diff --git a/workbench/_web/src/app/workbench/[workspaceId]/patch-lens/[chartId]/components/PatchLensArea.tsx b/workbench/_web/src/app/workbench/[workspaceId]/patch-lens/[chartId]/components/PatchLensArea.tsx
index 280c5a35..5b1a4590 100644
--- a/workbench/_web/src/app/workbench/[workspaceId]/patch-lens/[chartId]/components/PatchLensArea.tsx
+++ b/workbench/_web/src/app/workbench/[workspaceId]/patch-lens/[chartId]/components/PatchLensArea.tsx
@@ -23,6 +23,9 @@ import { TutorialActivityPanel } from "./tutorial/TutorialActivityPanel";
 import { getModels } from "@/lib/api/modelsApi";
 import { useWorkspaceWorkshop } from "@/lib/api/workshopApi";
 import { useWorkspaceTutorial } from "@/lib/api/tutorialContentApi";
+import { getWorkspaceById } from "@/lib/queries/workspaceQueries";
+import { withProlificPid } from "@/lib/prolific";
+import { queryKeys } from "@/lib/queryKeys";
 import { useWorkspace } from "@/stores/useWorkspace";
 import { encodeText } from "@/actions/tok";
 import { TokenizerLoadError } from "@/actions/errors";
@@ -167,6 +170,17 @@ export default function PatchLensArea({
         workspaceId as string,
     );
 
+    // The workspace's captured Prolific identifiers (set on first arrival via the
+    // /w join link) — used to pass PROLIFIC_PID through to the post-survey so the
+    // response can be matched back to the study. Same cache key as elsewhere, so
+    // this is usually a hit rather than a fresh fetch.
+    const { data: workspace } = useQuery({
+        queryKey: queryKeys.workspaces.workspace(workspaceId as string),
+        queryFn: () => getWorkspaceById(workspaceId as string),
+        enabled: !!workspaceId,
+    });
+    const surveyUrl = withProlificPid(workshop?.surveyUrl, workspace?.prolific?.prolificPid);
+
     // Default to Llama-3.1-8B once when models load, rather than leaving the
     // workspace default at index 0 (the 70B, 80 layers). Guarded so a later
     // manual model choice is not overridden. Waits for the workshop lookup so
@@ -715,7 +729,7 @@ export default function PatchLensArea({
                     topToken={runTokens.top}
                     secondToken={runTokens.second}
                     runUnitIdx={runTokens.unitIdx}
-                    surveyUrl={workshop?.surveyUrl}
+                    surveyUrl={surveyUrl}
                     completionThanks={workshop?.completionText}
                     workshopMode={!!workshop}
                     onSpotlight={setSpotlight}
diff --git a/workbench/_web/src/lib/__tests__/prolific.test.ts b/workbench/_web/src/lib/__tests__/prolific.test.ts
new file mode 100644
index 00000000..4562a1de
--- /dev/null
+++ b/workbench/_web/src/lib/__tests__/prolific.test.ts
@@ -0,0 +1,69 @@
+/**
+ * Unit tests for Prolific param parsing + survey-URL pass-through.
+ */
+
+import { describe, it, expect } from "bun:test";
+import { parseProlificParams, withProlificPid } from "@/lib/prolific";
+
+describe("parseProlificParams", () => {
+    it("reads canonical UPPER_CASE keys", () => {
+        expect(
+            parseProlificParams({ PROLIFIC_PID: "p1", STUDY_ID: "s1", SESSION_ID: "x1" }),
+        ).toEqual({ prolificPid: "p1", studyId: "s1", sessionId: "x1" });
+    });
+
+    it("accepts lower_case defensively and trims", () => {
+        expect(parseProlificParams({ prolific_pid: "  p1  " })).toEqual({ prolificPid: "p1" });
+    });
+
+    it("collapses repeated params to the first value", () => {
+        expect(parseProlificParams({ PROLIFIC_PID: ["p1", "p2"] })).toEqual({ prolificPid: "p1" });
+    });
+
+    it("returns null when nothing is present (store nothing, not {})", () => {
+        expect(parseProlificParams({})).toBeNull();
+        expect(parseProlificParams({ PROLIFIC_PID: "  " })).toBeNull();
+    });
+});
+
+describe("withProlificPid", () => {
+    it("appends PROLIFIC_PID to a bare survey URL", () => {
+        expect(withProlificPid("https://survey.qualtrics.com/jfe/form/SV_x", "p1")).toBe(
+            "https://survey.qualtrics.com/jfe/form/SV_x?PROLIFIC_PID=p1",
+        );
+    });
+
+    it("merges with an existing query string rather than clobbering it", () => {
+        expect(withProlificPid("https://survey.example.com/s?foo=bar", "p1")).toBe(
+            "https://survey.example.com/s?foo=bar&PROLIFIC_PID=p1",
+        );
+    });
+
+    it("overwrites a stale PROLIFIC_PID instead of duplicating it", () => {
+        expect(withProlificPid("https://survey.example.com/s?PROLIFIC_PID=old", "new")).toBe(
+            "https://survey.example.com/s?PROLIFIC_PID=new",
+        );
+    });
+
+    it("URL-encodes the pid value", () => {
+        expect(withProlificPid("https://survey.example.com/s", "a b&c")).toBe(
+            "https://survey.example.com/s?PROLIFIC_PID=a+b%26c",
+        );
+    });
+
+    it("passes the URL through untouched when no pid is set", () => {
+        const url = "https://survey.example.com/s";
+        expect(withProlificPid(url, undefined)).toBe(url);
+        expect(withProlificPid(url, "")).toBe(url);
+    });
+
+    it("passes through when there is no survey URL", () => {
+        expect(withProlificPid(undefined, "p1")).toBeUndefined();
+        expect(withProlificPid("", "p1")).toBe("");
+    });
+
+    it("returns a non-absolute/malformed URL unchanged", () => {
+        expect(withProlificPid("/relative/survey", "p1")).toBe("/relative/survey");
+        expect(withProlificPid("not a url", "p1")).toBe("not a url");
+    });
+});
diff --git a/workbench/_web/src/lib/prolific.ts b/workbench/_web/src/lib/prolific.ts
index 4a2c961c..9794b1f7 100644
--- a/workbench/_web/src/lib/prolific.ts
+++ b/workbench/_web/src/lib/prolific.ts
@@ -39,3 +39,26 @@ export function parseProlificParams(searchParams: RawSearchParams): ProlificPara
 
     return Object.keys(params).length > 0 ? params : null;
 }
+
+/**
+ * Appends the participant's Prolific PID to a survey URL so the post-survey
+ * (Qualtrics) can tie the response back to the study — the final link becomes
+ * `…?PROLIFIC_PID=<pid>` (merged with any existing query string). Prolific and
+ * Qualtrics expect the literal UPPER_CASE key. Returns the URL untouched when
+ * there's no PID (participant didn't arrive via Prolific), no URL, or the URL
+ * isn't absolute/parseable.
+ */
+export function withProlificPid(
+    surveyUrl: string | undefined,
+    prolificPid: string | undefined,
+): string | undefined {
+    if (!surveyUrl || !prolificPid) return surveyUrl;
+    try {
+        const url = new URL(surveyUrl);
+        url.searchParams.set("PROLIFIC_PID", prolificPid);
+        return url.toString();
+    } catch {
+        // Non-absolute or malformed survey URL — pass through unchanged.
+        return surveyUrl;
+    }
+}