+            Start a new configuration, or load a saved one (and version) to edit
+            into a new version.
+          </p>
+        </div>
+
+        <div className="flex items-center gap-2">
+          <div className="relative flex-1">
+            <SearchIcon className="pointer-events-none absolute left-4 top-1/2 h-4 w-4 -translate-y-1/2 text-text-secondary" />
+            <input
+              type="text"
+              value={search}
+              onChange={(event) => setSearch(event.target.value)}
+              placeholder="Search configs..."
+              className="w-full rounded-full bg-bg-secondary py-3 pl-11 pr-4 text-sm text-text-primary placeholder:text-neutral focus:bg-bg-primary focus:outline-none focus:ring-1 focus:ring-accent-primary"
+            />
+          </div>
+          <button
+            type="button"
+            onClick={loadConfigs}
+            disabled={isLoading}
+            title="Refresh"
+            aria-label="Refresh"
+            className="cursor-pointer rounded-full p-2 text-text-secondary transition-colors hover:bg-neutral-100 hover:text-text-primary disabled:opacity-50"
+          >
+            <RefreshIcon
+              className={`h-4 w-4 ${isLoading ? "animate-spin" : ""}`}
+            />
+          </button>
+          <Button variant="primary" size="md" onClick={handleNewConfig}>
+            <PlusIcon className="h-4 w-4" />
+            New Config
+          </Button>
+        </div>
+
+        {isLoading ? (
+          <Loader size="sm" message="Loading configurations..." />
+        ) : filtered.length === 0 ? (
+          <div className="rounded-2xl border-2 border-dashed border-border bg-bg-primary p-10 text-center">
+            <p className="text-sm font-semibold text-text-primary">
+              {search.trim()
+                ? `No configs match "${search.trim()}"`
+                : "No configurations yet"}
+            </p>
+            <p className="mt-1 text-xs text-text-secondary">
+              Use “New Config” to author one from scratch.
+            </p>
+          </div>
+        ) : (
+          <div className="grid grid-cols-1 gap-4 md:grid-cols-2 xl:grid-cols-3">
+            {filtered.map((config) => (
+              <ConfigSelectCard
+                key={config.id}
+                config={config}
+                apiKey={apiKey}
+                tag={tag}
+                isLoadingId={loadingVersionKey}
+                onPick={(cfg, version) => void handlePickVersion(cfg, version)}
+              />
+            ))}
+          </div>
+        )}
+      </div>
+    </div>
+  );
+}
diff --git a/app/components/assessment/DatasetsTab.tsx b/app/components/assessment/DatasetsTab.tsx
index b45fd705..ad302120 100644
--- a/app/components/assessment/DatasetsTab.tsx
+++ b/app/components/assessment/DatasetsTab.tsx
@@ -9,13 +9,10 @@ import CreatePanel from "@/app/components/assessment/datasets/CreatePanel";
 import DatasetList from "@/app/components/assessment/datasets/DatasetList";
 
 export default function DatasetsTab(props: DatasetsTabProps) {
-  const { datasetId, onNext } = props;
   const {
     datasets,
     isLoading,
-    isLoadingColumns,
     viewingId,
-    canProceed,
     datasetName,
     datasetDescription,
     uploadedFile,
@@ -35,7 +32,6 @@ export default function DatasetsTab(props: DatasetsTabProps) {
     handleFileSelect,
     resetForm,
     handleCreateDataset,
-    handleDatasetSelect,
     handleViewDataset,
     handleDeleteDataset,
     handleDrop,
@@ -45,15 +41,10 @@ export default function DatasetsTab(props: DatasetsTabProps) {
     <div className="flex min-h-0 flex-1 overflow-hidden">
       <DatasetList
         datasets={datasets}
-        datasetId={datasetId}
         isLoading={isLoading}
-        isLoadingColumns={isLoadingColumns}
         viewingId={viewingId}
-        canProceed={canProceed}
-        onSelectDataset={handleDatasetSelect}
         onViewDataset={handleViewDataset}
         onRequestDelete={setConfirmDeleteId}
-        onNext={onNext}
       />
 
       <CreatePanel
diff --git a/app/components/assessment/EvaluationsTab.tsx b/app/components/assessment/EvaluationsTab.tsx
index d9372758..321d6ef3 100644
--- a/app/components/assessment/EvaluationsTab.tsx
+++ b/app/components/assessment/EvaluationsTab.tsx
@@ -15,6 +15,7 @@ import {
   canRetryStatus,
   formatStatusLabel,
   getResultTone,
+  isFailedStatus,
 } from "@/app/lib/assessment/results";
 import {
   ASSESSMENT_CARD_CLASSES,
@@ -59,7 +60,7 @@ export default function EvaluationsTab({ onForbidden }: EvaluationsTabProps) {
       <div className="flex-1 overflow-auto p-4">
         <div className="mb-4 flex items-center justify-between">
           <h2 className="text-base font-semibold text-text-primary">
-            Evaluation Runs
+            Assessment Runs
           </h2>
           <div className="flex items-center gap-2">
             <Select
@@ -90,7 +91,7 @@ export default function EvaluationsTab({ onForbidden }: EvaluationsTabProps) {
             <div className="p-16 text-center">
               <ClipboardIcon className="w-12 h-12 mx-auto mb-3 text-border" />
               <p className="text-sm font-medium mb-1 text-text-primary">
-                No evaluation runs yet
+                No assessment runs yet
               </p>
               <p className="text-xs text-text-secondary">
                 Submit an assessment from the Config tab to get started
@@ -127,8 +128,7 @@ export default function EvaluationsTab({ onForbidden }: EvaluationsTabProps) {
                               {formatRelativeTime(run.inserted_at)}
                             </div>
 
-                            {(run.status === "failed" ||
-                              run.status === "completed_with_errors") &&
+                            {isFailedStatus(run.status) &&
                               run.error_message && (
                                 <div className="mt-2 text-xs wrap-break-word overflow-hidden text-status-error-text">
                                   {run.error_message}
@@ -254,7 +254,7 @@ export default function EvaluationsTab({ onForbidden }: EvaluationsTabProps) {
                   No {statusFilter} runs
                 </p>
                 <p className="text-xs text-text-secondary">
-                  No evaluation runs with status &quot;{statusFilter}&quot;
+                  No assessment runs with status &quot;{statusFilter}&quot;
                 </p>
               </div>
             ))}
diff --git a/app/components/assessment/ExperimentTab.tsx b/app/components/assessment/ExperimentTab.tsx
new file mode 100644
index 00000000..9c267e16
--- /dev/null
+++ b/app/components/assessment/ExperimentTab.tsx
@@ -0,0 +1,426 @@
+"use client";
+
+// Experiment tab: pick a saved config version + a dataset, then dispatch a run.
+// Reuses the config picker from usePromptAndConfigStep and the dataset list from
+// useAssessmentDatasetsTab so no run/selection logic is re-implemented here.
+import { useState } from "react";
+import { Button, Loader, Modal, Select } from "@/app/components/ui";
+import { ExpandIcon } from "@/app/components/icons";
+import { usePromptAndConfigStep } from "@/app/hooks/usePromptAndConfigStep";
+import { useAssessmentDatasetsTab } from "@/app/hooks/useAssessmentDatasetsTab";
+import { useToast } from "@/app/hooks/useToast";
+import { useAuth } from "@/app/lib/context/AuthContext";
+import { fetchAssessmentDatasetRows } from "@/app/lib/utils/assessmentFetcher";
+import { fetchDatasetPreview } from "@/app/lib/utils/assessment";
+import type { ExperimentTabProps } from "@/app/lib/types/assessment";
+import { SavedConfigs, SelectedConfigs, UserPrompt } from "./prompt-config";
+import ExperimentReview from "./review/ExperimentReview";
+
+export default function ExperimentTab({
+  onForbidden,
+  textColumns,
+  promptTemplate,
+  setPromptTemplate,
+  configs,
+  setConfigs,
+  outputSchema,
+  systemInstruction,
+  columnMapping,
+  prefilterConfig,
+  datasetId,
+  datasetName,
+  setDatasetId,
+  setSelectedDatasetName,
+  experimentName,
+  setExperimentName,
+  isSubmitting,
+  canSubmit,
+  submitBlockerMessage,
+  onSubmit,
+}: ExperimentTabProps) {
+  const {
+    removeSelection,
+    filteredConfigCards,
+    searchQuery,
+    setSearchQuery,
+    isLoadingConfigs,
+    hasMoreConfigs,
+    nextConfigSkip,
+    expandedConfigId,
+    versionStateByConfig,
+    latestModelByConfig,
+    loadingSelectionKeys,
+    isSelected,
+    loadConfigs,
+    loadVersions,
+    toggleConfigExpansion,
+    toggleVersionSelection,
+  } = usePromptAndConfigStep({
+    textColumns,
+    promptTemplate,
+    configs,
+    setConfigs,
+    outputSchema,
+    systemInstruction,
+    columnMapping,
+    prefilterConfig,
+  });
+
+  const { datasets, isLoading, handleDatasetSelect } = useAssessmentDatasetsTab(
+    {
+      onForbidden,
+      datasetId,
+      setDatasetId,
+      setSelectedDatasetName,
+    },
+  );
+
+  const datasetOptions = datasets.map((dataset) => ({
+    value: dataset.dataset_id.toString(),
+    label: dataset.dataset_name,
+  }));
+
+  const toast = useToast();
+  const { activeKey } = useAuth();
+  const apiKey = activeKey?.key ?? "";
+  // The selected dataset's column names power the User prompt @-mention + chips.
+  const [datasetColumns, setDatasetColumns] = useState<string[]>([]);
+  const [isLoadingColumns, setIsLoadingColumns] = useState(false);
+  const [isReviewOpen, setIsReviewOpen] = useState(false);
+  const [isDownloading, setIsDownloading] = useState(false);
+  const [isPromptFullOpen, setIsPromptFullOpen] = useState(false);
+
+  // Select a dataset, then load just its headers (limit 1 row) for the prompt.
+  const handleSelectDataset = async (id: string) => {
+    handleDatasetSelect(id);
+    setDatasetColumns([]);
+    if (!id) return;
+    setIsLoadingColumns(true);
+    try {
+      const preview = await fetchDatasetPreview(id, apiKey, 1);
+      setDatasetColumns(preview.headers.filter((col) => col.trim() !== ""));
+    } catch (err) {
+      toast.error(
+        err instanceof Error ? err.message : "Failed to load dataset columns",
+      );
+    } finally {
+      setIsLoadingColumns(false);
+    }
+  };
+
+  const hasPrompt = promptTemplate.trim().length > 0;
+  const canDownload = !!datasetId && configs.length > 0 && hasPrompt;
+
+  // Build a directly-usable single-config API batch body from all dataset rows.
+  const handleDownloadInput = async () => {
+    if (!canDownload || isDownloading) return;
+    setIsDownloading(true);
+    try {
+      if (configs.length > 1) {
+        toast.warning(
+          "API batch input is single-config; used the first selected configuration.",
+        );
+      }
+      // Rows come pre-cleaned from the backend (empty columns stripped).
+      const { rows } = await fetchAssessmentDatasetRows(datasetId, apiKey);
+      const primary = configs[0];
+      const body = {
+        config: { id: primary.config_id, version: primary.config_version },
+        input: { query: promptTemplate, data: rows },
+        callback_url: "",
+        request_metadata: {},
+      };
+      const safeName = (datasetName || datasetId).replace(
+        /[^a-z0-9-_]+/gi,
+        "-",
+      );
+      const url = URL.createObjectURL(
+        new Blob([JSON.stringify(body, null, 2)], {
+          type: "application/json",
+        }),
+      );
+      const anchor = document.createElement("a");
+      anchor.href = url;
+      anchor.download = `assessment-batch-input-${safeName}.json`;
+      document.body.appendChild(anchor);
+      anchor.click();
+      anchor.remove();
+      URL.revokeObjectURL(url);
+    } catch (err) {
+      toast.error(
+        err instanceof Error ? err.message : "Failed to download API input",
+      );
+    } finally {
+      setIsDownloading(false);
+    }
+  };
+
+  if (isReviewOpen) {
+    return (
+      <div className="flex h-full min-h-0 w-full flex-col overflow-auto px-6 pt-6">
+        <div className="mx-auto w-full max-w-2xl flex-1 space-y-4 pb-8">
+          <div className="mb-2">
+            <h2 className="text-lg font-semibold text-text-primary">
+              Review &amp; Run
+            </h2>
+            <p className="mt-1 text-sm text-text-secondary">
+              Verify your experiment before running.
+            </p>
+          </div>
+
+          <ExperimentReview
+            experimentName={experimentName}
+            setExperimentName={setExperimentName}
+          />
+
+          <div className="grid gap-4 sm:grid-cols-2">
+            <div className="rounded-2xl border border-border bg-bg-primary p-4">
+              <div className="text-[11px] font-semibold uppercase tracking-wider text-text-secondary">
+                Dataset
+              </div>
+              {datasetName ? (
+                <div className="mt-2 flex items-center gap-2">
+                  <span className="h-2 w-2 shrink-0 rounded-full bg-status-success" />
+                  <span className="truncate text-sm font-medium text-text-primary">
+                    {datasetName}
+                  </span>
+                </div>
+              ) : (
+                <div className="mt-2 text-sm text-text-secondary">
+                  Not selected
+                </div>
+              )}
+            </div>
+
+            <div className="rounded-2xl border border-border bg-bg-primary p-4">
+              <div className="text-[11px] font-semibold uppercase tracking-wider text-text-secondary">
+                Configuration{configs.length > 1 ? "s" : ""}
+                {configs.length > 0 && (
+                  <span className="ml-1 font-normal normal-case">
+                    ({configs.length})
+                  </span>
+                )}
+              </div>
+              {configs.length > 0 ? (
+                <ul className="mt-2 space-y-2">
+                  {configs.map((config) => (
+                    <li
+                      key={`${config.config_id}-${config.config_version}`}
+                      className="min-w-0"
+                    >
+                      <div className="flex items-center gap-2">
+                        <span className="truncate text-sm font-medium text-text-primary">
+                          {config.name ?? "Configuration"}
+                        </span>
+                        <span className="inline-flex shrink-0 items-center rounded-full bg-bg-secondary px-2 py-0.5 font-mono text-[10px] font-semibold text-text-secondary">
+                          v{config.config_version}
+                        </span>
+                      </div>
+                      <div className="truncate font-mono text-[11px] text-text-secondary">
+                        {config.config_id}
+                      </div>
+                    </li>
+                  ))}
+                </ul>
+              ) : (
+                <div className="mt-2 text-sm text-text-secondary">
+                  None selected
+                </div>
+              )}
+            </div>
+          </div>
+
+          <div className="overflow-hidden rounded-2xl border border-border bg-bg-primary">
+            <div className="flex items-center justify-between border-b border-border bg-bg-secondary px-4 py-2.5">
+              <span className="text-[11px] font-semibold uppercase tracking-wider text-text-secondary">
+                User prompt
+              </span>
+              {hasPrompt && (
+                <button
+                  type="button"
+                  onClick={() => setIsPromptFullOpen(true)}
+                  aria-label="Expand user prompt"
+                  title="Expand"
+                  className="cursor-pointer rounded-md p-1 text-text-secondary transition-colors hover:bg-bg-primary hover:text-text-primary"
+                >
+                  <ExpandIcon className="h-4 w-4" />
+                </button>
+              )}
+            </div>
+            {hasPrompt ? (
+              <pre className="h-40 overflow-auto whitespace-pre-wrap break-words px-4 py-3 font-mono text-xs leading-6 text-text-primary">
+                {promptTemplate}
+              </pre>
+            ) : (
+              <div className="px-4 py-3 text-sm text-text-secondary">
+                Not set
+              </div>
+            )}
+          </div>
+
+          <Modal
+            open={isPromptFullOpen}
+            onClose={() => setIsPromptFullOpen(false)}
+            title="User prompt"
+            maxWidth="max-w-3xl"
+            maxHeight="max-h-[90vh]"
+          >
+            <pre className="max-h-[70vh] overflow-auto whitespace-pre-wrap break-words px-6 pb-6 font-mono text-sm leading-7 text-text-primary">
+              {promptTemplate}
+            </pre>
+          </Modal>
+        </div>
+
+        <div className="sticky bottom-0 z-10 mt-auto -mx-6 flex flex-wrap items-center justify-between gap-3 border-t border-border bg-bg-secondary px-6 py-3">
+          <Button
+            type="button"
+            variant="outline"
+            size="lg"
+            onClick={() => setIsReviewOpen(false)}
+            className="!rounded-lg !px-6"
+          >
+            Back
+          </Button>
+          <div className="flex flex-wrap items-center gap-3">
+            {!canSubmit && submitBlockerMessage && (
+              <span className="text-xs text-text-secondary">
+                {submitBlockerMessage}
+              </span>
+            )}
+            <Button
+              type="button"
+              variant="outline"
+              size="lg"
+              onClick={() => void handleDownloadInput()}
+              disabled={!canDownload || isDownloading}
+              className="!rounded-lg !px-6"
+            >
+              {isDownloading ? "Preparing..." : "Download batch API input JSON"}
+            </Button>
+            <Button
+              type="button"
+              size="lg"
+              onClick={onSubmit}
+              disabled={!canSubmit || isSubmitting}
+              className="!rounded-lg !px-6"
+            >
+              {isSubmitting ? "Running..." : "Run experiment"}
+            </Button>
+          </div>
+        </div>
+      </div>
+    );
+  }
+
+  return (
+    <div className="flex h-full min-h-0 w-full flex-col overflow-auto px-6 pt-6">
+      <div className="mx-auto w-full max-w-7xl flex-1 pb-24">
+        <div className="mb-6">
+          <h2 className="text-xl font-semibold text-text-primary">
+            Experiment
+          </h2>
+          <p className="mt-1 text-sm text-text-secondary">
+            Pick a saved configuration and a dataset, then run the assessment.
+          </p>
+        </div>
+
+        <div className="grid gap-8 lg:grid-cols-[minmax(0,1.02fr)_minmax(330px,1fr)] xl:grid-cols-[minmax(0,1fr)_minmax(360px,1.05fr)]">
+          <section className="min-w-0 space-y-6">
+            <div className="rounded-2xl border border-border bg-bg-primary p-4">
+              <div className="mb-2 text-sm font-semibold text-text-primary">
+                Dataset
+              </div>
+              {isLoading ? (
+                <Loader size="sm" message="Loading datasets..." />
+              ) : (
+                <Select
+                  value={datasetId}
+                  placeholder="Select a dataset"
+                  options={datasetOptions}
+                  onChange={(event) =>
+                    void handleSelectDataset(event.target.value)
+                  }
+                />
+              )}
+              {datasetName && (
+                <p className="mt-2 text-xs text-text-secondary">
+                  Selected: {datasetName}
+                  {isLoadingColumns
+                    ? " · loading columns…"
+                    : datasetColumns.length > 0
+                      ? ` · ${datasetColumns.length} columns`
+                      : ""}
+                </p>
+              )}
+            </div>
+
+            <div className="rounded-2xl border border-border bg-bg-primary p-4">
+              <div className="mb-2 text-sm font-semibold text-text-primary">
+                User prompt
+              </div>
+              <UserPrompt
+                textColumns={datasetColumns}
+                promptTemplate={promptTemplate}
+                setPromptTemplate={setPromptTemplate}
+                previewMode={false}
+              />
+            </div>
+          </section>
+
+          <aside className="self-start space-y-5 lg:sticky lg:top-6 lg:min-w-[330px] xl:min-w-[360px]">
+            <div className="rounded-2xl border border-border bg-bg-primary p-4">
+              <div className="mb-3 text-sm font-semibold text-text-primary">
+                Configuration
+                <span className="ml-2 text-xs font-normal text-text-secondary">
+                  {configs.length > 0
+                    ? `${configs.length} selected`
+                    : "Choose at least one saved configuration"}
+                </span>
+              </div>
+
+              {configs.length > 0 && (
+                <div className="mb-4">
+                  <SelectedConfigs
+                    configs={configs}
+                    onRemove={removeSelection}
+                  />
+                </div>
+              )}
+
+              <SavedConfigs
+                configCards={filteredConfigCards}
+                searchQuery={searchQuery}
+                setSearchQuery={setSearchQuery}
+                isLoadingConfigs={isLoadingConfigs}
+                hasMoreConfigs={hasMoreConfigs}
+                nextConfigSkip={nextConfigSkip}
+                expandedConfigId={expandedConfigId}
+                versionStateByConfig={versionStateByConfig}
+                latestModelByConfig={latestModelByConfig}
+                loadingSelectionKeys={loadingSelectionKeys}
+                isSelected={isSelected}
+                onLoadMoreConfigs={(skip) => loadConfigs(skip, false)}
+                onLoadVersions={(configId, skip) =>
+                  void loadVersions(configId, skip)
+                }
+                onToggleConfigExpansion={toggleConfigExpansion}
+                onToggleVersionSelection={toggleVersionSelection}
+              />
+            </div>
+          </aside>
+        </div>
+      </div>
+
+      <div className="sticky bottom-0 z-10 mt-auto -mx-6 flex items-center justify-end gap-3 border-t border-border bg-bg-secondary px-6 py-3">
+        <Button
+          type="button"
+          size="lg"
+          onClick={() => setIsReviewOpen(true)}
+          className="!rounded-lg !px-6"
+        >
+          Review
+        </Button>
+      </div>
+    </div>
+  );
+}
diff --git a/app/components/assessment/PageLayout.tsx b/app/components/assessment/PageLayout.tsx
index 84dd490e..472e063f 100644
--- a/app/components/assessment/PageLayout.tsx
+++ b/app/components/assessment/PageLayout.tsx
@@ -1,29 +1,34 @@
 "use client";
 
-// Top-level layout for /assessment: sidebar, tab navigation, and active tab content.
+// Top-level layout for /assessment. Tabs are sidebar sub-items (routes), so the
+// active tab is driven by the URL rather than an in-page tab bar.
+import { usePathname } from "next/navigation";
 import Sidebar from "@/app/components/Sidebar";
-import { TabNavigation } from "@/app/components/ui";
 import PageHeader from "@/app/components/PageHeader";
 import { useApp } from "@/app/lib/context/AppContext";
 import type { PageLayoutProps } from "@/app/lib/types/assessment";
 import ConfigPanel from "./ConfigPanel";
 import DatasetsTab from "./DatasetsTab";
 import EvaluationsTab from "./EvaluationsTab";
+import ExperimentTab from "./ExperimentTab";
 
 export default function PageLayout({
   activeTab,
-  tabs,
-  onTabSwitch,
   datasetsTabProps,
   configPanelProps,
+  experimentTabProps,
   evaluationsTabProps,
 }: PageLayoutProps) {
   const { sidebarCollapsed } = useApp();
+  const pathname = usePathname();
 
   return (
     <div className="flex h-screen w-full flex-col bg-neutral-50">
       <div className="flex flex-1 overflow-hidden">
-        <Sidebar collapsed={sidebarCollapsed} activeRoute="/assessment" />
+        <Sidebar
+          collapsed={sidebarCollapsed}
+          activeRoute={pathname ?? undefined}
+        />
 
         <div className="flex-1 flex flex-col overflow-hidden">
           <PageHeader
@@ -31,12 +36,6 @@ export default function PageLayout({
             subtitle="Multi-modal batch evaluation with prompt templates, attachments, and config comparison"
           />
 
-          <TabNavigation
-            activeTab={activeTab}
-            tabs={tabs}
-            onTabChange={(tabId) => onTabSwitch(tabId as typeof activeTab)}
-          />
-
           {activeTab === "datasets" && (
             <div className="flex-1 overflow-hidden flex flex-col">
               <DatasetsTab {...datasetsTabProps} />
@@ -51,6 +50,12 @@ export default function PageLayout({
             <ConfigPanel {...configPanelProps} />
           </div>
 
+          {activeTab === "experiment" && (
+            <div className="flex-1 overflow-hidden flex flex-col">
+              <ExperimentTab {...experimentTabProps} />
+            </div>
+          )}
+
           {activeTab === "results" && (
             <div className="flex-1 overflow-hidden flex flex-col">
               <EvaluationsTab {...evaluationsTabProps} />
diff --git a/app/components/assessment/PrefilterStep.tsx b/app/components/assessment/PrefilterStep.tsx
index 0ad16cd5..b2c65895 100644
--- a/app/components/assessment/PrefilterStep.tsx
+++ b/app/components/assessment/PrefilterStep.tsx
@@ -1,6 +1,6 @@
 "use client";
 
-import { useState } from "react";
+import { useEffect, useRef, useState } from "react";
 import { Button, Modal } from "@/app/components/ui";
 import { ExpandIcon } from "@/app/components/icons";
 import CompactToggleSwitch from "@/app/components/assessment/CompactToggleSwitch";
@@ -60,6 +60,7 @@ export default function PrefilterStep({
   setPrefilterConfig,
   onNext,
   onBack,
+  syncToken,
 }: PrefilterStepProps) {
   const [trEnabled, setTrEnabled] = useState(
     () => !!prefilterConfig?.topic_relevance,
@@ -84,6 +85,30 @@ export default function PrefilterStep({
   );
   const [isPromptModalOpen, setIsPromptModalOpen] = useState(false);
 
+  // Re-seed local state from props whenever a config is (re)loaded. Keyed on
+  // syncToken only so ongoing edits (which flow to prefilterConfig on Next) are
+  // not clobbered mid-edit.
+  const propsRef = useRef({ prefilterConfig, attachmentColumns });
+  useEffect(() => {
+    propsRef.current = { prefilterConfig, attachmentColumns };
+  });
+  const isFirstSyncRef = useRef(true);
+  useEffect(() => {
+    if (isFirstSyncRef.current) {
+      isFirstSyncRef.current = false;
+      return;
+    }
+    const { prefilterConfig: pf, attachmentColumns: attach } = propsRef.current;
+    setTrEnabled(!!pf?.topic_relevance);
+    setDupEnabled(!!pf?.duplicate_detection);
+    setTrColumns(pf?.topic_relevance?.columns ?? []);
+    setTrAttachmentColumns(pf?.topic_relevance?.attachment_columns ?? attach);
+    setTrPrompt(
+      pf?.topic_relevance?.prompt ?? DEFAULT_PREFILTER_TOPIC_RELEVANCE_PROMPT,
+    );
+    setDupColumns(pf?.duplicate_detection?.columns ?? []);
+  }, [syncToken]);
+
   const trHasColumns = trColumns.length > 0 || trAttachmentColumns.length > 0;
 
   const handleNext = () => {
@@ -113,11 +138,11 @@ export default function PrefilterStep({
       <div className="mx-auto w-full max-w-3xl flex-1 space-y-6 pb-16">
         <div>
           <h2 className="text-lg font-semibold text-text-primary">
-            Eliminatory
+            Pre-filter
           </h2>
           <p className="mt-1 text-sm text-text-secondary">
             Optional pre-filters run before the LLM batch. Rows that fail Topic
-            Relevance are excluded from Evaluation and flagged in the export.
+            Relevance are excluded from Assessment and flagged in the export.
           </p>
         </div>
 
@@ -128,7 +153,7 @@ export default function PrefilterStep({
                 Topic Relevance
               </div>
               <div className="mt-0.5 text-xs text-text-secondary">
-                Gate: rows with decision=REJECT are excluded from Evaluation.
+                Gate: rows with decision=REJECT are excluded from Assessment.
               </div>
             </div>
             <CompactToggleSwitch
@@ -196,7 +221,7 @@ export default function PrefilterStep({
               <div>
                 <div className="mb-1.5 flex items-center justify-between">
                   <span className="block text-xs font-medium text-text-secondary">
-                    Evaluation prompt / rubric
+                    Assessment prompt / rubric
                     <span className="ml-1 text-status-error-text">*</span>
                   </span>
                   <button
@@ -218,7 +243,7 @@ export default function PrefilterStep({
                 />
                 {!trPrompt.trim() && (
                   <p className="mt-1 text-xs text-status-warning">
-                    Evaluation prompt is required.
+                    Assessment prompt is required.
                   </p>
                 )}
               </div>
@@ -234,7 +259,7 @@ export default function PrefilterStep({
               </div>
               <div className="mt-0.5 text-xs text-text-secondary">
                 Passthrough: runs only on rows that passed Topic Relevance.
-                Results appear in export; does not gate Evaluation.
+                Results appear in export; does not gate Assessment.
               </div>
             </div>
             <CompactToggleSwitch
@@ -267,7 +292,7 @@ export default function PrefilterStep({
       <Modal
         open={isPromptModalOpen}
         onClose={() => setIsPromptModalOpen(false)}
-        title="Evaluation prompt / rubric"
+        title="Assessment prompt / rubric"
         maxWidth="max-w-4xl"
         maxHeight="max-h-[85vh]"
       >
@@ -295,13 +320,13 @@ export default function PrefilterStep({
           <div className="flex flex-col gap-3 sm:flex-row sm:items-center">
             <span className="text-xs text-text-secondary">
               {!trEnabled && !dupEnabled
-                ? "No filters enabled — Eliminatory will be skipped."
+                ? "No filters enabled — Pre-filter will be skipped."
                 : canProceed
                   ? "Ready to continue."
                   : "Complete required fields above."}
             </span>
             <Button type="button" onClick={handleNext} disabled={!canProceed}>
-              Next: Evaluation
+              Next: Assessment
             </Button>
           </div>
         </div>
diff --git a/app/components/assessment/PromptAndConfigStep.tsx b/app/components/assessment/PromptAndConfigStep.tsx
index 6e1eafb1..72f6e386 100644
--- a/app/components/assessment/PromptAndConfigStep.tsx
+++ b/app/components/assessment/PromptAndConfigStep.tsx
@@ -1,8 +1,10 @@
 "use client";
 
-import { Button } from "@/app/components/ui";
-import { ChevronLeftIcon } from "@/app/components/icons";
+import { useState } from "react";
+import { Button, Modal } from "@/app/components/ui";
+import { ChevronLeftIcon, ExpandIcon } from "@/app/components/icons";
 import { usePromptAndConfigStep } from "@/app/hooks/usePromptAndConfigStep";
+import { ASSESSMENT_TAG } from "@/app/lib/assessment/constants";
 import type { PromptAndConfigStepProps } from "@/app/lib/types/assessment";
 import {
   AssessmentConfiguration,
@@ -13,16 +15,11 @@ import {
 
 export default function PromptAndConfigStep(props: PromptAndConfigStepProps) {
   const {
-    textColumns,
-    sampleRow,
     systemInstruction,
     setSystemInstruction,
-    promptTemplate,
-    setPromptTemplate,
     configs,
     outputSchema,
     setOutputSchema,
-    onNext,
     onBack,
   } = props;
 
@@ -30,26 +27,6 @@ export default function PromptAndConfigStep(props: PromptAndConfigStepProps) {
     promptStatus,
     responseSummary,
     hasConfiguredResponseFormat,
-    canProceed,
-    nextBlockerMessage,
-    configMode,
-    setConfigMode,
-    removeSelection,
-    filteredConfigCards,
-    searchQuery,
-    setSearchQuery,
-    isLoadingConfigs,
-    hasMoreConfigs,
-    nextConfigSkip,
-    expandedConfigId,
-    versionStateByConfig,
-    latestModelByConfig,
-    loadingSelectionKeys,
-    isSelected,
-    loadConfigs,
-    loadVersions,
-    toggleConfigExpansion,
-    toggleVersionSelection,
     currentProvider,
     currentModel,
     providerModels,
@@ -58,24 +35,70 @@ export default function PromptAndConfigStep(props: PromptAndConfigStepProps) {
     configName,
     commitMessage,
     isSaving,
+    saveMode,
+    setSaveMode,
+    versionConfigId,
+    setVersionConfigId,
+    filteredConfigCards,
     setConfigName,
     setCommitMessage,
     handleProviderChange,
     handleModelChange,
     updateDraftParam,
     handleCreateAndAdd,
+    configBlob,
   } = usePromptAndConfigStep(props);
 
+  const [isSaveModalOpen, setIsSaveModalOpen] = useState(false);
+  const [isPromptFullOpen, setIsPromptFullOpen] = useState(false);
+
+  const handleDownloadConfig = () => {
+    // Shape matches the API body the save will use:
+    // - new config  -> POST /configs        : { name, tag, commit_message, config_blob }
+    // - new version -> POST /configs/{id}/versions : { config_blob, commit_message }
+    // name/commit are left as skeleton placeholders for the user to fill.
+    const payload =
+      saveMode === "version"
+        ? {
+            config_blob: configBlob,
+            commit_message: commitMessage.trim(),
+          }
+        : {
+            name: configName.trim(),
+            tag: ASSESSMENT_TAG,
+            commit_message: commitMessage.trim(),
+            config_blob: configBlob,
+          };
+    const baseName =
+      saveMode === "version"
+        ? configName.trim() || versionConfigId || "assessment-config-version"
+        : configName.trim() || "assessment-config";
+    const fileName = baseName.replace(/[^a-z0-9-_]+/gi, "-");
+    const url = URL.createObjectURL(
+      new Blob([JSON.stringify(payload, null, 2)], {
+        type: "application/json",
+      }),
+    );
+    const anchor = document.createElement("a");
+    anchor.href = url;
+    anchor.download = `${fileName}.json`;
+    document.body.appendChild(anchor);
+    anchor.click();
+    anchor.remove();
+    URL.revokeObjectURL(url);
+  };
+
   return (
     <div className="flex h-full min-h-0 w-full flex-col">
       <div className="mx-auto w-full max-w-7xl flex-1 pb-20">
         <div className="mb-6 flex flex-col gap-4 lg:flex-row lg:items-start lg:justify-between">
           <div>
             <h2 className="text-xl font-semibold text-text-primary">
-              Evaluation
+              Assessment
             </h2>
             <p className="mt-1 text-sm text-text-secondary">
-              Write the task on the left. Tune behavior and output on the right.
+              Edit the system prompt, response format, and model on the left —
+              scroll to reach each. Live preview on the right.
             </p>
           </div>
           <SetupProgress
@@ -85,17 +108,13 @@ export default function PromptAndConfigStep(props: PromptAndConfigStepProps) {
           />
         </div>
 
-        <div className="grid gap-8 lg:grid-cols-[minmax(0,1.02fr)_minmax(330px,1fr)] xl:grid-cols-[minmax(0,1fr)_minmax(360px,1.05fr)]">
-          <PromptPanel
-            textColumns={textColumns}
-            sampleRow={sampleRow}
-            systemInstruction={systemInstruction}
-            setSystemInstruction={setSystemInstruction}
-            promptTemplate={promptTemplate}
-            setPromptTemplate={setPromptTemplate}
-          />
+        <div className="grid gap-8 lg:grid-cols-2">
+          <section className="min-w-0 space-y-5">
+            <PromptPanel
+              systemInstruction={systemInstruction}
+              setSystemInstruction={setSystemInstruction}
+            />
 
-          <aside className="self-start space-y-5 lg:sticky lg:top-6 lg:min-w-[330px] xl:min-w-[360px]">
             <ResponseSchema
               schema={outputSchema}
               setSchema={setOutputSchema}
@@ -104,27 +123,6 @@ export default function PromptAndConfigStep(props: PromptAndConfigStepProps) {
             />
 
             <AssessmentConfiguration
-              configMode={configMode}
-              setConfigMode={setConfigMode}
-              configs={configs}
-              onRemoveConfig={removeSelection}
-              configCards={filteredConfigCards}
-              searchQuery={searchQuery}
-              setSearchQuery={setSearchQuery}
-              isLoadingConfigs={isLoadingConfigs}
-              hasMoreConfigs={hasMoreConfigs}
-              nextConfigSkip={nextConfigSkip}
-              expandedConfigId={expandedConfigId}
-              versionStateByConfig={versionStateByConfig}
-              latestModelByConfig={latestModelByConfig}
-              loadingSelectionKeys={loadingSelectionKeys}
-              isSelected={isSelected}
-              onLoadMoreConfigs={(skip) => loadConfigs(skip, false)}
-              onLoadVersions={(configId, skip) =>
-                void loadVersions(configId, skip)
-              }
-              onToggleConfigExpansion={toggleConfigExpansion}
-              onToggleVersionSelection={toggleVersionSelection}
               currentProvider={currentProvider}
               currentModel={currentModel}
               providerModels={providerModels}
@@ -133,6 +131,13 @@ export default function PromptAndConfigStep(props: PromptAndConfigStepProps) {
               configName={configName}
               commitMessage={commitMessage}
               isSaving={isSaving}
+              isSaveModalOpen={isSaveModalOpen}
+              setIsSaveModalOpen={setIsSaveModalOpen}
+              saveMode={saveMode}
+              setSaveMode={setSaveMode}
+              versionConfigId={versionConfigId}
+              setVersionConfigId={setVersionConfigId}
+              existingConfigs={filteredConfigCards}
               setConfigName={setConfigName}
               setCommitMessage={setCommitMessage}
               onProviderChange={handleProviderChange}
@@ -140,11 +145,98 @@ export default function PromptAndConfigStep(props: PromptAndConfigStepProps) {
               onParamChange={updateDraftParam}
               onSaveConfig={handleCreateAndAdd}
             />
+          </section>
+
+          <aside className="self-start lg:sticky lg:top-6 lg:border-l lg:border-border lg:pl-8">
+            <div className="overflow-hidden rounded-2xl border border-border bg-bg-primary shadow-sm">
+              <div className="border-b border-border bg-bg-secondary px-5 py-3 text-xs font-semibold uppercase tracking-wider text-text-secondary">
+                Preview
+              </div>
+              <div className="space-y-6 p-5 text-sm">
+                <div>
+                  <div className="mb-2 text-[11px] font-semibold uppercase tracking-wider text-text-secondary">
+                    Model
+                  </div>
+                  <div className="flex flex-wrap items-center gap-2">
+                    <span className="inline-flex items-center rounded-full bg-bg-secondary px-2.5 py-1 text-xs font-medium text-text-primary">
+                      {currentProvider}
+                    </span>
+                    <span className="rounded-md bg-bg-secondary px-2 py-1 font-mono text-xs text-text-primary">
+                      {currentModel}
+                    </span>
+                  </div>
+                </div>
+
+                <div>
+                  <div className="mb-2 flex items-center justify-between">
+                    <span className="text-[11px] font-semibold uppercase tracking-wider text-text-secondary">
+                      System prompt
+                    </span>
+                    {systemInstruction.trim() && (
+                      <button
+                        type="button"
+                        onClick={() => setIsPromptFullOpen(true)}
+                        aria-label="Expand system prompt"
+                        title="Expand"
+                        className="cursor-pointer rounded-md p-1 text-text-secondary transition-colors hover:bg-bg-secondary hover:text-text-primary"
+                      >
+                        <ExpandIcon className="h-4 w-4" />
+                      </button>
+                    )}
+                  </div>
+                  {systemInstruction.trim() ? (
+                    <div className="max-h-[420px] overflow-y-auto whitespace-pre-wrap break-words rounded-xl border border-border bg-bg-secondary px-4 py-3 font-mono text-xs leading-6 text-text-primary">
+                      {systemInstruction}
+                    </div>
+                  ) : (
+                    <div className="rounded-xl border border-dashed border-border px-4 py-6 text-center text-xs text-text-secondary">
+                      No system prompt yet
+                    </div>
+                  )}
+                </div>
+
+                <div>
+                  <div className="mb-2 text-[11px] font-semibold uppercase tracking-wider text-text-secondary">
+                    Response format
+                  </div>
+                  {hasConfiguredResponseFormat ? (
+                    <ul className="flex flex-wrap gap-2">
+                      {outputSchema
+                        .filter((field) => field.name.trim())
+                        .map((field) => (
+                          <li
+                            key={field.id}
+                            className="inline-flex items-center rounded-full border border-border bg-bg-secondary px-2.5 py-1 font-mono text-[11px] text-text-primary"
+                          >
+                            {field.name}
+                          </li>
+                        ))}
+                    </ul>
+                  ) : (
+                    <div className="text-xs text-text-secondary">
+                      Free text (no structured output)
+                    </div>
+                  )}
+                </div>
+              </div>
+            </div>
           </aside>
         </div>
       </div>
 
-      <div className="sticky bottom-0 z-10 mt-auto -mx-6 flex items-center justify-between border-t border-border bg-bg-secondary px-6 py-2">
+      <Modal
+        open={isPromptFullOpen}
+        onClose={() => setIsPromptFullOpen(false)}
+        title="System prompt"
+        maxWidth="max-w-3xl"
+        maxHeight="max-h-[90vh]"
+      >
+        <pre className="max-h-[70vh] overflow-auto whitespace-pre-wrap break-words px-6 pb-6 font-mono text-sm leading-7 text-text-primary">
+          {systemInstruction}
+        </pre>
+      </Modal>
+
+      <div className="sticky bottom-0 z-10 mt-auto -mx-6 border-t border-border bg-bg-secondary px-6 py-2">
         <div className="mx-auto flex w-full max-w-5xl items-center justify-between">
           <Button
             type="button"
@@ -157,18 +249,23 @@ export default function PromptAndConfigStep(props: PromptAndConfigStepProps) {
             Back
           </Button>
           <div className="flex items-center gap-3">
-            {!canProceed && (
-              <span className="text-xs text-text-secondary">
-                {nextBlockerMessage}
-              </span>
-            )}
+            <Button
+              type="button"
+              variant="outline"
+              size="lg"
+              onClick={handleDownloadConfig}
+              className="!rounded-lg !px-6"
+            >
+              Download config JSON
+            </Button>
             <Button
               type="button"
               size="lg"
-              onClick={onNext}
-              disabled={!canProceed}
+              onClick={() => setIsSaveModalOpen(true)}
+              disabled={isSaving}
+              className="!rounded-lg !px-6"
             >
-              Next: Review
+              {isSaving ? "Saving..." : "Save behavior"}
             </Button>
           </div>
         </div>
diff --git a/app/components/assessment/ReviewStep.tsx b/app/components/assessment/ReviewStep.tsx
index 3f68cdd8..a9246f23 100644
--- a/app/components/assessment/ReviewStep.tsx
+++ b/app/components/assessment/ReviewStep.tsx
@@ -83,7 +83,7 @@ export default function ReviewStep({
             Review & Submit
           </h2>
           <p className="mt-1 text-sm text-text-secondary">
-            Verify your evaluation configuration before submitting.
+            Verify your assessment configuration before submitting.
           </p>
         </div>
 
diff --git a/app/components/assessment/datasets/CreatePanel.tsx b/app/components/assessment/datasets/CreatePanel.tsx
index ce0dd22f..51b29d8c 100644
--- a/app/components/assessment/datasets/CreatePanel.tsx
+++ b/app/components/assessment/datasets/CreatePanel.tsx
@@ -51,7 +51,7 @@ export default function CreatePanel({
             Create New Dataset
           </h2>
           <p className="mt-0.5 text-xs text-text-secondary">
-            Upload a CSV file for evaluation
+            Upload a CSV file for assessment
           </p>
         </div>
 
diff --git a/app/components/assessment/datasets/DatasetList.tsx b/app/components/assessment/datasets/DatasetList.tsx
index cbaf5a5a..f7385cc9 100644
--- a/app/components/assessment/datasets/DatasetList.tsx
+++ b/app/components/assessment/datasets/DatasetList.tsx
@@ -9,47 +9,30 @@ import { Button } from "@/app/components/ui";
 
 interface DatasetListProps {
   datasets: Dataset[];
-  datasetId: string;
   isLoading: boolean;
-  isLoadingColumns: boolean;
   viewingId: number | null;
-  canProceed: boolean;
-  onSelectDataset: (id: string, name?: string) => void;
   onViewDataset: (datasetId: number, name: string) => void;
   onRequestDelete: ValueSetter<number>;
-  onNext: () => void;
 }
 
 export default function DatasetList({
   datasets,
-  datasetId,
   isLoading,
-  isLoadingColumns,
   viewingId,
-  canProceed,
-  onSelectDataset,
   onViewDataset,
   onRequestDelete,
-  onNext,
 }: DatasetListProps) {
   return (
     <div className="flex min-h-0 flex-1 flex-col overflow-hidden bg-bg-secondary">
       <div className="flex-1 overflow-auto p-6">
-        <div className="mb-4 flex items-center justify-between">
-          <div>
-            <h3 className="text-base font-semibold text-text-primary">
-              Datasets
-            </h3>
-            <p className="mt-2 rounded-full border border-accent-secondary bg-accent-secondary/15 px-3 py-2 text-xs font-medium text-text-primary">
-              Use an existing dataset from the list, or create a new dataset
-              from the form on the right.
-            </p>
-          </div>
-          {isLoadingColumns && (
-            <span className="text-xs text-text-secondary">
-              Loading columns...
-            </span>
-          )}
+        <div className="mb-4">
+          <h3 className="text-base font-semibold text-text-primary">
+            Datasets
+          </h3>
+          <p className="mt-2 rounded-full border border-accent-secondary bg-accent-secondary/15 px-3 py-2 text-xs font-medium text-text-primary">
+            Manage your dataset library. Create a dataset from the form on the
+            right; pick one to run when you set up an experiment.
+          </p>
         </div>
 
         {isLoading ? (
@@ -66,102 +49,72 @@ export default function DatasetList({
           </div>
         ) : (
           <div className="space-y-3">
-            {datasets.map((dataset) => {
-              const isSelected = datasetId === dataset.dataset_id.toString();
-              return (
-                <div
-                  key={dataset.dataset_id}
-                  className={`cursor-pointer overflow-hidden rounded-lg border-l-[3px] bg-bg-primary transition-all ${
-                    isSelected
-                      ? "border-l-accent-primary ring-1 ring-accent-primary shadow-sm"
-                      : "border-l-accent-secondary shadow-[0_1px_3px_rgba(0,0,0,0.04)]"
-                  }`}
-                  onClick={() =>
-                    onSelectDataset(
-                      dataset.dataset_id.toString(),
-                      dataset.dataset_name,
-                    )
-                  }
-                >
-                  <div className="px-5 py-4">
-                    <div className="flex items-start justify-between gap-4">
-                      <div className="min-w-0 flex-1">
-                        <div className="flex items-center gap-2">
-                          <div className="truncate text-sm font-semibold text-text-primary">
-                            {dataset.dataset_name}
-                          </div>
-                        </div>
-                        {dataset.description && (
-                          <EvalDatasetDescription
-                            description={dataset.description}
-                          />
-                        )}
-                        <div className="mt-2 flex items-center gap-3 text-xs text-text-secondary">
-                          <span>{dataset.total_items} items</span>
-                          {dataset.original_items > 0 &&
-                            dataset.original_items !== dataset.total_items && (
-                              <>
-                                <span className="text-border">·</span>
-                                <span>{dataset.original_items} original</span>
-                              </>
-                            )}
+            {datasets.map((dataset) => (
+              <div
+                key={dataset.dataset_id}
+                className="overflow-hidden rounded-lg border-l-[3px] border-l-accent-secondary bg-bg-primary shadow-[0_1px_3px_rgba(0,0,0,0.04)]"
+              >
+                <div className="px-5 py-4">
+                  <div className="flex items-start justify-between gap-4">
+                    <div className="min-w-0 flex-1">
+                      <div className="flex items-center gap-2">
+                        <div className="truncate text-sm font-semibold text-text-primary">
+                          {dataset.dataset_name}
                         </div>
                       </div>
-                      <div className="flex flex-shrink-0 items-center gap-2">
-                        <Button
-                          type="button"
-                          variant="outline"
-                          size="sm"
-                          onClick={(event) => {
-                            event.stopPropagation();
-                            onViewDataset(
-                              dataset.dataset_id,
-                              dataset.dataset_name,
-                            );
-                          }}
-                          disabled={viewingId === dataset.dataset_id}
-                          className={` ${
-                            viewingId === dataset.dataset_id ? "opacity-50" : ""
-                          }`}
-                        >
-                          {viewingId === dataset.dataset_id
-                            ? "Loading..."
-                            : "View"}
-                        </Button>
-                        <Button
-                          type="button"
-                          variant="outline"
-                          size="sm"
-                          onClick={(event) => {
-                            event.stopPropagation();
-                            onRequestDelete(dataset.dataset_id);
-                          }}
-                          aria-label={`Delete ${dataset.dataset_name}`}
-                        >
-                          Delete
-                        </Button>
+                      {dataset.description && (
+                        <EvalDatasetDescription
+                          description={dataset.description}
+                        />
+                      )}
+                      <div className="mt-2 flex items-center gap-3 text-xs text-text-secondary">
+                        <span>{dataset.total_items} items</span>
+                        {dataset.original_items > 0 &&
+                          dataset.original_items !== dataset.total_items && (
+                            <>
+                              <span className="text-border">·</span>
+                              <span>{dataset.original_items} original</span>
+                            </>
+                          )}
                       </div>
                     </div>
+                    <div className="flex flex-shrink-0 items-center gap-2">
+                      <Button
+                        type="button"
+                        variant="outline"
+                        size="sm"
+                        onClick={() =>
+                          onViewDataset(
+                            dataset.dataset_id,
+                            dataset.dataset_name,
+                          )
+                        }
+                        disabled={viewingId === dataset.dataset_id}
+                        className={` ${
+                          viewingId === dataset.dataset_id ? "opacity-50" : ""
+                        }`}
+                      >
+                        {viewingId === dataset.dataset_id
+                          ? "Loading..."
+                          : "View"}
+                      </Button>
+                      <Button
+                        type="button"
+                        variant="outline"
+                        size="sm"
+                        onClick={() => onRequestDelete(dataset.dataset_id)}
+                        aria-label={`Delete ${dataset.dataset_name}`}
+                      >
+                        Delete
+                      </Button>
+                    </div>
                   </div>
                 </div>
-              );
-            })}
+              </div>
+            ))}
           </div>
         )}
       </div>
-
-      <div className="sticky bottom-0 z-10 flex shrink-0 items-center justify-between border-t border-border bg-bg-primary px-6 py-3">
-        <div className="mx-auto flex w-full max-w-5xl items-center justify-between">
-          <span className="text-xs text-text-secondary">
-            {canProceed
-              ? "Dataset selected. Continue to AI configuration."
-              : "Select a dataset to continue."}
-          </span>
-          <Button type="button" onClick={onNext} disabled={!canProceed}>
-            Next: AI Configuration
-          </Button>
-        </div>
-      </div>
     </div>
   );
 }
diff --git a/app/components/assessment/prompt-config/AssessmentConfiguration.tsx b/app/components/assessment/prompt-config/AssessmentConfiguration.tsx
index a0465778..49b23a25 100644
--- a/app/components/assessment/prompt-config/AssessmentConfiguration.tsx
+++ b/app/components/assessment/prompt-config/AssessmentConfiguration.tsx
@@ -1,32 +1,9 @@
 "use client";
 
-import { RadioGroup } from "@/app/components/ui";
 import type { AssessmentConfigurationProps } from "@/app/lib/types/assessment";
-import type { ConfigMode } from "@/app/lib/types/assessment/config";
 import ConfigCreator from "./ConfigCreator";
-import SavedConfigs from "./SavedConfigs";
-import SelectedConfigs from "./SelectedConfigs";
 
 export default function AssessmentConfiguration({
-  configMode,
-  setConfigMode,
-  configs,
-  onRemoveConfig,
-  configCards,
-  searchQuery,
-  setSearchQuery,
-  isLoadingConfigs,
-  hasMoreConfigs,
-  nextConfigSkip,
-  expandedConfigId,
-  versionStateByConfig,
-  latestModelByConfig,
-  loadingSelectionKeys,
-  isSelected,
-  onLoadMoreConfigs,
-  onLoadVersions,
-  onToggleConfigExpansion,
-  onToggleVersionSelection,
   currentProvider,
   currentModel,
   providerModels,
@@ -35,6 +12,13 @@ export default function AssessmentConfiguration({
   configName,
   commitMessage,
   isSaving,
+  isSaveModalOpen,
+  setIsSaveModalOpen,
+  saveMode,
+  setSaveMode,
+  versionConfigId,
+  setVersionConfigId,
+  existingConfigs,
   setConfigName,
   setCommitMessage,
   onProviderChange,
@@ -47,73 +31,38 @@ export default function AssessmentConfiguration({
       <summary className="flex cursor-pointer items-center justify-between px-4 py-3">
         <div>
           <div className="text-sm font-semibold text-text-primary">
-            AI Configuration
+            Model Selection
           </div>
           <div className="mt-1 text-xs text-text-secondary">
-            {configs.length > 0
-              ? `${configs.length} selected`
-              : "Choose at least one configuration"}
+            Choose the provider and model this configuration runs on.
           </div>
         </div>
       </summary>
 
-      {configs.length > 0 && (
-        <div className="border-t border-border px-4 py-4">
-          <SelectedConfigs configs={configs} onRemove={onRemoveConfig} />
-        </div>
-      )}
-
       <div className="border-t border-border px-4 py-4">
-        <div className="mb-4">
-          <RadioGroup<ConfigMode>
-            value={configMode}
-            onChange={setConfigMode}
-            ariaLabel="Config source"
-            options={[
-              { value: "existing", label: "Saved" },
-              { value: "create", label: "New" },
-            ]}
-          />
-        </div>
-
-        {configMode === "existing" && (
-          <SavedConfigs
-            configCards={configCards}
-            searchQuery={searchQuery}
-            setSearchQuery={setSearchQuery}
-            isLoadingConfigs={isLoadingConfigs}
-            hasMoreConfigs={hasMoreConfigs}
-            nextConfigSkip={nextConfigSkip}
-            expandedConfigId={expandedConfigId}
-            versionStateByConfig={versionStateByConfig}
-            latestModelByConfig={latestModelByConfig}
-            loadingSelectionKeys={loadingSelectionKeys}
-            isSelected={isSelected}
-            onLoadMoreConfigs={onLoadMoreConfigs}
-            onLoadVersions={onLoadVersions}
-            onToggleConfigExpansion={onToggleConfigExpansion}
-            onToggleVersionSelection={onToggleVersionSelection}
-          />
-        )}
-
-        {configMode === "create" && (
-          <ConfigCreator
-            currentProvider={currentProvider}
-            currentModel={currentModel}
-            providerModels={providerModels}
-            currentParamDefs={currentParamDefs}
-            draftParams={draftParams}
-            configName={configName}
-            commitMessage={commitMessage}
-            isSaving={isSaving}
-            setConfigName={setConfigName}
-            setCommitMessage={setCommitMessage}
-            onProviderChange={onProviderChange}
-            onModelChange={onModelChange}
-            onParamChange={onParamChange}
-            onSave={onSaveConfig}
-          />
-        )}
+        <ConfigCreator
+          currentProvider={currentProvider}
+          currentModel={currentModel}
+          providerModels={providerModels}
+          currentParamDefs={currentParamDefs}
+          draftParams={draftParams}
+          configName={configName}
+          commitMessage={commitMessage}
+          isSaving={isSaving}
+          isSaveModalOpen={isSaveModalOpen}
+          setIsSaveModalOpen={setIsSaveModalOpen}
+          saveMode={saveMode}
+          setSaveMode={setSaveMode}
+          versionConfigId={versionConfigId}
+          setVersionConfigId={setVersionConfigId}
+          existingConfigs={existingConfigs}
+          setConfigName={setConfigName}
+          setCommitMessage={setCommitMessage}
+          onProviderChange={onProviderChange}
+          onModelChange={onModelChange}
+          onParamChange={onParamChange}
+          onSave={onSaveConfig}
+        />
       </div>
     </details>
   );
diff --git a/app/components/assessment/prompt-config/ConfigCreator.tsx b/app/components/assessment/prompt-config/ConfigCreator.tsx
index 524f9d58..605fdedd 100644
--- a/app/components/assessment/prompt-config/ConfigCreator.tsx
+++ b/app/components/assessment/prompt-config/ConfigCreator.tsx
@@ -1,6 +1,11 @@
-import { Button, Field, Select } from "@/app/components/ui";
+"use client";
+
+import { Button, Field, Modal, RadioGroup, Select } from "@/app/components/ui";
 import { PROVIDER_OPTIONS } from "@/app/lib/data/assessmentModels";
-import type { ConfigCreatorProps } from "@/app/lib/types/assessment";
+import type {
+  ConfigCreatorProps,
+  ConfigSaveMode,
+} from "@/app/lib/types/assessment";
 import type { CompletionConfig } from "@/app/lib/types/configs";
 import ConfigParamControl from "./ConfigParamControl";
 
@@ -16,6 +21,13 @@ export default function ConfigCreator({
   configName,
   commitMessage,
   isSaving,
+  isSaveModalOpen,
+  setIsSaveModalOpen,
+  saveMode,
+  setSaveMode,
+  versionConfigId,
+  setVersionConfigId,
+  existingConfigs,
   setConfigName,
   setCommitMessage,
   onProviderChange,
@@ -23,7 +35,14 @@ export default function ConfigCreator({
   onParamChange,
   onSave,
 }: ConfigCreatorProps) {
-  const saveDisabled = isSaving || !configName.trim();
+  const confirmDisabled =
+    isSaving ||
+    (saveMode === "version" ? !versionConfigId : !configName.trim());
+
+  const handleConfirm = () => {
+    void onSave();
+    setIsSaveModalOpen(false);
+  };
 
   return (
     <div className="space-y-4">
@@ -87,29 +106,73 @@ export default function ConfigCreator({
         </div>
       </details>
 
-      <div className="grid gap-3">
-        <Field
-          label="AI Configuration Name"
-          value={configName}
-          onChange={setConfigName}
-          placeholder="Helpful grader"
-        />
-        <Field
-          label="Save note"
-          value={commitMessage}
-          onChange={setCommitMessage}
-          placeholder="Optional"
-        />
-      </div>
-
-      <Button
-        type="button"
-        fullWidth
-        onClick={() => void onSave()}
-        disabled={saveDisabled}
+      <Modal
+        open={isSaveModalOpen}
+        onClose={() => setIsSaveModalOpen(false)}
+        title="Save configuration"
+        maxWidth="max-w-md"
+        maxHeight="max-h-[90vh]"
       >
-        {isSaving ? "Saving..." : "Save behavior"}
-      </Button>
+        <div className="grid gap-3 px-6 pb-2">
+          <RadioGroup<ConfigSaveMode>
+            value={saveMode}
+            onChange={setSaveMode}
+            ariaLabel="Save mode"
+            options={[
+              { value: "new", label: "New configuration" },
+              { value: "version", label: "New version of existing" },
+            ]}
+          />
+
+          {saveMode === "new" ? (
+            <Field
+              label="AI Configuration Name"
+              value={configName}
+              onChange={setConfigName}
+              placeholder="Helpful grader"
+            />
+          ) : (
+            <div>
+              <label className="mb-2 block text-xs font-semibold text-text-primary">
+                Existing configuration
+              </label>
+              <Select
+                value={versionConfigId}
+                placeholder="Select a configuration"
+                options={existingConfigs.map((config) => ({
+                  value: config.id,
+                  label: config.name,
+                }))}
+                onChange={(event) => setVersionConfigId(event.target.value)}
+                className={selectClass}
+              />
+            </div>
+          )}
+
+          <Field
+            label="Save note"
+            value={commitMessage}
+            onChange={setCommitMessage}
+            placeholder="Optional"
+          />
+        </div>
+        <div className="flex items-center justify-end gap-3 border-t border-border px-6 py-4">
+          <Button
+            type="button"
+            variant="outline"
+            onClick={() => setIsSaveModalOpen(false)}
+          >
+            Cancel
+          </Button>
+          <Button
+            type="button"
+            onClick={handleConfirm}
+            disabled={confirmDisabled}
+          >
+            {isSaving ? "Saving..." : "Save"}
+          </Button>
+        </div>
+      </Modal>
     </div>
   );
 }
diff --git a/app/components/assessment/prompt-config/PromptEditor.tsx b/app/components/assessment/prompt-config/PromptEditor.tsx
index 93b86d9f..34bbb380 100644
--- a/app/components/assessment/prompt-config/PromptEditor.tsx
+++ b/app/components/assessment/prompt-config/PromptEditor.tsx
@@ -2,7 +2,7 @@
 
 import { Button } from "@/app/components/ui";
 import { usePromptPlaceholderEditor } from "@/app/hooks/usePromptPlaceholderEditor";
-import type { SampleRow, ValueSetter } from "@/app/lib/types/assessment";
+import type { ValueSetter } from "@/app/lib/types/assessment";
 
 interface PromptEditorProps {
   value: string;
@@ -11,7 +11,6 @@ interface PromptEditorProps {
   placeholder: string;
   emptyPreviewText: string;
   textColumns?: string[];
-  sampleRow?: SampleRow;
   enablePlaceholders?: boolean;
 }
 
@@ -22,7 +21,6 @@ export default function PromptEditor({
   placeholder,
   emptyPreviewText,
   textColumns = [],
-  sampleRow = {},
   enablePlaceholders = true,
 }: PromptEditorProps) {
   const {
@@ -37,33 +35,24 @@ export default function PromptEditor({
     handleInput,
     handleKeyDown,
     insertMention,
-    insertPlaceholder,
-    usedColumns,
-    orderedColumns,
     previewText,
   } = usePromptPlaceholderEditor({
     value,
     onChange,
     previewMode,
-    textColumns,
-    sampleRow,
+    // Drop blank/whitespace column names so no empty `{}` placeholder or
+    // duplicate-empty-key mention option is ever produced.
+    textColumns: textColumns.filter((col) => col.trim() !== ""),
     enablePlaceholders,
   });
 
   if (previewMode) {
     return (
       <div className="h-[260px] overflow-y-auto whitespace-pre-wrap break-words rounded-xl border border-border bg-bg-secondary px-4 py-3 text-sm leading-7 text-text-primary">
-        {!value.trim() ? (
-          <span className="text-text-secondary">{emptyPreviewText}</span>
-        ) : enablePlaceholders && Object.keys(sampleRow).length === 0 ? (
-          <span className="text-text-secondary">
-            Sample data not available. Go back to Datasets and choose a row with
-            values.
-          </span>
+        {previewText ? (
+          previewText
         ) : (
-          previewText || (
-            <span className="text-text-secondary">{emptyPreviewText}</span>
-          )
+          <span className="text-text-secondary">{emptyPreviewText}</span>
         )}
       </div>
     );
@@ -72,31 +61,10 @@ export default function PromptEditor({
   return (
     <>
       {enablePlaceholders && (
-        <div className="mb-3">
-          <div className="mb-2 text-xs text-text-secondary">
-            Use `@` or tap a column chip to insert placeholders.
-          </div>
-          <div className="flex flex-wrap gap-2">
-            {orderedColumns.map((col) => {
-              const isUsed = usedColumns.includes(col);
-              return (
-                <Button
-                  key={col}
-                  type="button"
-                  variant={isUsed ? "secondary" : "outline"}
-                  size="sm"
-                  onClick={() => insertPlaceholder(col)}
-                  className={`!rounded-full !px-3 !py-1.5 !font-mono !text-xs ${
-                    isUsed
-                      ? "!border-status-success-border !bg-status-success-bg !text-status-success-text"
-                      : "!bg-bg-primary"
-                  }`}
-                >
-                  {`{${col}}`}
-                </Button>
-              );
-            })}
-          </div>
+        <div className="mb-2 text-xs text-text-secondary">
+          Type <span className="font-mono">@</span> to mention a column and
+          insert it as a <span className="font-mono">{"{column}"}</span>{" "}
+          placeholder.
         </div>
       )}
 
diff --git a/app/components/assessment/prompt-config/PromptPanel.tsx b/app/components/assessment/prompt-config/PromptPanel.tsx
index 1c96ec3f..fe91f9a0 100644
--- a/app/components/assessment/prompt-config/PromptPanel.tsx
+++ b/app/components/assessment/prompt-config/PromptPanel.tsx
@@ -1,49 +1,18 @@
 "use client";
 
-import { useState } from "react";
-import { RadioGroup } from "@/app/components/ui";
 import type { PromptPanelProps } from "@/app/lib/types/assessment";
-
-type PromptViewMode = "edit" | "preview";
-import UserPrompt from "./UserPrompt";
 import SystemPrompt from "./SystemPrompt";
 
 export default function PromptPanel({
-  textColumns,
-  sampleRow,
   systemInstruction,
   setSystemInstruction,
-  promptTemplate,
-  setPromptTemplate,
 }: PromptPanelProps) {
-  const [viewMode, setViewMode] = useState<PromptViewMode>("edit");
-  const previewMode = viewMode === "preview";
-
   return (
     <section className="min-w-0 space-y-4">
-      <div className="flex justify-end">
-        <RadioGroup<PromptViewMode>
-          value={viewMode}
-          onChange={setViewMode}
-          ariaLabel="Prompt view mode"
-          options={[
-            { value: "edit", label: "Edit" },
-            { value: "preview", label: "Preview" },
-          ]}
-        />
-      </div>
-
       <SystemPrompt
         value={systemInstruction}
         onChange={setSystemInstruction}
-        previewMode={previewMode}
-      />
-      <UserPrompt
-        textColumns={textColumns}
-        sampleRow={sampleRow}
-        promptTemplate={promptTemplate}
-        setPromptTemplate={setPromptTemplate}
-        previewMode={previewMode}
+        previewMode={false}
       />
     </section>
   );
diff --git a/app/components/assessment/prompt-config/SystemPrompt.tsx b/app/components/assessment/prompt-config/SystemPrompt.tsx
index 596cbc2c..f77944b3 100644
--- a/app/components/assessment/prompt-config/SystemPrompt.tsx
+++ b/app/components/assessment/prompt-config/SystemPrompt.tsx
@@ -39,7 +39,7 @@ export default function SystemPrompt({
         <InfoTooltip
           text={
             <span>
-              Set the evaluation rules. Example: judge every answer fairly,
+              Set the assessment rules. Example: judge every answer fairly,
               follow the scoring format, and explain the result briefly.
             </span>
           }
diff --git a/app/components/assessment/prompt-config/UserPrompt.tsx b/app/components/assessment/prompt-config/UserPrompt.tsx
index 1c5101ae..1392bf42 100644
--- a/app/components/assessment/prompt-config/UserPrompt.tsx
+++ b/app/components/assessment/prompt-config/UserPrompt.tsx
@@ -3,12 +3,11 @@
 import { useState } from "react";
 import { Button, InfoTooltip } from "@/app/components/ui";
 import { ChevronDownIcon } from "@/app/components/icons";
-import type { SampleRow, ValueSetter } from "@/app/lib/types/assessment";
+import type { ValueSetter } from "@/app/lib/types/assessment";
 import PromptEditor from "./PromptEditor";
 
 interface UserPromptProps {
   textColumns: string[];
-  sampleRow: SampleRow;
   promptTemplate: string;
   setPromptTemplate: ValueSetter<string>;
   previewMode: boolean;
@@ -16,7 +15,6 @@ interface UserPromptProps {
 
 export default function UserPrompt({
   textColumns,
-  sampleRow,
   promptTemplate,
   setPromptTemplate,
   previewMode,
@@ -62,7 +60,6 @@ export default function UserPrompt({
             onChange={setPromptTemplate}
             previewMode={previewMode}
             textColumns={textColumns}
-            sampleRow={sampleRow}
             enablePlaceholders
             emptyPreviewText="Preview will appear here."
             placeholder={`Describe what the AI should do.\n\nExample:\nEvaluate the student's answer.\nQuestion: {question}\nAnswer: {answer}\nContext: {context}`}
diff --git a/app/components/assessment/review/ExperimentReview.tsx b/app/components/assessment/review/ExperimentReview.tsx
index 8ed347fb..b7ad6ff9 100644
--- a/app/components/assessment/review/ExperimentReview.tsx
+++ b/app/components/assessment/review/ExperimentReview.tsx
@@ -22,7 +22,7 @@ export default function ExperimentReview({
         className="!rounded-md !bg-neutral-50 !px-3 !py-2"
       />
       <p className="mt-1.5 text-[11px] text-neutral-500">
-        A descriptive name to identify this evaluation run.
+        A descriptive name to identify this assessment run.
       </p>
     </div>
   );
diff --git a/app/components/assessment/review/PrefilterReview.tsx b/app/components/assessment/review/PrefilterReview.tsx
index 542d4e0b..f8218711 100644
--- a/app/components/assessment/review/PrefilterReview.tsx
+++ b/app/components/assessment/review/PrefilterReview.tsx
@@ -38,7 +38,7 @@ export default function PrefilterReview({
 
   return (
     <ReviewSection
-      title="Eliminatory"
+      title="Pre-filter"
       isOpen={isOpen}
       onToggle={onToggle}
       onEdit={onEdit}
diff --git a/app/components/assessment/review/SubmitReview.tsx b/app/components/assessment/review/SubmitReview.tsx
index defde80f..7c392e6b 100644
--- a/app/components/assessment/review/SubmitReview.tsx
+++ b/app/components/assessment/review/SubmitReview.tsx
@@ -53,7 +53,7 @@ export default function SubmitReview({
             ) : (
               <>
                 <PlayIcon className="h-5 w-5" />
-                Submit Evaluation
+                Submit Assessment
               </>
             )}
           </Button>
diff --git a/app/hooks/useAssessmentDatasetsTab.ts b/app/hooks/useAssessmentDatasetsTab.ts
index 319f3281..f37dc184 100644
--- a/app/hooks/useAssessmentDatasetsTab.ts
+++ b/app/hooks/useAssessmentDatasetsTab.ts
@@ -10,36 +10,31 @@ import {
   fetchDatasetPreview,
   handleForbiddenError,
   isAllowedDatasetFile,
-  isBlankCell,
 } from "@/app/lib/utils/assessment";
 import { PREVIEW_ROW_LIMIT } from "@/app/lib/assessment/results";
-import {
-  DATASET_SAMPLE_ROW_LIMIT,
-  MAX_DATASET_FILE_BYTES,
-} from "@/app/lib/assessment/constants";
+import { MAX_DATASET_FILE_BYTES } from "@/app/lib/assessment/constants";
 import type {
   CreateDatasetResponse,
   DatasetPreview,
   DatasetResponse,
-  DatasetsTabProps,
   DatasetViewModalData,
+  ValueSetter,
+  WithForbiddenHandler,
 } from "@/app/lib/types/assessment";
 
-type UseAssessmentDatasetsTabParams = Pick<
-  DatasetsTabProps,
-  | "onForbidden"
-  | "datasetId"
-  | "setDatasetId"
-  | "setSelectedDatasetName"
-  | "onColumnsLoaded"
->;
+// Shared by the Datasets tab (library management) and the Experiment tab
+// (dataset selection at run time). Selection only records the dataset id/name;
+// the run's input_binding is derived from the chosen config's input_schema.
+interface UseAssessmentDatasetsTabParams extends WithForbiddenHandler {
+  datasetId: string;
+  setDatasetId: ValueSetter<string>;
+  setSelectedDatasetName: ValueSetter<string>;
+}
 
 export interface UseAssessmentDatasetsTabResult {
   datasets: Dataset[];
   isLoading: boolean;
-  isLoadingColumns: boolean;
   viewingId: number | null;
-  canProceed: boolean;
   datasetName: string;
   datasetDescription: string;
   uploadedFile: File | null;
@@ -59,7 +54,7 @@ export interface UseAssessmentDatasetsTabResult {
   handleFileSelect: (event: React.ChangeEvent<HTMLInputElement>) => void;
   resetForm: () => void;
   handleCreateDataset: () => Promise<void>;
-  handleDatasetSelect: (id: string, name?: string) => Promise<void>;
+  handleDatasetSelect: (id: string, name?: string) => void;
   handleViewDataset: (datasetId: number, name: string) => Promise<void>;
   handleDeleteDataset: (id: number) => Promise<void>;
   handleDrop: (event: React.DragEvent<HTMLDivElement>) => void;
@@ -70,7 +65,6 @@ export function useAssessmentDatasetsTab({
   datasetId,
   setDatasetId,
   setSelectedDatasetName,
-  onColumnsLoaded,
 }: UseAssessmentDatasetsTabParams): UseAssessmentDatasetsTabResult {
   const toast = useToast();
   const { activeKey, isAuthenticated } = useAuth();
@@ -79,7 +73,6 @@ export function useAssessmentDatasetsTab({
 
   const [datasets, setDatasets] = useState<Dataset[]>([]);
   const [isLoading, setIsLoading] = useState(false);
-  const [isLoadingColumns, setIsLoadingColumns] = useState(false);
   const [datasetName, setDatasetName] = useState("");
   const [datasetDescription, setDatasetDescription] = useState("");
   const [uploadedFile, setUploadedFile] = useState<File | null>(null);
@@ -156,58 +149,20 @@ export function useAssessmentDatasetsTab({
     if (fileInputRef.current) fileInputRef.current.value = "";
   };
 
-  const handleDatasetSelect = async (id: string, name?: string) => {
+  // Records which dataset a run targets; no column loading — the run's
+  // input_binding comes from the selected config's input_schema.
+  const handleDatasetSelect = (id: string, name?: string) => {
     setDatasetId(id);
     if (!id) {
       setSelectedDatasetName("");
-      onColumnsLoaded([]);
       return;
     }
-
     const resolvedName =
       name ??
       datasets.find((dataset) => dataset.dataset_id.toString() === id)
         ?.dataset_name ??
       "";
     setSelectedDatasetName(resolvedName);
-
-    setIsLoadingColumns(true);
-    try {
-      const cached = previewCache[id];
-      const parsed =
-        cached ??
-        (await fetchDatasetPreview(id, apiKey, DATASET_SAMPLE_ROW_LIMIT));
-      if (!cached) {
-        setPreviewCache((prev) => ({ ...prev, [id]: parsed }));
-      }
-      const keptIdx = parsed.headers
-        .map((_, colIdx) => colIdx)
-        .filter((colIdx) =>
-          parsed.rows.some((row) => !isBlankCell(row[colIdx])),
-        );
-
-      const filteredHeaders = keptIdx.map((idx) => parsed.headers[idx]);
-      const firstRow = parsed.rows[0] || [];
-      const sampleRow = Object.fromEntries(
-        keptIdx.map((idx) => [
-          parsed.headers[idx],
-          String(firstRow[idx] ?? ""),
-        ]),
-      );
-      onColumnsLoaded(filteredHeaders, sampleRow);
-    } catch (error) {
-      if (handleForbiddenError(error, onForbidden)) return;
-      const message =
-        error instanceof Error
-          ? error.message
-          : "Failed to fetch dataset columns.";
-      onColumnsLoaded([]);
-      setDatasetId("");
-      setSelectedDatasetName("");
-      toast.error(message);
-    } finally {
-      setIsLoadingColumns(false);
-    }
   };
 
   const handleCreateDataset = async () => {
@@ -323,7 +278,6 @@ export function useAssessmentDatasetsTab({
     fileInputRef.current.dispatchEvent(new Event("change", { bubbles: true }));
   };
 
-  const canProceed = Boolean(datasetId) && !isLoadingColumns;
   const datasetPendingDelete = datasets.find(
     (dataset) => dataset.dataset_id === confirmDeleteId,
   );
@@ -331,9 +285,7 @@ export function useAssessmentDatasetsTab({
   return {
     datasets,
     isLoading,
-    isLoadingColumns,
     viewingId,
-    canProceed,
     datasetName,
     datasetDescription,
     uploadedFile,
diff --git a/app/hooks/useAssessmentWorkflow.ts b/app/hooks/useAssessmentWorkflow.ts
index 10e8ce30..f45466d7 100644
--- a/app/hooks/useAssessmentWorkflow.ts
+++ b/app/hooks/useAssessmentWorkflow.ts
@@ -9,29 +9,61 @@ import {
   getAssessmentSubmitBlocker,
   getAssessmentSubmitError,
   handleForbiddenError,
-  schemaToJsonSchema,
 } from "@/app/lib/utils/assessment";
 import { removeFeatureFromClient } from "@/app/lib/utils/features";
 import { FeatureFlag } from "@/app/lib/constants";
-import { PAGE_TABS } from "@/app/lib/assessment/constants";
+import {
+  ASSESSMENT_TAB_ROUTES,
+  PAGE_TABS,
+} from "@/app/lib/assessment/constants";
 import { useAssessmentDatasetStore } from "@/app/lib/store/assessment";
+import { assessmentBlobToBuilderState } from "@/app/lib/utils/assessmentFetcher";
 import type {
-  AssessmentFormState,
+  AssessmentRunConfigRef,
   AssessmentTabId,
+  ColumnMapping,
+  ConfigDraftSeed,
   ConfigSelection,
   PageLayoutProps,
   PrefilterConfig,
   PostProcessingConfig,
   SchemaProperty,
 } from "@/app/lib/types/assessment";
+import type {
+  AssessmentColumnType,
+  AssessmentConfigBlob,
+} from "@/app/lib/types/configs";
+
+const EMPTY_COLUMN_MAPPING: ColumnMapping = {
+  textColumns: [],
+  attachments: [],
+  groundTruthColumns: [],
+};
 
 export type UseAssessmentWorkflowResult = PageLayoutProps;
 
-export function useAssessmentWorkflow(): UseAssessmentWorkflowResult {
+export function useAssessmentWorkflow(
+  initialTab: AssessmentTabId = "datasets",
+): UseAssessmentWorkflowResult {
   const router = useRouter();
   const { error: showToastError, success: showToastSuccess } = useToast();
   const { activeKey } = useAuth();
-  const [activeTab, setActiveTab] = useState<AssessmentTabId>("datasets");
+  const [activeTab, setActiveTab] = useState<AssessmentTabId>(initialTab);
+
+  // The route (sidebar sub-tab) is the source of truth; keep state in sync when
+  // the page mounts/remounts on a different route.
+  useEffect(() => {
+    setActiveTab(initialTab);
+  }, [initialTab]);
+
+  // Switch tab AND navigate so the sidebar sub-item highlights.
+  const goToTab = useCallback(
+    (tab: AssessmentTabId) => {
+      setActiveTab(tab);
+      router.push(ASSESSMENT_TAB_ROUTES[tab]);
+    },
+    [router],
+  );
   const [configStep, setConfigStep] = useState(1);
   const [completedConfigSteps, setCompletedConfigSteps] = useState<Set<number>>(
     new Set(),
@@ -39,18 +71,12 @@ export function useAssessmentWorkflow(): UseAssessmentWorkflowResult {
   const [isSubmitting, setIsSubmitting] = useState(false);
   const [experimentName, setExperimentName] = useState("");
   const featureRedirectingRef = useRef(false);
-  const {
-    datasetId,
-    datasetName,
-    columns,
-    sampleRow,
-    columnMapping,
-    setDatasetId,
-    setDatasetName,
-    setDataset,
-    setColumnMapping,
-    clearDataset,
-  } = useAssessmentDatasetStore();
+  const { datasetId, datasetName, setDatasetId, setDatasetName, clearDataset } =
+    useAssessmentDatasetStore();
+  // Config input_schema is authored directly (dataset-independent) via the
+  // manual field editor, so the mapping starts empty and lives in the workflow.
+  const [columnMapping, setColumnMapping] =
+    useState<ColumnMapping>(EMPTY_COLUMN_MAPPING);
   const [promptTemplate, setPromptTemplate] = useState("");
   const [systemInstruction, setSystemInstruction] = useState("");
   const [outputSchema, setOutputSchema] = useState<SchemaProperty[]>([]);
@@ -59,6 +85,45 @@ export function useAssessmentWorkflow(): UseAssessmentWorkflowResult {
     useState<PrefilterConfig | null>(null);
   const [postProcessingConfig, setPostProcessingConfig] =
     useState<PostProcessingConfig | null>(null);
+  // Seeds the Assessment step's provider/model draft + save mode when the
+  // Configuration step starts fresh or loads an existing version.
+  const [configSeed, setConfigSeed] = useState<ConfigDraftSeed | null>(null);
+  const seedNonce = useRef(0);
+
+  const startNewConfig = useCallback(() => {
+    setColumnMapping(EMPTY_COLUMN_MAPPING);
+    setSystemInstruction("");
+    setPromptTemplate("");
+    setOutputSchema([]);
+    setPrefilterConfig(null);
+    seedNonce.current += 1;
+    setConfigSeed({
+      blob: null,
+      saveMode: "new",
+      configId: "",
+      configName: "",
+      nonce: seedNonce.current,
+    });
+  }, []);
+
+  const loadExistingConfig = useCallback(
+    (blob: AssessmentConfigBlob, configId: string, configName: string) => {
+      const state = assessmentBlobToBuilderState(blob);
+      setColumnMapping(state.columnMapping);
+      setSystemInstruction(state.systemInstruction);
+      setOutputSchema(state.outputSchema);
+      setPrefilterConfig(state.prefilterConfig);
+      seedNonce.current += 1;
+      setConfigSeed({
+        blob: state.draft,
+        saveMode: "version",
+        configId,
+        configName,
+        nonce: seedNonce.current,
+      });
+    },
+    [],
+  );
 
   const handleForbidden = useCallback(
     (options?: { notify?: boolean }) => {
@@ -98,33 +163,19 @@ export function useAssessmentWorkflow(): UseAssessmentWorkflowResult {
     [markConfigCompleted],
   );
 
-  const handleColumnsLoaded = useCallback(
-    (loadedColumns: string[], firstRow: Record<string, string> = {}) => {
-      const currentId = useAssessmentDatasetStore.getState().datasetId;
-      setDataset(currentId, loadedColumns, firstRow);
-      setPromptTemplate("");
-    },
-    [setDataset],
-  );
-
-  useEffect(() => {
-    setPrefilterConfig(null);
-  }, [datasetId]);
-
-  const outputSchemaJson = useMemo(
-    () => schemaToJsonSchema(outputSchema),
-    [outputSchema],
-  );
+  // input_binding is derived from the selected config's stored input_schema so a
+  // saved config can run without re-authoring: text-typed keys become
+  // text_columns, image/pdf keys become url attachments.
+  const runInputSchema = configs[0]?.input_schema ?? {};
 
   const handleSubmit = useCallback(async () => {
+    const inputSchemaEntries = Object.entries(runInputSchema);
     const validationError = getAssessmentSubmitError({
       datasetId,
-      hasMapperSelection:
-        columnMapping.textColumns.length > 0 ||
-        columnMapping.attachments.length > 0,
-      hasResponseFormat: outputSchema.some((field) => field.name.trim()),
+      hasInputSchema: inputSchemaEntries.length > 0,
       configCount: configs.length,
       experimentName,
+      hasPrompt: promptTemplate.trim().length > 0,
     });
     if (validationError) {
       showToastError(validationError);
@@ -133,28 +184,35 @@ export function useAssessmentWorkflow(): UseAssessmentWorkflowResult {
 
     setIsSubmitting(true);
     try {
+      const runConfigs: AssessmentRunConfigRef[] = configs.map(
+        ({ config_id, config_version }) => ({
+          id: config_id,
+          version: config_version,
+        }),
+      );
+      const textColumns = inputSchemaEntries
+        .filter(([, column]) => column.type === "text")
+        .map(([name]) => name);
+      const attachments = inputSchemaEntries
+        .filter(([, column]) => column.type !== "text")
+        .map(([name, column]) => ({
+          column: name,
+          type: column.type as Exclude<AssessmentColumnType, "text">,
+          format: column.format ?? "url",
+        }));
       await apiFetch("/api/assessment/runs", activeKey?.key ?? "", {
         method: "POST",
         body: JSON.stringify({
           experiment_name: experimentName.trim(),
           dataset_id: parseInt(datasetId, 10),
-          prompt_template: promptTemplate || null,
-          system_instruction: systemInstruction.trim() || null,
-          text_columns: columnMapping.textColumns,
-          attachments: columnMapping.attachments.map(
-            ({ column, type, format, type_column, type_value_map }) => ({
-              column,
-              type,
-              format,
-              ...(type_column ? { type_column, type_value_map } : {}),
-            }),
-          ),
-          output_schema: outputSchemaJson,
-          configs: configs.map(({ config_id, config_version }) => ({
-            config_id,
-            config_version,
-          })),
-          prefilter_config: prefilterConfig ?? null,
+          input_binding: {
+            // Authored in the Experiment run step (not stored in the config);
+            // required non-empty because the legacy binding needs min_length 1.
+            prompt: promptTemplate,
+            text_columns: textColumns,
+            attachments,
+          },
+          configs: runConfigs,
           post_processing_config: postProcessingConfig ?? null,
         }),
       });
@@ -164,13 +222,15 @@ export function useAssessmentWorkflow(): UseAssessmentWorkflowResult {
       setCompletedConfigSteps(new Set());
       setExperimentName("");
       clearDataset();
+      setColumnMapping(EMPTY_COLUMN_MAPPING);
       setSystemInstruction("");
       setPromptTemplate("");
       setOutputSchema([]);
       setConfigs([]);
       setPrefilterConfig(null);
+      setConfigSeed(null);
       setPostProcessingConfig(null);
-      setActiveTab("results");
+      goToTab("results");
     } catch (error) {
       if (handleForbiddenError(error, handleForbiddenWithNotify)) return;
       showToastError(
@@ -181,38 +241,21 @@ export function useAssessmentWorkflow(): UseAssessmentWorkflowResult {
     }
   }, [
     clearDataset,
-    columnMapping,
     configs,
     datasetId,
     experimentName,
+    goToTab,
     handleForbiddenWithNotify,
-    prefilterConfig,
-    outputSchema,
-    outputSchemaJson,
     postProcessingConfig,
     promptTemplate,
+    runInputSchema,
     activeKey,
-    systemInstruction,
     showToastError,
     showToastSuccess,
   ]);
 
-  const formState: AssessmentFormState = {
-    experimentName,
-    datasetId,
-    datasetName,
-    columns,
-    sampleRow,
-    columnMapping,
-    systemInstruction,
-    promptTemplate,
-    outputSchema,
-    configs,
-    prefilterConfig,
-    postProcessingConfig,
-  };
-
-  const hasDataset = !!datasetId && columns.length > 0;
+  // Config-authoring progress indicators (Mapper builds input fields, Evaluation
+  // sets the response format).
   const hasMapperSelection =
     columnMapping.textColumns.length > 0 ||
     columnMapping.attachments.length > 0;
@@ -220,75 +263,88 @@ export function useAssessmentWorkflow(): UseAssessmentWorkflowResult {
     field.name.trim(),
   );
   const canReachReview = configs.length > 0 && hasConfiguredResponseFormat;
+
+  // Run readiness is driven by the selected config's stored input_schema.
+  const hasRunInputSchema = Object.keys(runInputSchema).length > 0;
+  const hasRunPrompt = promptTemplate.trim().length > 0;
   const canSubmitAssessment =
     !!datasetId &&
-    hasMapperSelection &&
-    hasConfiguredResponseFormat &&
     configs.length > 0 &&
+    hasRunInputSchema &&
     experimentName.trim().length > 0 &&
+    hasRunPrompt &&
     !isSubmitting;
   const submitBlockerMessage = getAssessmentSubmitBlocker({
     datasetId,
-    hasMapperSelection,
-    hasResponseFormat: hasConfiguredResponseFormat,
+    hasInputSchema: hasRunInputSchema,
     configCount: configs.length,
     experimentName,
+    hasPrompt: hasRunPrompt,
   });
   const effectiveCompletedConfigSteps = useMemo(() => {
+    // Steps: 1 Configuration, 2 Input Schema, 3 Pre-filter (optional), 4 Assessment.
     const merged = new Set(completedConfigSteps);
-    if (hasMapperSelection) merged.add(1);
-    if (hasMapperSelection) merged.add(2); // Prefilter is optional and always passable
-    if (canReachReview) merged.add(3);
-    if (canReachReview) merged.add(4); // Post Processing is optional and always passable
+    if (hasMapperSelection) {
+      merged.add(2);
+      merged.add(3); // Pre-filter is optional and always passable
+    }
+    if (canReachReview) merged.add(4);
     return merged;
   }, [canReachReview, completedConfigSteps, hasMapperSelection]);
 
   return {
     activeTab,
     tabs: [...PAGE_TABS],
-    onTabSwitch: setActiveTab,
+    onTabSwitch: goToTab,
     datasetsTabProps: {
       onForbidden: handleForbiddenWithNotify,
       datasetId,
       setDatasetId,
       setSelectedDatasetName: setDatasetName,
-      onColumnsLoaded: handleColumnsLoaded,
-      onNext: () => {
-        setActiveTab("config");
-        setConfigStep(1);
-      },
     },
     configPanelProps: {
-      canSubmitAssessment,
-      columns,
       columnMapping,
       completedSteps: effectiveCompletedConfigSteps,
       configStep,
       configs,
-      datasetId,
-      experimentName,
-      formState,
-      hasDataset,
-      isSubmitting,
       prefilterConfig,
       outputSchema,
       systemInstruction,
       promptTemplate,
-      sampleRow,
-      setActiveTabToDatasets: () => setActiveTab("datasets"),
       setColumnMapping,
       setConfigStep,
       setConfigs,
-      setExperimentName,
       setPrefilterConfig,
       setOutputSchema,
       setSystemInstruction,
       setPromptTemplate,
-      postProcessingConfig,
-      setPostProcessingConfig,
+      onStepComplete: handleConfigNext,
+      configSeed,
+      onStartNewConfig: startNewConfig,
+      onLoadExistingConfig: loadExistingConfig,
+      onForbidden: handleForbiddenWithNotify,
+    },
+    experimentTabProps: {
+      onForbidden: handleForbiddenWithNotify,
+      textColumns: columnMapping.textColumns,
+      promptTemplate,
+      setPromptTemplate,
+      configs,
+      setConfigs,
+      outputSchema,
+      systemInstruction,
+      columnMapping,
+      prefilterConfig,
+      datasetId,
+      datasetName,
+      setDatasetId,
+      setSelectedDatasetName: setDatasetName,
+      experimentName,
+      setExperimentName,
+      isSubmitting,
+      canSubmit: canSubmitAssessment,
       submitBlockerMessage,
       onSubmit: handleSubmit,
-      onStepComplete: handleConfigNext,
     },
     evaluationsTabProps: {
       onForbidden: handleForbiddenWithNotify,
diff --git a/app/hooks/useConfigRunDetails.ts b/app/hooks/useConfigRunDetails.ts
index f742e0fc..759f058e 100644
--- a/app/hooks/useConfigRunDetails.ts
+++ b/app/hooks/useConfigRunDetails.ts
@@ -8,6 +8,7 @@ import {
 } from "@/app/lib/utils/assessment";
 import { ASSESSMENT_TAG } from "@/app/lib/assessment/constants";
 import type {
+  AssessmentConfigBlob,
   ConfigResponse,
   ConfigVersionResponse,
 } from "@/app/lib/types/configs";
@@ -83,16 +84,16 @@ export default function useConfigRunDetails({
           );
         }
 
+        const assessmentBlob = versionResponse.data
+          .config_blob as unknown as AssessmentConfigBlob | null;
         const detail: ConfigRunDetail = {
           configId,
           version,
           name: configResponse.data.name,
           description: configResponse.data.description,
           commitMessage: versionResponse.data.commit_message,
-          provider:
-            versionResponse.data.config_blob?.completion?.provider || null,
-          model:
-            versionResponse.data.config_blob?.completion?.params?.model || null,
+          provider: assessmentBlob?.assessment?.provider || null,
+          model: assessmentBlob?.assessment?.params?.model || null,
         };
 
         setConfigDetailsByKey((prev) => ({ ...prev, [key]: detail }));
diff --git a/app/hooks/usePromptAndConfigStep.ts b/app/hooks/usePromptAndConfigStep.ts
index a65f931d..206d075c 100644
--- a/app/hooks/usePromptAndConfigStep.ts
+++ b/app/hooks/usePromptAndConfigStep.ts
@@ -9,6 +9,7 @@ import {
   MAX_CONFIGS,
 } from "@/app/lib/assessment/constants";
 import {
+  buildAssessmentConfigBlob,
   buildDefaultParams,
   buildInitialAssessmentConfigDraft,
   buildInitialAssessmentVersionState,
@@ -22,21 +23,30 @@ import {
 } from "@/app/lib/utils/assessmentFetcher";
 import {
   type ConfigMode,
+  type ConfigSaveMode,
   type ConfigSelection,
   type PromptAndConfigStepProps,
   type UsePromptAndConfigStepResult,
   type VersionListState,
 } from "@/app/lib/types/assessment";
 import type {
+  AssessmentConfigBlob,
   CompletionConfig,
-  ConfigBlob,
   ConfigPublic,
 } from "@/app/lib/types/configs";
 import useLatestConfigModels from "@/app/hooks/useLatestConfigModels";
 
 type UsePromptAndConfigStepParams = Pick<
   PromptAndConfigStepProps,
-  "textColumns" | "promptTemplate" | "configs" | "setConfigs" | "outputSchema"
+  | "textColumns"
+  | "promptTemplate"
+  | "configs"
+  | "setConfigs"
+  | "outputSchema"
+  | "systemInstruction"
+  | "columnMapping"
+  | "prefilterConfig"
+  | "configSeed"
 >;
 
 export function usePromptAndConfigStep({
@@ -45,6 +55,10 @@ export function usePromptAndConfigStep({
   configs,
   setConfigs,
   outputSchema,
+  systemInstruction,
+  columnMapping,
+  prefilterConfig,
+  configSeed,
 }: UsePromptAndConfigStepParams): UsePromptAndConfigStepResult {
   const toast = useToast();
   const { activeKey, isAuthenticated } = useAuth();
@@ -65,18 +79,32 @@ export function usePromptAndConfigStep({
   >({});
   const hasLoadedInitialConfigsRef = useRef(false);
 
-  const [draft, setDraft] = useState<ConfigBlob>(() =>
+  const [draft, setDraft] = useState<AssessmentConfigBlob>(() =>
     buildInitialAssessmentConfigDraft(),
   );
   const [configName, setConfigName] = useState("");
   const [commitMessage, setCommitMessage] = useState("");
+  const [saveMode, setSaveMode] = useState<ConfigSaveMode>("new");
+  const [versionConfigId, setVersionConfigId] = useState("");
   const [isSaving, setIsSaving] = useState(false);
+  const appliedSeedNonce = useRef<number | null>(null);
 
-  const draftParams = draft.completion.params as Record<
+  // Apply a config seed from the Configuration step once per (re)load: hydrate
+  // the provider/model draft and preset the save mode (new vs new-version).
+  useEffect(() => {
+    if (!configSeed || appliedSeedNonce.current === configSeed.nonce) return;
+    appliedSeedNonce.current = configSeed.nonce;
+    if (configSeed.blob) setDraft(configSeed.blob);
+    setSaveMode(configSeed.saveMode);
+    setVersionConfigId(configSeed.configId);
+    setConfigName(configSeed.configName);
+  }, [configSeed]);
+
+  const draftParams = draft.assessment.params as Record<
     string,
     string | number | undefined
   >;
-  const currentProvider = draft.completion.provider ?? "openai";
+  const currentProvider = draft.assessment.provider ?? "openai";
   const providerModels = useMemo(
     () => getModelsByProvider(currentProvider),
     [currentProvider],
@@ -93,6 +121,17 @@ export function usePromptAndConfigStep({
   );
   const namedSchemaFields = outputSchema.filter((field) => field.name.trim());
   const hasConfiguredResponseFormat = namedSchemaFields.length > 0;
+  const configBlob = useMemo(
+    () =>
+      buildAssessmentConfigBlob({
+        draft,
+        systemInstruction,
+        outputSchema,
+        columnMapping,
+        prefilterConfig,
+      }),
+    [draft, systemInstruction, outputSchema, columnMapping, prefilterConfig],
+  );
   const canProceed = configs.length > 0 && hasConfiguredResponseFormat;
   const nextBlockerMessage =
     configs.length === 0
@@ -288,9 +327,9 @@ export function usePromptAndConfigStep({
   const updateDraftParam = (key: string, value: string | number) => {
     setDraft((prev) => ({
       ...prev,
-      completion: {
-        ...prev.completion,
-        params: { ...prev.completion.params, [key]: value },
+      assessment: {
+        ...prev.assessment,
+        params: { ...prev.assessment.params, [key]: value },
       },
     }));
   };
@@ -299,11 +338,12 @@ export function usePromptAndConfigStep({
     const defaultModel = getDefaultModelForProvider(provider);
     setDraft((prev) => ({
       ...prev,
-      completion: {
-        ...prev.completion,
+      assessment: {
+        ...prev.assessment,
         provider,
         params: {
-          instructions: String(prev.completion.params.instructions || ""),
+          instructions: String(prev.assessment.params.instructions || ""),
+          input_schema: prev.assessment.params.input_schema,
           model: defaultModel,
           ...buildDefaultParams(defaultModel),
         },
@@ -314,10 +354,11 @@ export function usePromptAndConfigStep({
   const handleModelChange = (modelName: string) => {
     setDraft((prev) => ({
       ...prev,
-      completion: {
-        ...prev.completion,
+      assessment: {
+        ...prev.assessment,
         params: {
-          instructions: String(prev.completion.params.instructions || ""),
+          instructions: String(prev.assessment.params.instructions || ""),
+          input_schema: prev.assessment.params.input_schema,
           model: modelName,
           ...buildDefaultParams(modelName),
         },
@@ -330,38 +371,55 @@ export function usePromptAndConfigStep({
       toast.error("Please sign in to create configurations");
       return;
     }
-    if (!configName.trim()) {
+    const isVersion = saveMode === "version";
+    const targetConfig = isVersion
+      ? (configCards.find((c) => c.id === versionConfigId) ?? null)
+      : null;
+    if (isVersion) {
+      if (!targetConfig) {
+        toast.error("Select a configuration to version");
+        return;
+      }
+    } else if (!configName.trim()) {
       toast.error("Configuration name is required");
       return;
     }
     setIsSaving(true);
     try {
-      const existingConfig =
-        configCards.find(
-          (c) =>
-            c.name.trim().toLowerCase() === configName.trim().toLowerCase(),
-        ) ?? null;
+      const configBlob = buildAssessmentConfigBlob({
+        draft,
+        systemInstruction,
+        outputSchema,
+        columnMapping,
+        prefilterConfig,
+      });
       const saved = await saveAssessmentConfig({
         apiKey,
-        configName: configName.trim(),
+        configName: isVersion ? targetConfig!.name : configName.trim(),
         commitMessage: commitMessage.trim(),
-        configBlob: draft,
-        existingConfig: existingConfig
-          ? { id: existingConfig.id, name: existingConfig.name }
+        configBlob,
+        existingConfig: isVersion
+          ? { id: targetConfig!.id, name: targetConfig!.name }
           : null,
       });
       addSelection({
         config_id: saved.config_id,
         config_version: saved.config_version,
-        name: configName.trim(),
-        provider: draft.completion.provider,
+        name: saved.name ?? configName.trim(),
+        provider: draft.assessment.provider,
         model: currentModel,
       });
       setDraft(buildInitialAssessmentConfigDraft());
       setConfigName("");
       setCommitMessage("");
+      setVersionConfigId("");
+      setSaveMode("new");
       setConfigMode("existing");
-      toast.success("Configuration saved and added!");
+      toast.success(
+        isVersion
+          ? "New version saved and added!"
+          : "Configuration saved and added!",
+      );
       void loadConfigs(0, true);
     } catch (err) {
       toast.error(
@@ -404,11 +462,16 @@ export function usePromptAndConfigStep({
     configName,
     commitMessage,
     isSaving,
+    saveMode,
+    setSaveMode,
+    versionConfigId,
+    setVersionConfigId,
     setConfigName,
     setCommitMessage,
     handleProviderChange,
     handleModelChange,
     updateDraftParam,
     handleCreateAndAdd,
+    configBlob,
   };
 }
diff --git a/app/hooks/usePromptPlaceholderEditor.ts b/app/hooks/usePromptPlaceholderEditor.ts
index 2ffd69bc..7b5d5691 100644
--- a/app/hooks/usePromptPlaceholderEditor.ts
+++ b/app/hooks/usePromptPlaceholderEditor.ts
@@ -9,14 +9,13 @@ import {
   useRef,
   useState,
 } from "react";
-import type { SampleRow, ValueSetter } from "@/app/lib/types/assessment";
+import type { ValueSetter } from "@/app/lib/types/assessment";
 
 interface UsePromptPlaceholderEditorParams {
   value: string;
   onChange: ValueSetter<string>;
   previewMode: boolean;
   textColumns: string[];
-  sampleRow: SampleRow;
   enablePlaceholders: boolean;
 }
 
@@ -43,7 +42,6 @@ export function usePromptPlaceholderEditor({
   onChange,
   previewMode,
   textColumns,
-  sampleRow,
   enablePlaceholders,
 }: UsePromptPlaceholderEditorParams): UsePromptPlaceholderEditorResult {
   const [mentionQuery, setMentionQuery] = useState<string | null>(null);
@@ -257,20 +255,9 @@ export function usePromptPlaceholderEditor({
     return [...used, ...unused];
   }, [textColumns, usedColumns]);
 
-  const previewText = useMemo(() => {
-    if (!value.trim()) return "";
-    if (!enablePlaceholders) return value;
-
-    let next = value;
-    textColumns.forEach((col) => {
-      const safe = col.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
-      next = next.replace(
-        new RegExp(`\\{${safe}\\}`, "g"),
-        sampleRow[col] || "",
-      );
-    });
-    return next;
-  }, [enablePlaceholders, sampleRow, textColumns, value]);
+  // No dataset sample data in the dataset-independent flow, so the preview shows
+  // the composed prompt as written (placeholders remain visible).
+  const previewText = useMemo(() => (value.trim() ? value : ""), [value]);
 
   return {
     textareaRef,
diff --git a/app/lib/assessment/constants.ts b/app/lib/assessment/constants.ts
index a3bae083..86a9fb1a 100644
--- a/app/lib/assessment/constants.ts
+++ b/app/lib/assessment/constants.ts
@@ -1,5 +1,6 @@
 import type {
   AssessmentTab,
+  AssessmentTabId,
   ColumnRole,
   PostProcessingConfig,
   PostProcessingFilterRule,
@@ -91,11 +92,10 @@ export const SUMMARY_BADGE_CLASSES: Record<ResultTone, string> = {
 };
 
 export const ASSESSMENT_CONFIG_STEPS: Step[] = [
-  { id: 1, label: "Mapper" },
-  { id: 2, label: "Eliminatory (opt.)" },
-  { id: 3, label: "Evaluation" },
-  { id: 4, label: "Post Processing (opt.)" },
-  { id: 5, label: "Review" },
+  { id: 1, label: "Configuration" },
+  { id: 2, label: "Input Schema" },
+  { id: 3, label: "Pre-filter (opt.)" },
+  { id: 4, label: "Assessment" },
 ];
 
 export const SCHEMA_TYPE_OPTIONS: Array<{
@@ -250,11 +250,29 @@ export const CONFIGS_VISIBLE_BATCH_SIZE = 2;
 export const PAGE_TABS: ReadonlyArray<AssessmentTab> = [
   { id: "datasets", label: "Datasets" },
   { id: "config", label: "Config" },
-  { id: "results", label: "Result" },
+  { id: "experiment", label: "Experiment" },
+  { id: "results", label: "Runs" },
 ];
 
 export const MAX_CONFIGS = 4;
 
+// Each tab is its own route (sidebar sub-item). The `results` tab id keeps its
+// name for churn reasons but lives at the /assessment/runs URL.
+export const ASSESSMENT_TAB_ROUTES: Record<AssessmentTabId, string> = {
+  datasets: "/assessment",
+  config: "/assessment/config",
+  experiment: "/assessment/experiment",
+  results: "/assessment/runs",
+};
+
+// Reverse map from the /assessment/[tab] URL segment to the tab id.
+export const ASSESSMENT_ROUTE_SEGMENT_TO_TAB: Record<string, AssessmentTabId> =
+  {
+    config: "config",
+    experiment: "experiment",
+    runs: "results",
+  };
+
 export const ATTACHMENT_FORMATS: Record<string, string[]> = {
   mixed: ["url", "base64"],
   image: ["url", "base64"],
diff --git a/app/lib/assessment/results.ts b/app/lib/assessment/results.ts
index 91c1b808..90aacb34 100644
--- a/app/lib/assessment/results.ts
+++ b/app/lib/assessment/results.ts
@@ -67,16 +67,18 @@ export function hasViewableResults(run: AssessmentChildRun): boolean {
   return getStageProgress(run).some((s) => s.status === "completed");
 }
 
+// Backend status enums serialize UPPERCASE (e.g. "COMPLETED"); the status sets
+// are lowercase — compare case-insensitively so tones/badges resolve correctly.
 export function isActiveStatus(status: string): boolean {
-  return ACTIVE_ASSESSMENT_STATUSES.has(status);
+  return ACTIVE_ASSESSMENT_STATUSES.has(status.toLowerCase());
 }
 
 export function isFailedStatus(status: string): boolean {
-  return FAILED_ASSESSMENT_STATUSES.has(status);
+  return FAILED_ASSESSMENT_STATUSES.has(status.toLowerCase());
 }
 
 export function isCompletedStatus(status: string): boolean {
-  return COMPLETED_ASSESSMENT_STATUSES.has(status);
+  return COMPLETED_ASSESSMENT_STATUSES.has(status.toLowerCase());
 }
 
 export function canRetryStatus(status: string): boolean {
@@ -127,9 +129,10 @@ export function normalizeAssessmentRun(run: AssessmentRun): AssessmentRun {
 }
 
 export function getResultTone(status: string): ResultTone {
-  if (isCompletedStatus(status)) return "success";
-  if (status === "failed" || status === "prefilter_failed") return "error";
-  if (isActiveStatus(status) || status === "completed_with_errors") {
+  const s = status.toLowerCase();
+  if (isCompletedStatus(s)) return "success";
+  if (s === "failed" || s === "prefilter_failed") return "error";
+  if (isActiveStatus(s) || s === "completed_with_errors") {
     return "warning";
   }
   return "default";
@@ -162,7 +165,7 @@ export function filterAssessments(
   return assessments.filter((run) => {
     if (statusFilter === "processing") return isActiveStatus(run.status);
     if (statusFilter === "failed") return isFailedStatus(run.status);
-    return run.status === statusFilter;
+    return run.status.toLowerCase() === statusFilter;
   });
 }
 
diff --git a/app/lib/data/assessmentModels.ts b/app/lib/data/assessmentModels.ts
index f695ca04..b950f59b 100644
--- a/app/lib/data/assessmentModels.ts
+++ b/app/lib/data/assessmentModels.ts
@@ -3,7 +3,7 @@ import type {
   ConfigParamDefinition,
   ModelOption,
 } from "@/app/lib/types/assessment";
-import type { ConfigBlob } from "@/app/lib/types/configs";
+import type { AssessmentConfigBlob } from "@/app/lib/types/configs";
 
 export const GPT4_STYLE_CONFIG = {
   top_p: {
@@ -376,13 +376,14 @@ export function buildDefaultParams(
   );
 }
 
-export const ASSESSMENT_DEFAULT_CONFIG: ConfigBlob = {
-  completion: {
+export const ASSESSMENT_DEFAULT_CONFIG: AssessmentConfigBlob = {
+  assessment: {
     provider: "openai",
     type: "text",
     params: {
       model: "gpt-4o-mini",
       instructions: "",
+      input_schema: {},
       ...buildDefaultParams("gpt-4o-mini"),
     },
   },
diff --git a/app/lib/navConfig.ts b/app/lib/navConfig.ts
index 6ddad7d3..e0a87404 100644
--- a/app/lib/navConfig.ts
+++ b/app/lib/navConfig.ts
@@ -59,9 +59,14 @@ export const NAV_ITEMS: NavItemConfig[] = [
   },
   {
     name: "Assessment",
-    route: "/assessment",
     icon: "assessment",
     featureFlag: FeatureFlag.ASSESSMENT,
+    submenu: [
+      { name: "Datasets", route: "/assessment" },
+      { name: "Config", route: "/assessment/config" },
+      { name: "Experiment", route: "/assessment/experiment" },
+      { name: "Runs", route: "/assessment/runs" },
+    ],
     gateDescription: "Log in to run assessments.",
   },
   {
diff --git a/app/lib/store/assessment.ts b/app/lib/store/assessment.ts
index d29864be..bbb8da7c 100644
--- a/app/lib/store/assessment.ts
+++ b/app/lib/store/assessment.ts
@@ -1,46 +1,21 @@
-// Zustand store for the selected assessment dataset: id, columns, sample row, and column mapping.
+// Zustand store for the selected assessment dataset: id + name only. A dataset
+// is chosen in the Experiment tab to run a config against; the config itself is
+// authored dataset-independently, so no columns/mapping live here.
 import { create } from "zustand";
-import type {
-  AssessmentDatasetState,
-  ColumnMapping,
-} from "@/app/lib/types/assessment";
-
-const DEFAULT_MAPPING: ColumnMapping = {
-  textColumns: [],
-  attachments: [],
-  groundTruthColumns: [],
-};
+import type { AssessmentDatasetState } from "@/app/lib/types/assessment";
 
 export const useAssessmentDatasetStore = create<AssessmentDatasetState>()(
   (set) => ({
     datasetId: "",
     datasetName: "",
-    columns: [],
-    sampleRow: {},
-    columnMapping: DEFAULT_MAPPING,
 
     setDatasetId: (id) => set({ datasetId: id }),
     setDatasetName: (name) => set({ datasetName: name }),
 
-    setDataset: (datasetId, columns, sampleRow, datasetName) =>
-      set((state) => ({
-        datasetId,
-        datasetName: datasetName ?? state.datasetName,
-        columns,
-        sampleRow,
-        columnMapping:
-          datasetId !== state.datasetId ? DEFAULT_MAPPING : state.columnMapping,
-      })),
-
-    setColumnMapping: (mapping) => set({ columnMapping: mapping }),
-
     clearDataset: () =>
       set({
         datasetId: "",
         datasetName: "",
-        columns: [],
-        sampleRow: {},
-        columnMapping: DEFAULT_MAPPING,
       }),
   }),
 );
diff --git a/app/lib/types/assessment/config.ts b/app/lib/types/assessment/config.ts
index 72ecd8b5..2140e37d 100644
--- a/app/lib/types/assessment/config.ts
+++ b/app/lib/types/assessment/config.ts
@@ -1,5 +1,7 @@
 // Assessment types: model configurations, versions, and config-selection UI.
 import type {
+  AssessmentConfigBlob,
+  AssessmentInputSchemaColumn,
   CompletionConfig,
   ConfigPublic,
   ConfigVersionItems,
@@ -16,6 +18,14 @@ export interface ConfigSelection extends ConfigRef {
   name?: string;
   provider?: string;
   model?: string;
+  // Stored input_schema of the selected config version, used to build the run's
+  // input_binding without re-authoring a dataset mapping.
+  input_schema?: Record<string, AssessmentInputSchemaColumn>;
+}
+
+export interface AssessmentRunConfigRef {
+  id: string;
+  version: number;
 }
 
 export type ConfigParamType = "float" | "int" | "enum";
@@ -39,6 +49,9 @@ export type ModelOption = LabeledValue;
 
 export type ConfigMode = "existing" | "create";
 
+// Config-tab save modal: create a brand-new config vs. a new version of one.
+export type ConfigSaveMode = "new" | "version";
+
 export interface VersionListState {
   items: ConfigVersionItems[];
   isLoading: boolean;
@@ -83,6 +96,16 @@ export interface ConfigCreatorProps {
   configName: string;
   commitMessage: string;
   isSaving: boolean;
+  // Save modal open-state is lifted so the trigger button can live in the
+  // step-level footer while the modal renders here.
+  isSaveModalOpen: boolean;
+  setIsSaveModalOpen: ValueSetter<boolean>;
+  // Save modal: new config vs. new version of an existing config.
+  saveMode: ConfigSaveMode;
+  setSaveMode: ValueSetter<ConfigSaveMode>;
+  versionConfigId: string;
+  setVersionConfigId: ValueSetter<string>;
+  existingConfigs: ConfigPublic[];
   setConfigName: ValueSetter<string>;
   setCommitMessage: ValueSetter<string>;
   onProviderChange: ValueSetter<CompletionConfig["provider"]>;
@@ -126,39 +149,24 @@ export interface UsePromptAndConfigStepResult {
   configName: string;
   commitMessage: string;
   isSaving: boolean;
+  saveMode: ConfigSaveMode;
+  setSaveMode: ValueSetter<ConfigSaveMode>;
+  versionConfigId: string;
+  setVersionConfigId: ValueSetter<string>;
   setConfigName: ValueSetter<string>;
   setCommitMessage: ValueSetter<string>;
   handleProviderChange: (provider: CompletionConfig["provider"]) => void;
   handleModelChange: (modelName: string) => void;
   updateDraftParam: (key: string, value: string | number) => void;
   handleCreateAndAdd: () => Promise<void>;
+  configBlob: AssessmentConfigBlob;
 }
 
+// The Config tab renders only the "new configuration" builder (ConfigCreator);
+// selecting an existing saved config to run lives in the Experiment tab.
 export interface AssessmentConfigurationProps extends Omit<
   ConfigCreatorProps,
   "onSave"
 > {
-  configMode: ConfigMode;
-  setConfigMode: ValueSetter<ConfigMode>;
-  configs: ConfigSelection[];
-  onRemoveConfig: (configId: string, version: number) => void;
-  configCards: ConfigPublic[];
-  searchQuery: string;
-  setSearchQuery: ValueSetter<string>;
-  isLoadingConfigs: boolean;
-  hasMoreConfigs: boolean;
-  nextConfigSkip: number;
-  expandedConfigId: string | null;
-  versionStateByConfig: Record<string, VersionListState>;
-  latestModelByConfig: Record<string, LatestConfigModel>;
-  loadingSelectionKeys: Record<string, boolean>;
-  isSelected: (configId: string, version: number) => boolean;
-  onLoadMoreConfigs: (skip: number) => void | Promise<void>;
-  onLoadVersions: (configId: string, skip: number) => void;
-  onToggleConfigExpansion: ValueSetter<string>;
-  onToggleVersionSelection: (
-    config: ConfigPublic,
-    version: number,
-  ) => void | Promise<void>;
   onSaveConfig: () => void | Promise<void>;
 }
diff --git a/app/lib/types/assessment/core.ts b/app/lib/types/assessment/core.ts
index e4675fd6..c75f5889 100644
--- a/app/lib/types/assessment/core.ts
+++ b/app/lib/types/assessment/core.ts
@@ -21,7 +21,7 @@ export interface PagedResult<T> {
   nextSkip: number;
 }
 
-export type AssessmentTabId = "datasets" | "config" | "results";
+export type AssessmentTabId = "datasets" | "config" | "experiment" | "results";
 export interface AssessmentTab {
   id: AssessmentTabId;
   label: string;
diff --git a/app/lib/types/assessment/dataset.ts b/app/lib/types/assessment/dataset.ts
index ded47968..b26cab1e 100644
--- a/app/lib/types/assessment/dataset.ts
+++ b/app/lib/types/assessment/dataset.ts
@@ -4,7 +4,6 @@ import type {
   CreateResponse,
   LabeledValue,
   ListResponse,
-  SampleRow,
   StepNavigationProps,
   ValueSetter,
 } from "./core";
@@ -22,6 +21,9 @@ export interface ColumnMapping {
   textColumns: string[];
   attachments: Attachment[];
   groundTruthColumns: string[];
+  // Names of columns marked strict (required in every submission row). Any
+  // column not listed is optional (strict: false).
+  strictColumns?: string[];
 }
 
 export type ColumnRole = "unmapped" | "text" | "attachment" | "ground_truth";
@@ -65,6 +67,8 @@ export interface PrefilterStepProps extends StepNavigationProps {
   attachmentColumns?: string[];
   prefilterConfig: PrefilterConfig | null;
   setPrefilterConfig: ValueSetter<PrefilterConfig | null>;
+  // Changes when a config is (re)loaded, so local state re-syncs from props.
+  syncToken?: number;
 }
 
 export interface ColumnConfig {
@@ -83,27 +87,21 @@ export interface RoleVisuals {
   activeButtonClass: string;
 }
 
-export interface ColumnMapperStepProps extends StepNavigationProps {
-  columns: string[];
+// The Mapper authors the config's input_schema directly as a manual field list;
+// it no longer maps a dataset's columns, so it takes no `columns` and no back nav.
+export interface ColumnMapperStepProps {
   columnMapping: ColumnMapping;
   setColumnMapping: ValueSetter<ColumnMapping>;
+  onNext: () => void;
+  // Changes when a config is (re)loaded, so the local field list re-syncs.
+  syncToken?: number;
 }
 
 export interface AssessmentDatasetState {
   datasetId: string;
   datasetName: string;
-  columns: string[];
-  sampleRow: SampleRow;
-  columnMapping: ColumnMapping;
   setDatasetId: ValueSetter<string>;
   setDatasetName: ValueSetter<string>;
-  setDataset: (
-    datasetId: string,
-    columns: string[],
-    sampleRow: SampleRow,
-    datasetName?: string,
-  ) => void;
-  setColumnMapping: ValueSetter<ColumnMapping>;
   clearDataset: () => void;
 }
 
@@ -144,6 +142,13 @@ export interface DatasetViewModalData {
   rows: string[][];
 }
 
+// GET /api/assessment/datasets/{id}/rows — all rows, column-keyed.
+export interface AssessmentDatasetRows {
+  headers: string[];
+  rows: Record<string, string>[];
+  total_rows: number;
+}
+
 export type ReviewColumnRole = "text" | "attachment" | "ground truth";
 
 export interface ReviewColumn {
diff --git a/app/lib/types/assessment/results.ts b/app/lib/types/assessment/results.ts
index 13f1cc9d..2e9a4aea 100644
--- a/app/lib/types/assessment/results.ts
+++ b/app/lib/types/assessment/results.ts
@@ -26,6 +26,19 @@ export interface AssessmentRunStat {
   stage_status: string | null;
 }
 
+export interface AssessmentPreFilterCost {
+  topic_relevance?: number | null;
+  duplicate_detection?: number | null;
+  total: number;
+}
+
+export interface AssessmentCost {
+  pre_filter: AssessmentPreFilterCost;
+  assessment: number;
+  total: number;
+  currency: string;
+}
+
 export interface AssessmentRun {
   id: number;
   experiment_name: string;
@@ -37,6 +50,7 @@ export interface AssessmentRun {
   processing_runs: number;
   completed_runs: number;
   failed_runs: number;
+  counts?: ResultsCounts | null;
   run_stats: AssessmentRunStat[];
   error_message: string | null;
   inserted_at: string;
@@ -79,11 +93,14 @@ export interface AssessmentChildRun {
   id: number;
   assessment_id: number | null;
   run_name: string;
+  experiment_name?: string | null;
   dataset_name: string | null;
   dataset_id: number | null;
   config_id: string | null;
   config_version: number | null;
   status: string;
+  input?: Record<string, unknown> | null;
+  cost?: AssessmentCost | null;
   total_items: number;
   error_message: string | null;
   organization_id: number;
diff --git a/app/lib/types/assessment/workflow.ts b/app/lib/types/assessment/workflow.ts
index 64e2293b..e4a41111 100644
--- a/app/lib/types/assessment/workflow.ts
+++ b/app/lib/types/assessment/workflow.ts
@@ -8,9 +8,37 @@ import type {
   ValueSetter,
   WithForbiddenHandler,
 } from "./core";
-import type { ConfigSelection } from "./config";
+import type { ConfigSelection, ConfigSaveMode } from "./config";
 import type { ColumnMapping, PrefilterConfig, SchemaProperty } from "./dataset";
 import type { PostProcessingConfig } from "./results";
+import type { AssessmentConfigBlob } from "@/app/lib/types/configs";
+
+// One-shot seed passed from the Configuration step to the Assessment step so a
+// loaded config version hydrates the provider/model draft + save mode. `nonce`
+// changes on every (re)load so the effect that applies it fires once per load.
+export interface ConfigDraftSeed {
+  blob: AssessmentConfigBlob | null;
+  saveMode: ConfigSaveMode;
+  configId: string;
+  configName: string;
+  nonce: number;
+}
+
+// Config flow step 1: start a new configuration or load an existing one (and a
+// specific version) to edit into a new version.
+export interface ConfigSelectStepProps {
+  onStartNew: () => void;
+  onLoadExisting: (
+    blob: AssessmentConfigBlob,
+    configId: string,
+    configName: string,
+  ) => void;
+  onForbidden: () => void;
+  onNext: () => void;
+  // Which config scope to list/load. ASSESSMENT when rendered from the
+  // assessment flow; default when reused from the configuration library.
+  tag?: "default" | "ASSESSMENT";
+}
 
 export interface AssessmentFormState {
   experimentName: string;
@@ -28,12 +56,8 @@ export interface AssessmentFormState {
 }
 
 export interface PromptPanelProps {
-  textColumns: string[];
-  sampleRow: SampleRow;
   systemInstruction: string;
   setSystemInstruction: ValueSetter<string>;
-  promptTemplate: string;
-  setPromptTemplate: ValueSetter<string>;
 }
 
 export interface ResponseSchemaProps {
@@ -43,47 +67,70 @@ export interface ResponseSchemaProps {
   hasFields: boolean;
 }
 
+// Config tab authors + saves a dataset-independent config (Mapper builds the
+// input_schema directly -> Eliminatory -> Evaluation). Run submission lives in
+// the Experiment tab, so no dataset/submit/postprocessing here.
 export interface ConfigPanelProps {
-  canSubmitAssessment: boolean;
-  columns: string[];
   columnMapping: ColumnMapping;
   completedSteps: Set<number>;
   configStep: number;
   configs: ConfigSelection[];
-  datasetId: string | null;
-  experimentName: string;
-  formState: AssessmentFormState;
-  hasDataset: boolean;
-  isSubmitting: boolean;
   prefilterConfig: PrefilterConfig | null;
   outputSchema: SchemaProperty[];
   systemInstruction: string;
   promptTemplate: string;
-  sampleRow: SampleRow;
-  setActiveTabToDatasets: () => void;
   setColumnMapping: ValueSetter<ColumnMapping>;
   setConfigStep: ValueSetter<number>;
   setConfigs: StateSetter<ConfigSelection[]>;
-  setExperimentName: ValueSetter<string>;
   setPrefilterConfig: ValueSetter<PrefilterConfig | null>;
   setOutputSchema: ValueSetter<SchemaProperty[]>;
   setSystemInstruction: ValueSetter<string>;
   setPromptTemplate: ValueSetter<string>;
-  postProcessingConfig: PostProcessingConfig | null;
-  setPostProcessingConfig: ValueSetter<PostProcessingConfig | null>;
+  onStepComplete: ValueSetter<number>;
+  configSeed: ConfigDraftSeed | null;
+  onStartNewConfig: () => void;
+  onLoadExistingConfig: (
+    blob: AssessmentConfigBlob,
+    configId: string,
+    configName: string,
+  ) => void;
+  onForbidden: () => void;
+}
+
+// Experiment tab: pick a saved config + a dataset, then dispatch a run.
+export interface ExperimentTabProps extends WithForbiddenHandler {
+  // Saved-config picker (fed to usePromptAndConfigStep).
+  textColumns: string[];
+  promptTemplate: string;
+  setPromptTemplate: ValueSetter<string>;
+  configs: ConfigSelection[];
+  setConfigs: StateSetter<ConfigSelection[]>;
+  outputSchema: SchemaProperty[];
+  systemInstruction: string;
+  columnMapping: ColumnMapping;
+  prefilterConfig: PrefilterConfig | null;
+  // Dataset picker (fed to useAssessmentDatasetsTab).
+  datasetId: string;
+  datasetName: string;
+  setDatasetId: ValueSetter<string>;
+  setSelectedDatasetName: ValueSetter<string>;
+  // Run dispatch.
+  experimentName: string;
+  setExperimentName: ValueSetter<string>;
+  isSubmitting: boolean;
+  canSubmit: boolean;
   submitBlockerMessage: string;
   onSubmit: () => void;
-  onStepComplete: ValueSetter<number>;
 }
 
 export type EvaluationsTabProps = WithForbiddenHandler;
 
+// The Datasets tab manages the dataset library (list / view / create / delete).
+// Dataset selection for a run happens in the Experiment tab, not here.
 export interface DatasetsTabProps extends WithForbiddenHandler {
   datasetId: string;
   setDatasetId: ValueSetter<string>;
   setSelectedDatasetName: ValueSetter<string>;
-  onColumnsLoaded: (columns: string[], sampleRow?: SampleRow) => void;
-  onNext: () => void;
 }
 
 export interface PageLayoutProps {
@@ -92,6 +139,7 @@ export interface PageLayoutProps {
   onTabSwitch: ValueSetter<AssessmentTabId>;
   datasetsTabProps: DatasetsTabProps;
   configPanelProps: ConfigPanelProps;
+  experimentTabProps: ExperimentTabProps;
   evaluationsTabProps: EvaluationsTabProps;
 }
 
@@ -111,7 +159,6 @@ export interface PostProcessingPanelProps {
 
 export interface PromptAndConfigStepProps extends StepNavigationProps {
   textColumns: string[];
-  sampleRow: SampleRow;
   systemInstruction: string;
   setSystemInstruction: ValueSetter<string>;
   promptTemplate: string;
@@ -120,4 +167,7 @@ export interface PromptAndConfigStepProps extends StepNavigationProps {
   setConfigs: StateSetter<ConfigSelection[]>;
   outputSchema: SchemaProperty[];
   setOutputSchema: ValueSetter<SchemaProperty[]>;
+  columnMapping: ColumnMapping;
+  prefilterConfig: PrefilterConfig | null;
+  configSeed?: ConfigDraftSeed | null;
 }
diff --git a/app/lib/types/configs.ts b/app/lib/types/configs.ts
index 1ab8a890..e08368cf 100644
--- a/app/lib/types/configs.ts
+++ b/app/lib/types/configs.ts
@@ -90,10 +90,56 @@ export interface ConfigBlob {
   output_guardrails?: GuardrailRef[];
 }
 
+export type AssessmentColumnType = "text" | "image" | "pdf";
+
+export interface AssessmentInputSchemaColumn {
+  type: AssessmentColumnType;
+  format?: "url";
+  // Whether the column must be present in every submission row (default false).
+  strict?: boolean;
+}
+
+export interface AssessmentParams {
+  model: string;
+  instructions: string;
+  input_schema: Record<string, AssessmentInputSchemaColumn>;
+  json_output_schema?: object | null;
+  [key: string]: unknown;
+}
+
+export interface AssessmentModelBlock {
+  provider: ProviderType;
+  type: "text";
+  params: AssessmentParams;
+}
+
+export interface AssessmentPreFilterParams {
+  model?: string;
+  instructions: string;
+  [key: string]: unknown;
+}
+
+export interface AssessmentPreFilter {
+  provider: ProviderType;
+  params: AssessmentPreFilterParams;
+  stop_on_fail: boolean;
+  knowledge_base_id?: string;
+}
+
+export interface AssessmentPreFilters {
+  topic_relevance?: AssessmentPreFilter;
+  duplicate_detection?: AssessmentPreFilter;
+}
+
+export interface AssessmentConfigBlob {
+  pre_filters?: AssessmentPreFilters;
+  assessment: AssessmentModelBlock;
+}
+
 export interface ConfigCreate {
   name: string;
   description?: string | null;
-  config_blob: ConfigBlob;
+  config_blob: ConfigBlob | AssessmentConfigBlob;
   commit_message?: string | null;
   tag?: ConfigTag | null;
 }
@@ -105,7 +151,7 @@ export interface ConfigUpdate {
 }
 
 export interface ConfigVersionCreate {
-  config_blob: ConfigBlob;
+  config_blob: ConfigBlob | AssessmentConfigBlob;
   commit_message?: string | null;
 }
 
diff --git a/app/lib/utils/assessment.ts b/app/lib/utils/assessment.ts
index 383dbb4a..40b3d11d 100644
--- a/app/lib/utils/assessment.ts
+++ b/app/lib/utils/assessment.ts
@@ -239,45 +239,40 @@ export function isBlankCell(cell: string | undefined): boolean {
   return cell == null || String(cell).trim() === "";
 }
 
+// A run pairs a saved config with a dataset. The config already carries its
+// input_schema + output schema, so the run only validates dataset, config
+// selection, that the chosen config defines input fields, and a run name.
 interface AssessmentSubmitChecks {
   datasetId: string | null;
-  hasMapperSelection: boolean;
-  hasResponseFormat: boolean;
+  hasInputSchema: boolean;
   configCount: number;
   experimentName: string;
+  hasPrompt: boolean;
 }
 
 export function getAssessmentSubmitError(
   checks: AssessmentSubmitChecks,
 ): string | null {
   if (!checks.datasetId) return "Dataset is required";
-  if (!checks.hasMapperSelection)
-    return "Map at least one text or attachment column";
-  if (!checks.hasResponseFormat) return "Response format is required";
   if (checks.configCount === 0) return "Select at least one configuration";
+  if (!checks.hasInputSchema)
+    return "Selected configuration has no input fields";
   if (!checks.experimentName.trim()) return "Experiment name is required";
+  if (!checks.hasPrompt) return "Enter a user prompt";
   return null;
 }
 
-interface AssessmentSubmitBlockerChecks {
-  datasetId: string | null;
-  hasMapperSelection: boolean;
-  hasResponseFormat: boolean;
-  configCount: number;
-  experimentName: string;
-}
-
 export function getAssessmentSubmitBlocker(
-  checks: AssessmentSubmitBlockerChecks,
+  checks: AssessmentSubmitChecks,
 ): string {
   if (!checks.datasetId) return "Select a dataset to submit";
-  if (!checks.hasMapperSelection)
-    return "Map at least one text or attachment column to submit";
-  if (!checks.hasResponseFormat) return "Set response format to submit";
   if (checks.configCount === 0)
     return "Select at least one configuration to submit";
+  if (!checks.hasInputSchema)
+    return "Selected configuration has no input fields";
   if (!checks.experimentName.trim())
     return "Enter an experiment name to submit";
+  if (!checks.hasPrompt) return "Enter a user prompt to submit";
   return "";
 }
 
diff --git a/app/lib/utils/assessmentFetcher.ts b/app/lib/utils/assessmentFetcher.ts
index 46635e72..e8110224 100644
--- a/app/lib/utils/assessmentFetcher.ts
+++ b/app/lib/utils/assessmentFetcher.ts
@@ -8,16 +8,25 @@ import {
   GPT4_STYLE_CONFIG,
 } from "@/app/lib/data/assessmentModels";
 import { DEFAULT_PAGE_LIMIT } from "@/app/lib/constants";
+import { schemaToJsonSchema } from "@/app/lib/utils/assessment";
+import { fromJsonSchema } from "@/app/lib/utils/outputSchema";
 import type {
+  AssessmentDatasetRows,
+  Attachment,
+  ColumnMapping,
   ConfigParamDefinition,
   ConfigSelection,
   ModelOption,
   PagedResult,
+  PrefilterConfig,
+  SchemaProperty,
   VersionListState,
 } from "@/app/lib/types/assessment";
 import type {
-  CompletionParams,
-  ConfigBlob,
+  AssessmentConfigBlob,
+  AssessmentInputSchemaColumn,
+  AssessmentParams,
+  AssessmentPreFilters,
   ConfigCreate,
   ConfigListResponse,
   ConfigPublic,
@@ -27,6 +36,7 @@ import type {
   ConfigVersionPublic,
   ConfigVersionResponse,
   ConfigWithVersionResponse,
+  ProviderType,
   SavedConfig,
 } from "@/app/lib/types/configs";
 
@@ -61,8 +71,10 @@ export function buildDefaultParams(
   );
 }
 
-export function buildInitialAssessmentConfigDraft(): ConfigBlob {
-  return JSON.parse(JSON.stringify(ASSESSMENT_DEFAULT_CONFIG)) as ConfigBlob;
+export function buildInitialAssessmentConfigDraft(): AssessmentConfigBlob {
+  return JSON.parse(
+    JSON.stringify(ASSESSMENT_DEFAULT_CONFIG),
+  ) as AssessmentConfigBlob;
 }
 
 export function buildInitialAssessmentVersionState(): VersionListState {
@@ -97,33 +109,254 @@ function buildPageResult<T>(
   };
 }
 
-function normalizeConfigBlobForApi(configBlob: ConfigBlob): ConfigBlob {
-  const nextParams: Partial<CompletionParams> = {};
-  Object.entries(configBlob.completion.params).forEach(([key, value]) => {
+const PRESERVED_ASSESSMENT_PARAM_KEYS = new Set([
+  "model",
+  "instructions",
+  "input_schema",
+  "json_output_schema",
+]);
+
+// Assessment config_blob provider must be a backend TextProvider
+// (openai | google | anthropic). The model catalog uses "google-aistudio" for
+// Gemini (the credential provider), so narrow it to "google" at the API boundary.
+function toTextProvider(provider: ProviderType): ProviderType {
+  return (provider === "google-aistudio" ? "google" : provider) as ProviderType;
+}
+
+function normalizeConfigBlobForApi(
+  configBlob: AssessmentConfigBlob,
+): AssessmentConfigBlob {
+  const src = configBlob.assessment.params;
+  const nextParams: AssessmentParams = {
+    model: src.model,
+    instructions: src.instructions,
+    input_schema: src.input_schema,
+  };
+  if (src.json_output_schema != null) {
+    nextParams.json_output_schema = src.json_output_schema;
+  }
+  Object.entries(src).forEach(([key, value]) => {
+    if (PRESERVED_ASSESSMENT_PARAM_KEYS.has(key)) return;
     if (value !== undefined && value !== "") {
       nextParams[key] = value;
     }
   });
-  return {
-    completion: {
-      provider: configBlob.completion.provider,
+
+  const normalized: AssessmentConfigBlob = {
+    assessment: {
+      provider: toTextProvider(configBlob.assessment.provider),
       type: "text",
-      params: nextParams as CompletionParams,
+      params: nextParams,
     },
   };
+  if (
+    configBlob.pre_filters &&
+    Object.keys(configBlob.pre_filters).length > 0
+  ) {
+    const preFilters = { ...configBlob.pre_filters };
+    if (preFilters.topic_relevance) {
+      preFilters.topic_relevance = {
+        ...preFilters.topic_relevance,
+        provider: toTextProvider(preFilters.topic_relevance.provider),
+      };
+    }
+    if (preFilters.duplicate_detection) {
+      preFilters.duplicate_detection = {
+        ...preFilters.duplicate_detection,
+        provider: toTextProvider(preFilters.duplicate_detection.provider),
+      };
+    }
+    normalized.pre_filters = preFilters;
+  }
+  return normalized;
+}
+
+export function buildAssessmentInputSchema(
+  columnMapping: ColumnMapping,
+): Record<string, AssessmentInputSchemaColumn> {
+  const strictColumns = new Set(columnMapping.strictColumns ?? []);
+  const schema: Record<string, AssessmentInputSchemaColumn> = {};
+  for (const column of columnMapping.textColumns) {
+    schema[column] = { type: "text", strict: strictColumns.has(column) };
+  }
+  for (const attachment of columnMapping.attachments) {
+    const type = attachment.type === "pdf" ? "pdf" : "image";
+    schema[attachment.column] = {
+      type,
+      format: "url",
+      strict: strictColumns.has(attachment.column),
+    };
+  }
+  return schema;
+}
+
+function buildPreFilters(
+  prefilterConfig: PrefilterConfig | null,
+  provider: ProviderType,
+  model: string,
+): AssessmentPreFilters | undefined {
+  if (!prefilterConfig) return undefined;
+  const preFilters: AssessmentPreFilters = {};
+  if (prefilterConfig.topic_relevance?.prompt?.trim()) {
+    preFilters.topic_relevance = {
+      provider,
+      params: {
+        model,
+        instructions: prefilterConfig.topic_relevance.prompt.trim(),
+      },
+      stop_on_fail: true,
+    };
+  }
+  if (prefilterConfig.duplicate_detection) {
+    preFilters.duplicate_detection = {
+      provider,
+      params: {
+        model,
+        instructions: "Flag rows that duplicate an earlier row.",
+      },
+      stop_on_fail: false,
+    };
+  }
+  return Object.keys(preFilters).length > 0 ? preFilters : undefined;
+}
+
+export function buildAssessmentConfigBlob(params: {
+  draft: AssessmentConfigBlob;
+  systemInstruction: string;
+  outputSchema: SchemaProperty[];
+  columnMapping: ColumnMapping;
+  prefilterConfig: PrefilterConfig | null;
+}): AssessmentConfigBlob {
+  const { draft, systemInstruction, outputSchema, columnMapping } = params;
+  const provider = draft.assessment.provider;
+  const model = String(draft.assessment.params.model || "");
+  const jsonOutputSchema = schemaToJsonSchema(outputSchema);
+
+  const nextParams: AssessmentParams = {
+    ...draft.assessment.params,
+    model,
+    instructions: systemInstruction.trim(),
+    input_schema: buildAssessmentInputSchema(columnMapping),
+  };
+  if (jsonOutputSchema) {
+    nextParams.json_output_schema = jsonOutputSchema;
+  } else {
+    delete nextParams.json_output_schema;
+  }
+
+  const blob: AssessmentConfigBlob = {
+    assessment: { provider, type: "text", params: nextParams },
+  };
+  const preFilters = buildPreFilters(params.prefilterConfig, provider, model);
+  if (preFilters) blob.pre_filters = preFilters;
+  return blob;
+}
+
+export interface AssessmentBuilderState {
+  draft: AssessmentConfigBlob;
+  systemInstruction: string;
+  outputSchema: SchemaProperty[];
+  columnMapping: ColumnMapping;
+  prefilterConfig: PrefilterConfig | null;
+}
+
+// Inverse of buildAssessmentConfigBlob: hydrate the builder from a saved
+// config version's blob so an existing config can be loaded and edited into a
+// new version. Pre-filter column selections are not stored in the blob, so
+// they come back empty (the criteria/prompt is preserved).
+export function assessmentBlobToBuilderState(
+  blob: AssessmentConfigBlob,
+): AssessmentBuilderState {
+  if (!blob?.assessment?.params) {
+    throw new Error(
+      "This configuration is not a valid assessment config (no assessment block).",
+    );
+  }
+  const params = blob.assessment.params as Record<string, unknown>;
+  const inputSchema = (params.input_schema ?? {}) as Record<
+    string,
+    AssessmentInputSchemaColumn
+  >;
+
+  const textColumns: string[] = [];
+  const attachments: Attachment[] = [];
+  const strictColumns: string[] = [];
+  for (const [name, column] of Object.entries(inputSchema)) {
+    if (column.type === "text") {
+      textColumns.push(name);
+    } else {
+      attachments.push({
+        column: name,
+        type: column.type,
+        format: column.format ?? "url",
+      });
+    }
+    if (column.strict) strictColumns.push(name);
+  }
+
+  const jsonOutputSchema = params.json_output_schema as
+    | Record<string, unknown>
+    | undefined;
+
+  let prefilterConfig: PrefilterConfig | null = null;
+  if (blob.pre_filters) {
+    prefilterConfig = {};
+    const tr = blob.pre_filters.topic_relevance;
+    if (tr) {
+      const trParams = (tr.params ?? {}) as Record<string, unknown>;
+      prefilterConfig.topic_relevance = {
+        columns: [],
+        prompt: String(trParams.instructions ?? ""),
+      };
+    }
+    if (blob.pre_filters.duplicate_detection) {
+      prefilterConfig.duplicate_detection = { columns: [] };
+    }
+  }
+
+  return {
+    draft: blob,
+    systemInstruction: String(params.instructions ?? ""),
+    outputSchema: jsonOutputSchema ? fromJsonSchema(jsonOutputSchema) : [],
+    columnMapping: {
+      textColumns,
+      attachments,
+      groundTruthColumns: [],
+      strictColumns,
+    },
+    prefilterConfig,
+  };
+}
+
+export async function fetchAssessmentDatasetRows(
+  datasetId: string,
+  apiKey: string,
+): Promise<AssessmentDatasetRows> {
+  // Endpoint returns APIResponse[AssessmentDatasetRows] — unwrap the envelope
+  // so callers get { headers, rows, total_rows } directly.
+  const res = await apiFetch<{
+    success: boolean;
+    data: AssessmentDatasetRows | null;
+    error?: string;
+  }>(`/api/assessment/datasets/${datasetId}/rows`, apiKey);
+  if (!res.success || !res.data) {
+    throw new Error(res.error || "Failed to fetch dataset rows");
+  }
+  return res.data;
 }
 
 export async function fetchConfigPage(params: {
   apiKey: string;
   skip?: number;
   limit?: number;
+  tag?: string;
 }): Promise<PagedResult<ConfigPublic>> {
   const skip = params.skip ?? 0;
   const limit = params.limit ?? DEFAULT_PAGE_LIMIT;
   const query = new URLSearchParams({
     skip: String(skip),
     limit: String(limit),
-    tag: ASSESSMENT_TAG,
+    tag: params.tag ?? ASSESSMENT_TAG,
   });
   const data = await apiFetch<ConfigListResponse>(
     `/api/configs?${query.toString()}`,
@@ -138,14 +371,14 @@ export async function fetchConfigPage(params: {
 export async function fetchConfigVersionsPage(
   apiKey: string,
   configId: string,
-  params: { skip?: number; limit?: number },
+  params: { skip?: number; limit?: number; tag?: string },
 ): Promise<PagedResult<ConfigVersionItems>> {
   const skip = params.skip ?? 0;
   const limit = params.limit ?? DEFAULT_PAGE_LIMIT;
   const query = new URLSearchParams({
     skip: String(skip),
     limit: String(limit),
-    tag: ASSESSMENT_TAG,
+    tag: params.tag ?? ASSESSMENT_TAG,
   });
   const data = await apiFetch<ConfigVersionListResponse>(
     `/api/configs/${configId}/versions?${query.toString()}`,
@@ -161,8 +394,9 @@ export async function fetchConfigVersionDetail(
   apiKey: string,
   configId: string,
   versionNumber: number,
+  tag: string = ASSESSMENT_TAG,
 ): Promise<ConfigVersionPublic> {
-  const query = new URLSearchParams({ tag: ASSESSMENT_TAG });
+  const query = new URLSearchParams({ tag });
   const data = await apiFetch<ConfigVersionResponse>(
     `/api/configs/${configId}/versions/${versionNumber}?${query.toString()}`,
     apiKey,
@@ -183,13 +417,15 @@ export async function fetchConfigSelection(
     config.id,
     versionNumber,
   );
-  const completion = version.config_blob.completion;
+  const blob = version.config_blob as unknown as AssessmentConfigBlob;
+  const assessment = blob.assessment;
   return {
     config_id: config.id,
     config_version: version.version,
     name: config.name,
-    provider: completion.provider,
-    model: String(completion.params.model || ""),
+    provider: assessment?.provider ?? "",
+    model: String(assessment?.params?.model || ""),
+    input_schema: assessment?.params?.input_schema ?? {},
   };
 }
 
@@ -197,23 +433,19 @@ export async function saveAssessmentConfig(params: {
   apiKey: string;
   configName: string;
   commitMessage: string;
-  configBlob: ConfigBlob;
+  configBlob: AssessmentConfigBlob;
   existingConfig: { id: string; name: string } | null;
 }): Promise<ConfigSelection> {
   const { apiKey, existingConfig } = params;
 
-  if (!apiKey) {
-    throw new Error("No API key selected. Please choose one in the Keystore.");
-  }
-
   const trimmedName = params.configName.trim();
   if (!trimmedName) {
     throw new Error("Configuration name is required");
   }
 
   const normalizedBlob = normalizeConfigBlobForApi(params.configBlob);
-  const provider = normalizedBlob.completion.provider;
-  const model = String(normalizedBlob.completion.params.model || "");
+  const provider = normalizedBlob.assessment.provider;
+  const model = String(normalizedBlob.assessment.params.model || "");
 
   if (existingConfig) {
     const versionCreate: ConfigVersionCreate = {