diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 955c5652e..df9b1aa07 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -34117,6 +34117,17 @@ components:
             - alphaAsc
             - alphaDesc
             - manual
+        groupBy:
+          type: string
+          enum:
+            - none
+            - category
+        groupsOpen:
+          type: string
+          enum:
+            - expanded
+            - flagged
+            - collapsed
       required:
         - version
         - list
@@ -75011,6 +75022,22 @@ components:
             - alphaDesc
             - manual
           description: Sort of the labs list; `manual` follows `order`. Default "recentDesc". The other lists ignore it.
+        groupBy:
+          type: string
+          enum:
+            - none
+            - category
+          description: 'Whether the labs list shows its server-resolved categories (`category`) or one flat list (`none`). Default
+            "none". The labs list stays flat while `GET /api/labs/overview` answers `grouped: false`. The other lists
+            ignore it.'
+        groupsOpen:
+          type: string
+          enum:
+            - expanded
+            - flagged
+            - collapsed
+          description: 'Which labs categories start open: every one (`expanded`), only those whose `status` is `above` or `below`
+            (`flagged`), or none (`collapsed`). Default "expanded". The other lists ignore it.'
         saved:
           type: boolean
           description: True when the server holds a choice for this list; false means every field is a default.
@@ -75018,6 +75045,8 @@ components:
         - view
         - order
         - sortDir
+        - groupBy
+        - groupsOpen
         - saved
       additionalProperties: false
     ModuleListLayoutSavedEnvelope:
diff --git a/src/app/api/settings/module-list-layout/route.ts b/src/app/api/settings/module-list-layout/route.ts
index afb291c57..cbf362c86 100644
--- a/src/app/api/settings/module-list-layout/route.ts
+++ b/src/app/api/settings/module-list-layout/route.ts
@@ -65,7 +65,7 @@ export const PUT = apiHandler(async (request: Request) => {
   });
   if (!parsed.ok) return parsed.error;
 
-  const { list, view, order, sortDir } = parsed.data;
+  const { list, view, order, sortDir, groupBy, groupsOpen } = parsed.data;
   // Preserve-when-absent: one stored read fills whichever field the body
   // left out, and every other list stays as stored. Only fields a person has
   // chosen are written, so a field never picked keeps following the default.
@@ -77,6 +77,8 @@ export const PUT = apiHandler(async (request: Request) => {
       ...(view ? { view } : {}),
       ...(order ? { order: [...new Set(order)] } : {}),
       ...(sortDir ? { sortDir } : {}),
+      ...(groupBy ? { groupBy } : {}),
+      ...(groupsOpen ? { groupsOpen } : {}),
     };
     const next = { ...stored, [list]: nextChoices };
     await tx.user.update({
@@ -93,6 +95,8 @@ export const PUT = apiHandler(async (request: Request) => {
       list,
       view: layout.lists[list].view,
       sortDir: layout.lists[list].sortDir,
+      groupBy: layout.lists[list].groupBy,
+      groupsOpen: layout.lists[list].groupsOpen,
       orderLength: layout.lists[list].order.length,
     },
   });
diff --git a/src/lib/__tests__/module-list-prefs.test.ts b/src/lib/__tests__/module-list-prefs.test.ts
index a156e6303..896e3d4a6 100644
--- a/src/lib/__tests__/module-list-prefs.test.ts
+++ b/src/lib/__tests__/module-list-prefs.test.ts
@@ -62,7 +62,13 @@ describe("parseModuleListPrefs", () => {
         JSON.stringify({ view: "grid", sortDir: "weird", order: ["a", "b"] }),
         defaults,
       ),
-    ).toEqual({ view: "cards", sortDir: "recentDesc", order: ["a", "b"] });
+    ).toEqual({
+      view: "cards",
+      sortDir: "recentDesc",
+      order: ["a", "b"],
+      groupBy: "none",
+      groupsOpen: "expanded",
+    });
   });
 
   it("applies the labs default (list view, #40) when nothing is stored", () => {
diff --git a/src/lib/module-list-prefs.ts b/src/lib/module-list-prefs.ts
index bbed3e12f..10e279b01 100644
--- a/src/lib/module-list-prefs.ts
+++ b/src/lib/module-list-prefs.ts
@@ -2,7 +2,7 @@
 
 /**
  * Per-list presentation for the labs, illness and checkups lists: card or
- * list view, a manual order, and (labs only) the sort.
+ * list view, a manual order, and (labs only) the sort and the categories.
  *
  * The choices live on the server (`GET/PUT /api/settings/module-list-layout`,
  * `User.moduleListLayoutJson`) so they follow a person to every device. Until
@@ -39,11 +39,15 @@ import {
   type ModuleListKey,
   type ModuleListLayout,
   type ModuleListPrefs,
+  type ModuleGroupBy,
+  type ModuleGroupsOpen,
   type ModuleListView,
   type ModuleSortDir,
 } from "@/lib/settings/module-list-layout";
 
 export type {
+  ModuleGroupBy,
+  ModuleGroupsOpen,
   ModuleListKey,
   ModuleListPrefs,
   ModuleListView,
@@ -59,7 +63,8 @@ export function legacyModuleListStorageKey(list: ModuleListKey): string {
 
 /**
  * Parse a browser-stored blob from before the server column. Anything
- * malformed collapses onto the defaults field by field.
+ * malformed collapses onto the defaults field by field. The browser never
+ * held the category fields, so those always come from the defaults.
  */
 export function parseModuleListPrefs(
   raw: string | null,
@@ -69,6 +74,7 @@ export function parseModuleListPrefs(
   try {
     const blob = JSON.parse(raw) as Record<string, unknown>;
     return {
+      ...defaults,
       view: isModuleListView(blob.view) ? blob.view : defaults.view,
       order: normaliseModuleListOrder(blob.order) ?? [],
       sortDir: isModuleSortDir(blob.sortDir) ? blob.sortDir : defaults.sortDir,
@@ -220,7 +226,12 @@ export async function runSetModuleListPrefs(deps: {
       ...patch,
     });
     if (saved) queryClient.setQueryData(key, saved);
-    if (patch.view !== undefined || patch.sortDir !== undefined) {
+    if (
+      patch.view !== undefined ||
+      patch.sortDir !== undefined ||
+      patch.groupBy !== undefined ||
+      patch.groupsOpen !== undefined
+    ) {
       toastWrittenOutcome("success", t("settings.saved"));
     }
   } catch (failure) {
@@ -238,6 +249,8 @@ export function useModuleListPrefs(list: ModuleListKey): {
   setView: (view: ModuleListView) => void;
   setOrder: (order: string[]) => void;
   setSortDir: (sortDir: ModuleSortDir) => void;
+  setGroupBy: (groupBy: ModuleGroupBy) => void;
+  setGroupsOpen: (groupsOpen: ModuleGroupsOpen) => void;
 } {
   const queryClient = useQueryClient();
   const { t } = useTranslations();
@@ -259,7 +272,13 @@ export function useModuleListPrefs(list: ModuleListKey): {
   const entry = data?.lists[list];
   const prefs = useMemo<ModuleListPrefs>(() => {
     if (entry) {
-      return { view: entry.view, order: entry.order, sortDir: entry.sortDir };
+      return {
+        view: entry.view,
+        order: entry.order,
+        sortDir: entry.sortDir,
+        groupBy: entry.groupBy,
+        groupsOpen: entry.groupsOpen,
+      };
     }
     const defaults = moduleListDefaults(list);
     if (!mounted) return defaults;
@@ -282,5 +301,14 @@ export function useModuleListPrefs(list: ModuleListKey): {
     [write],
   );
 
-  return { prefs, setView, setOrder, setSortDir };
+  const setGroupBy = useCallback(
+    (groupBy: ModuleGroupBy) => write({ groupBy }),
+    [write],
+  );
+  const setGroupsOpen = useCallback(
+    (groupsOpen: ModuleGroupsOpen) => write({ groupsOpen }),
+    [write],
+  );
+
+  return { prefs, setView, setOrder, setSortDir, setGroupBy, setGroupsOpen };
 }
diff --git a/src/lib/openapi/routes/settings.ts b/src/lib/openapi/routes/settings.ts
index 82bb91ffd..897c75a69 100644
--- a/src/lib/openapi/routes/settings.ts
+++ b/src/lib/openapi/routes/settings.ts
@@ -25,6 +25,8 @@ import {
 } from "./shared";
 import { WEBHOOK_PAYLOAD_FORMATS } from "@/lib/notifications/types";
 import {
+  MODULE_GROUPS_OPEN,
+  MODULE_GROUP_BYS,
   MODULE_LIST_VIEWS,
   MODULE_SORT_DIRS,
 } from "@/lib/settings/module-list-layout";
@@ -47,6 +49,16 @@ const moduleListPrefsEntry = z
       .describe(
         'Sort of the labs list; `manual` follows `order`. Default "recentDesc". The other lists ignore it.',
       ),
+    groupBy: z
+      .enum(MODULE_GROUP_BYS)
+      .describe(
+        'Whether the labs list shows its server-resolved categories (`category`) or one flat list (`none`). Default "none". The labs list stays flat while `GET /api/labs/overview` answers `grouped: false`. The other lists ignore it.',
+      ),
+    groupsOpen: z
+      .enum(MODULE_GROUPS_OPEN)
+      .describe(
+        'Which labs categories start open: every one (`expanded`), only those whose `status` is `above` or `below` (`flagged`), or none (`collapsed`). Default "expanded". The other lists ignore it.',
+      ),
     saved: z
       .boolean()
       .describe(
diff --git a/src/lib/settings/__tests__/module-list-layout.test.ts b/src/lib/settings/__tests__/module-list-layout.test.ts
index c431a945b..afc43656c 100644
--- a/src/lib/settings/__tests__/module-list-layout.test.ts
+++ b/src/lib/settings/__tests__/module-list-layout.test.ts
@@ -14,6 +14,8 @@ describe("resolveModuleListLayout", () => {
       view: "list",
       order: [],
       sortDir: "recentDesc",
+      groupBy: "none",
+      groupsOpen: "expanded",
       saved: false,
     });
     expect(layout.lists.illness.view).toBe("cards");
@@ -30,6 +32,8 @@ describe("resolveModuleListLayout", () => {
       view: "cards",
       order: ["b", "a"],
       sortDir: "recentDesc",
+      groupBy: "none",
+      groupsOpen: "expanded",
       saved: true,
     });
     expect(layout.lists.labs.saved).toBe(false);
@@ -44,12 +48,33 @@ describe("resolveModuleListLayout", () => {
       view: "list",
       order: [],
       sortDir: "recentDesc",
+      groupBy: "none",
+      groupsOpen: "expanded",
       saved: false,
     });
     expect(layout.lists.vorsorge.saved).toBe(false);
   });
 });
 
+describe("category choices", () => {
+  it("keeps valid category choices and drops unknown ones", () => {
+    const layout = resolveModuleListLayout({
+      labs: { groupBy: "category", groupsOpen: "flagged" },
+      illness: { groupBy: "panel", groupsOpen: "all" },
+    });
+    expect(layout.lists.labs).toMatchObject({
+      groupBy: "category",
+      groupsOpen: "flagged",
+      saved: true,
+    });
+    expect(layout.lists.illness).toMatchObject({
+      groupBy: "none",
+      groupsOpen: "expanded",
+      saved: false,
+    });
+  });
+});
+
 describe("normaliseModuleListOrder", () => {
   it("keeps strings, drops duplicates, empties and over-long ids", () => {
     expect(
diff --git a/src/lib/settings/module-list-layout.ts b/src/lib/settings/module-list-layout.ts
index d7fa5fc7c..aa7cf8881 100644
--- a/src/lib/settings/module-list-layout.ts
+++ b/src/lib/settings/module-list-layout.ts
@@ -10,6 +10,10 @@
  *   block in the server's own order.
  * - `sortDir`: only the labs list reads it (recency, alphabetical, or the
  *   manual `order`).
+ * - `groupBy` / `groupsOpen`: only the labs list reads them. `groupBy` shows
+ *   the list under its server-resolved categories (`"category"`) or flat
+ *   (`"none"`, the default); `groupsOpen` says which categories start open:
+ *   all of them, only those with a value outside its range, or none.
  *
  * Null / missing column = the defaults below. The GET never lazy-writes, and
  * the PUT stores only the fields a person has actually chosen, so a default
@@ -37,6 +41,12 @@ export const MODULE_SORT_DIRS = [
 ] as const;
 export type ModuleSortDir = (typeof MODULE_SORT_DIRS)[number];
 
+export const MODULE_GROUP_BYS = ["none", "category"] as const;
+export type ModuleGroupBy = (typeof MODULE_GROUP_BYS)[number];
+
+export const MODULE_GROUPS_OPEN = ["expanded", "flagged", "collapsed"] as const;
+export type ModuleGroupsOpen = (typeof MODULE_GROUPS_OPEN)[number];
+
 /** Longest order a list keeps; a longer one is cut, never refused. */
 export const MODULE_LIST_ORDER_MAX = 500;
 /** Longest id an order entry may carry (cuid and uuid fit comfortably). */
@@ -46,6 +56,8 @@ export interface ModuleListPrefs {
   view: ModuleListView;
   order: string[];
   sortDir: ModuleSortDir;
+  groupBy: ModuleGroupBy;
+  groupsOpen: ModuleGroupsOpen;
 }
 
 export interface ModuleListPrefsEntry extends ModuleListPrefs {
@@ -62,6 +74,8 @@ const BASE_DEFAULTS: ModuleListPrefs = {
   view: "cards",
   order: [],
   sortDir: "recentDesc",
+  groupBy: "none",
+  groupsOpen: "expanded",
 };
 
 /** Labs opens on the compact list, the dense reading table (#40). */
@@ -90,6 +104,20 @@ export function isModuleSortDir(value: unknown): value is ModuleSortDir {
   );
 }
 
+export function isModuleGroupBy(value: unknown): value is ModuleGroupBy {
+  return (
+    typeof value === "string" &&
+    (MODULE_GROUP_BYS as readonly string[]).includes(value)
+  );
+}
+
+export function isModuleGroupsOpen(value: unknown): value is ModuleGroupsOpen {
+  return (
+    typeof value === "string" &&
+    (MODULE_GROUPS_OPEN as readonly string[]).includes(value)
+  );
+}
+
 /** Keep string ids of a sane length, first occurrence wins, capped. */
 export function normaliseModuleListOrder(raw: unknown): string[] | null {
   if (!Array.isArray(raw)) return null;
@@ -114,12 +142,22 @@ export function storedModuleListChoices(
   raw: unknown,
 ): Partial<ModuleListPrefs> {
   if (raw === null || raw === undefined || typeof raw !== "object") return {};
-  const blob = raw as { view?: unknown; order?: unknown; sortDir?: unknown };
+  const blob = raw as {
+    view?: unknown;
+    order?: unknown;
+    sortDir?: unknown;
+    groupBy?: unknown;
+    groupsOpen?: unknown;
+  };
   const order = normaliseModuleListOrder(blob.order);
   return {
     ...(isModuleListView(blob.view) ? { view: blob.view } : {}),
     ...(order !== null ? { order } : {}),
     ...(isModuleSortDir(blob.sortDir) ? { sortDir: blob.sortDir } : {}),
+    ...(isModuleGroupBy(blob.groupBy) ? { groupBy: blob.groupBy } : {}),
+    ...(isModuleGroupsOpen(blob.groupsOpen)
+      ? { groupsOpen: blob.groupsOpen }
+      : {}),
   };
 }
 
diff --git a/src/lib/validations/settings-prefs.ts b/src/lib/validations/settings-prefs.ts
index 26ab7745f..70e5c231a 100644
--- a/src/lib/validations/settings-prefs.ts
+++ b/src/lib/validations/settings-prefs.ts
@@ -7,6 +7,8 @@
 import { z } from "zod/v4";
 
 import {
+  MODULE_GROUPS_OPEN,
+  MODULE_GROUP_BYS,
   MODULE_LIST_ID_MAX,
   MODULE_LIST_KEYS,
   MODULE_LIST_ORDER_MAX,
@@ -24,5 +26,7 @@ export const moduleListLayoutPutSchema = z
       .max(MODULE_LIST_ORDER_MAX)
       .optional(),
     sortDir: z.enum(MODULE_SORT_DIRS).optional(),
+    groupBy: z.enum(MODULE_GROUP_BYS).optional(),
+    groupsOpen: z.enum(MODULE_GROUPS_OPEN).optional(),
   })
   .strict();
diff --git a/tests/integration/settings-prefs-routes.test.ts b/tests/integration/settings-prefs-routes.test.ts
index b0b91739d..eda334939 100644
--- a/tests/integration/settings-prefs-routes.test.ts
+++ b/tests/integration/settings-prefs-routes.test.ts
@@ -124,6 +124,8 @@ describe("/api/settings/module-list-layout — integration", () => {
       view: "list",
       order: ["m2", "m1"],
       sortDir: "manual",
+      groupBy: "none",
+      groupsOpen: "expanded",
       saved: true,
     });
     expect(body.data.lists.illness).toMatchObject({
@@ -145,6 +147,49 @@ describe("/api/settings/module-list-layout — integration", () => {
     });
   });
 
+  it("stores the category choices and reads them back", async () => {
+    const { userId } = await seedUser();
+    const { GET, PUT } =
+      await import("@/app/api/settings/module-list-layout/route");
+    const put = await (PUT as Handler)(
+      json("PUT", URL, {
+        version: 1,
+        list: "labs",
+        groupBy: "category",
+        groupsOpen: "flagged",
+      }),
+    );
+    expect(put.status).toBe(200);
+    // A later write of another field keeps them.
+    await (PUT as Handler)(
+      json("PUT", URL, { version: 1, list: "labs", view: "cards" }),
+    );
+
+    const res = await (GET as Handler)(new Request(URL));
+    const body = (await res.json()) as {
+      data: { lists: Record<string, Record<string, unknown>> };
+    };
+    expect(body.data.lists.labs).toMatchObject({
+      view: "cards",
+      groupBy: "category",
+      groupsOpen: "flagged",
+      saved: true,
+    });
+    const row = await getPrismaClient().user.findUnique({
+      where: { id: userId },
+      select: { moduleListLayoutJson: true },
+    });
+    expect(row?.moduleListLayoutJson).toEqual({
+      version: 1,
+      labs: { groupBy: "category", groupsOpen: "flagged", view: "cards" },
+    });
+
+    const refused = await (PUT as Handler)(
+      json("PUT", URL, { version: 1, list: "labs", groupsOpen: "all" }),
+    );
+    expect(refused.status).toBe(422);
+  });
+
   it("refuses unknown lists, values and keys with every issue named", async () => {
     await seedUser();
     const { PUT } = await import("@/app/api/settings/module-list-layout/route");
diff --git a/tests/integration/settings-round-trip.test.ts b/tests/integration/settings-round-trip.test.ts
index b961fbad2..a34f34ef3 100644
--- a/tests/integration/settings-round-trip.test.ts
+++ b/tests/integration/settings-round-trip.test.ts
@@ -869,9 +869,11 @@ function entries(user: Pick<User, "id">): Entry[] {
         route: "/api/settings/module-list-layout",
         body: {
           version: 1,
-          list: "illness",
-          view: "list",
+          list: "labs",
+          view: "cards",
           sortDir: "alphaAsc",
+          groupBy: "category",
+          groupsOpen: "collapsed",
         },
       },
       read: {
@@ -881,11 +883,13 @@ function entries(user: Pick<User, "id">): Entry[] {
           route: "/api/settings/module-list-layout",
         },
         pick: (res) => [
-          at(res.data, "lists.illness.view"),
-          at(res.data, "lists.illness.sortDir"),
+          at(res.data, "lists.labs.view"),
+          at(res.data, "lists.labs.sortDir"),
+          at(res.data, "lists.labs.groupBy"),
+          at(res.data, "lists.labs.groupsOpen"),
         ],
       },
-      expected: ["list", "alphaAsc"],
+      expected: ["cards", "alphaAsc", "category", "collapsed"],
     },
     {
       columns: ["activityGoalsJson"],