diff --git a/apps/web/src/components/Sidebar.tsx b/apps/web/src/components/Sidebar.tsx
index cffab8bd577..7fad851b2ea 100644
--- a/apps/web/src/components/Sidebar.tsx
+++ b/apps/web/src/components/Sidebar.tsx
@@ -9,6 +9,7 @@ import {
   LoaderIcon,
   SearchIcon,
   SquarePenIcon,
+  StarIcon,
   TerminalIcon,
   TriangleAlertIcon,
 } from "lucide-react";
@@ -367,6 +368,7 @@ export const SidebarThreadRow = memo(function SidebarThreadRow(props: SidebarThr
   } = props;
   const threadRef = scopeThreadRef(thread.environmentId, thread.id);
   const threadKey = scopedThreadKey(threadRef);
+  const isFavorite = useUiStateStore((state) => state.favoriteThreadKeys.includes(threadKey));
   const lastVisitedAt = useUiStateStore((state) => state.threadLastVisitedAtById[threadKey]);
   const isSelected = useThreadSelectionStore((state) => state.selectedThreadKeys.has(threadKey));
   const runningTerminalIds = useThreadRunningTerminalIds({
@@ -823,6 +825,12 @@ export const SidebarThreadRow = memo(function SidebarThreadRow(props: SidebarThr
                 </Tooltip>
               )
             ) : null}
+            {isFavorite ? (
+              <StarIcon
+                aria-label="Favorite"
+                className="mr-1 size-3 shrink-0 fill-amber-400 text-amber-500 dark:fill-amber-300 dark:text-amber-400"
+              />
+            ) : null}
             <span className={threadMetaClassName}>
               <span className="inline-flex items-center gap-1">
                 {isRemoteThread && !isDesktopLocalThread && (
@@ -1116,6 +1124,7 @@ const SidebarProjectItem = memo(function SidebarProjectItem(props: SidebarProjec
   const router = useRouter();
   const { isMobile, setOpenMobile } = useSidebar();
   const markThreadUnread = useUiStateStore((state) => state.markThreadUnread);
+  const toggleThreadFavorite = useUiStateStore((state) => state.toggleThreadFavorite);
   const setProjectExpanded = useUiStateStore((state) => state.setProjectExpanded);
   const toggleThreadSelection = useThreadSelectionStore((state) => state.toggleThread);
   const rangeSelectTo = useThreadSelectionStore((state) => state.rangeSelectTo);
@@ -2117,6 +2126,12 @@ const SidebarProjectItem = memo(function SidebarProjectItem(props: SidebarProjec
             ? [{ id: "new-thread-on-branch", label: `New thread on ${thread.branch}` }]
             : []),
           { id: "rename", label: "Rename thread" },
+          {
+            id: "toggle-favorite",
+            label: useUiStateStore.getState().favoriteThreadKeys.includes(threadKey)
+              ? "Remove from favorites"
+              : "Add to favorites",
+          },
           { id: "mark-unread", label: "Mark unread" },
           { id: "copy-path", label: "Copy Path" },
           { id: "copy-thread-id", label: "Copy Thread ID" },
@@ -2154,6 +2169,11 @@ const SidebarProjectItem = memo(function SidebarProjectItem(props: SidebarProjec
         return;
       }
 
+      if (clicked === "toggle-favorite") {
+        toggleThreadFavorite(threadKey);
+        return;
+      }
+
       if (clicked === "mark-unread") {
         markThreadUnread(threadKey, thread.latestTurn?.completedAt);
         return;
@@ -2210,6 +2230,7 @@ const SidebarProjectItem = memo(function SidebarProjectItem(props: SidebarProjec
       memberProjectByScopedKey,
       project.workspaceRoot,
       startThreadRename,
+      toggleThreadFavorite,
     ],
   );
 
diff --git a/apps/web/src/components/SidebarV2.tsx b/apps/web/src/components/SidebarV2.tsx
index ee73b570514..dd5c8f30f61 100644
--- a/apps/web/src/components/SidebarV2.tsx
+++ b/apps/web/src/components/SidebarV2.tsx
@@ -32,6 +32,7 @@ import {
   SearchIcon,
   ServerIcon,
   SquarePenIcon,
+  StarIcon,
   TerminalIcon,
   Trash2Icon,
   Undo2Icon,
@@ -445,6 +446,7 @@ const SidebarV2Row = memo(function SidebarV2Row(props: {
     [thread.environmentId, thread.id],
   );
   const threadKey = scopedThreadKey(threadRef);
+  const isFavorite = useUiStateStore((state) => state.favoriteThreadKeys.includes(threadKey));
   const isRegeneratingTitle = thread.titleRegeneration != null;
   const lastVisitedAt = useUiStateStore((state) => state.threadLastVisitedAtById[threadKey]);
   const isSelected = useThreadSelectionStore((state) => state.selectedThreadKeys.has(threadKey));
@@ -829,6 +831,12 @@ const SidebarV2Row = memo(function SidebarV2Row(props: {
               remain visible AND clickable while the row is hovered. Only
               the time/jump label yields to the settle affordance. */}
             {prBadge}
+            {isFavorite ? (
+              <StarIcon
+                aria-label="Favorite"
+                className="size-3 shrink-0 fill-amber-400 text-amber-500 dark:fill-amber-300 dark:text-amber-400"
+              />
+            ) : null}
             <span className="relative ml-auto flex h-6 min-w-8 shrink-0 items-center justify-end">
               <span className="inline-flex justify-end tabular-nums text-muted-foreground/55 transition-opacity group-hover/v2-row:opacity-0">
                 {variantAction === "unsnooze" && props.snoozeWakeLabelText !== null ? (
@@ -937,6 +945,12 @@ const SidebarV2Row = memo(function SidebarV2Row(props: {
               ) : (
                 <span className="flex-1" />
               )}
+              {isFavorite ? (
+                <StarIcon
+                  aria-label="Favorite"
+                  className="size-3 shrink-0 fill-amber-400 text-amber-500 dark:fill-amber-300 dark:text-amber-400"
+                />
+              ) : null}
               {/* The visible state owns this slot's width: status at rest,
                   actions on hover/focus or while the popover is open. Keeping
                   the hidden state out of flow lets the project label reclaim
@@ -1244,6 +1258,7 @@ export default function SidebarV2() {
   const toggleThreadSelection = useThreadSelectionStore((s) => s.toggleThread);
   const rangeSelectTo = useThreadSelectionStore((s) => s.rangeSelectTo);
   const markThreadUnread = useUiStateStore((s) => s.markThreadUnread);
+  const toggleThreadFavorite = useUiStateStore((s) => s.toggleThreadFavorite);
   const routeTarget = useParams({
     strict: false,
     select: (params) => resolveThreadRouteTarget(params),
@@ -2335,6 +2350,12 @@ export default function SidebarV2() {
                   ]
                 : []),
               { id: "rename", label: "Rename thread" },
+              {
+                id: "toggle-favorite",
+                label: useUiStateStore.getState().favoriteThreadKeys.includes(threadKey)
+                  ? "Remove from favorites"
+                  : "Add to favorites",
+              },
               ...(supportsTitleRegeneration
                 ? [
                     {
@@ -2396,6 +2417,9 @@ export default function SidebarV2() {
           case "rename":
             startThreadRename(threadRef, thread.title);
             return;
+          case "toggle-favorite":
+            toggleThreadFavorite(threadKey);
+            return;
           case "regenerate-title": {
             if (isRegeneratingTitle) return;
             const result = await updateThreadMetadata({
@@ -2480,6 +2504,7 @@ export default function SidebarV2() {
       projectCwdByKey,
       serverConfigs,
       startThreadRename,
+      toggleThreadFavorite,
       updateThreadMetadata,
     ],
   );
diff --git a/apps/web/src/uiStateStore.test.ts b/apps/web/src/uiStateStore.test.ts
index 30450287353..f9904f15aa9 100644
--- a/apps/web/src/uiStateStore.test.ts
+++ b/apps/web/src/uiStateStore.test.ts
@@ -14,6 +14,7 @@ import {
   setDefaultAdvertisedEndpointKey,
   setProjectExpanded,
   setThreadChangedFilesExpanded,
+  toggleThreadFavorite,
   type UiState,
 } from "./uiStateStore";
 
@@ -21,6 +22,7 @@ function makeUiState(overrides: Partial<UiState> = {}): UiState {
   return {
     projectExpandedById: {},
     projectOrder: [],
+    favoriteThreadKeys: [],
     threadLastVisitedAtById: {},
     threadChangedFilesExpandedById: {},
     defaultAdvertisedEndpointKey: null,
@@ -53,6 +55,15 @@ describe("uiStateStore pure functions", () => {
     expect(markThreadUnread(next, threadId, null)).toBe(next);
   });
 
+  it("toggles a favorite thread by its scoped key", () => {
+    const initialState = makeUiState();
+    const favorite = toggleThreadFavorite(initialState, "environment:thread-1");
+
+    expect(favorite.favoriteThreadKeys).toEqual(["environment:thread-1"]);
+    expect(toggleThreadFavorite(favorite, "environment:thread-1").favoriteThreadKeys).toEqual([]);
+    expect(toggleThreadFavorite(initialState, "")).toBe(initialState);
+  });
+
   it("resolves project expansion from logical, physical, and legacy preference keys", () => {
     const physicalKey = "environment:/repo/project";
     const legacyKey = legacyProjectCwdPreferenceKey("/repo/project");
@@ -154,6 +165,7 @@ describe("parsePersistedState", () => {
         invalid: "no" as unknown as boolean,
       },
       projectOrder: ["physical-b", "", "physical-a", "physical-b"],
+      favoriteThreadKeys: ["environment:thread-1", "", "environment:thread-1"],
       threadLastVisitedAtById: {
         "environment:thread-1": "2026-02-25T12:35:00.000Z",
         invalid: "not-a-date",
@@ -173,6 +185,7 @@ describe("parsePersistedState", () => {
         logical: false,
       },
       projectOrder: ["physical-b", "physical-a"],
+      favoriteThreadKeys: ["environment:thread-1"],
       threadLastVisitedAtById: {
         "environment:thread-1": "2026-02-25T12:35:00.000Z",
       },
@@ -270,6 +283,7 @@ describe("uiStateStore persistence", () => {
         logical: false,
       },
       projectOrder: ["physical-b", "physical-a"],
+      favoriteThreadKeys: ["environment:thread-1"],
       threadLastVisitedAtById: {
         "environment:thread-1": "2026-02-25T12:35:00.000Z",
       },
@@ -292,6 +306,7 @@ describe("uiStateStore persistence", () => {
         logical: false,
       },
       projectOrder: ["physical-b", "physical-a"],
+      favoriteThreadKeys: ["environment:thread-1"],
       threadLastVisitedAtById: {
         "environment:thread-1": "2026-02-25T12:35:00.000Z",
       },
diff --git a/apps/web/src/uiStateStore.ts b/apps/web/src/uiStateStore.ts
index 5d744d540a5..902ec9e07d9 100644
--- a/apps/web/src/uiStateStore.ts
+++ b/apps/web/src/uiStateStore.ts
@@ -20,6 +20,7 @@ const LEGACY_PERSISTED_STATE_KEYS = [
 export interface PersistedUiState {
   projectExpandedById?: Record<string, boolean>;
   projectOrder?: string[];
+  favoriteThreadKeys?: string[];
   threadLastVisitedAtById?: Record<string, string>;
   collapsedProjectCwds?: string[];
   expandedProjectCwds?: string[];
@@ -35,6 +36,7 @@ export interface UiProjectState {
 }
 
 export interface UiThreadState {
+  favoriteThreadKeys: string[];
   threadLastVisitedAtById: Record<string, string>;
   threadChangedFilesExpandedById: Record<string, Record<string, boolean>>;
 }
@@ -48,6 +50,7 @@ export interface UiState extends UiProjectState, UiThreadState, UiEndpointState
 const initialState: UiState = {
   projectExpandedById: {},
   projectOrder: [],
+  favoriteThreadKeys: [],
   threadLastVisitedAtById: {},
   threadChangedFilesExpandedById: {},
   defaultAdvertisedEndpointKey: null,
@@ -125,6 +128,7 @@ export function parsePersistedState(parsed: PersistedUiState): UiState {
   return {
     projectExpandedById,
     projectOrder,
+    favoriteThreadKeys: sanitizeStringArray(parsed.favoriteThreadKeys),
     threadLastVisitedAtById: sanitizeTimestampRecord(parsed.threadLastVisitedAtById),
     threadChangedFilesExpandedById:
       parsed.threadChangedFilesExpansionVersion === THREAD_CHANGED_FILES_EXPANSION_VERSION
@@ -203,6 +207,7 @@ export function persistState(state: UiState): void {
       JSON.stringify({
         projectExpandedById,
         projectOrder: state.projectOrder,
+        favoriteThreadKeys: state.favoriteThreadKeys,
         threadLastVisitedAtById: state.threadLastVisitedAtById,
         defaultAdvertisedEndpointKey: state.defaultAdvertisedEndpointKey,
         threadChangedFilesExpansionVersion: THREAD_CHANGED_FILES_EXPANSION_VERSION,
@@ -245,6 +250,19 @@ export function markThreadVisited(state: UiState, threadId: string, visitedAt: s
   };
 }
 
+export function toggleThreadFavorite(state: UiState, threadKey: string): UiState {
+  if (!threadKey) {
+    return state;
+  }
+  const isFavorite = state.favoriteThreadKeys.includes(threadKey);
+  return {
+    ...state,
+    favoriteThreadKeys: isFavorite
+      ? state.favoriteThreadKeys.filter((key) => key !== threadKey)
+      : [...state.favoriteThreadKeys, threadKey],
+  };
+}
+
 export function markThreadUnread(
   state: UiState,
   threadId: string,
@@ -382,6 +400,7 @@ export function reorderProjects(
 }
 
 interface UiStateStore extends UiState {
+  toggleThreadFavorite: (threadKey: string) => void;
   markThreadVisited: (threadId: string, visitedAt: string) => void;
   markThreadUnread: (threadId: string, latestTurnCompletedAt: string | null | undefined) => void;
   setThreadChangedFilesExpanded: (threadId: string, turnId: string, expanded: boolean) => void;
@@ -396,6 +415,7 @@ interface UiStateStore extends UiState {
 
 export const useUiStateStore = create<UiStateStore>((set) => ({
   ...readPersistedState(),
+  toggleThreadFavorite: (threadKey) => set((state) => toggleThreadFavorite(state, threadKey)),
   markThreadVisited: (threadId, visitedAt) =>
     set((state) => markThreadVisited(state, threadId, visitedAt)),
   markThreadUnread: (threadId, latestTurnCompletedAt) =>