diff --git a/apps/desktop/src/clientPersistence.test.ts b/apps/desktop/src/clientPersistence.test.ts
index df2178c0b0..ddaebee450 100644
--- a/apps/desktop/src/clientPersistence.test.ts
+++ b/apps/desktop/src/clientPersistence.test.ts
@@ -52,6 +52,7 @@ const clientSettings: ClientSettings = {
   confirmThreadArchive: true,
   confirmThreadDelete: false,
   diffWordWrap: true,
+  sidebarProjectsDefaultExpanded: false,
   sidebarProjectSortOrder: "manual",
   sidebarThreadSortOrder: "created_at",
   timestampFormat: "24-hour",
diff --git a/apps/web/src/components/Sidebar.tsx b/apps/web/src/components/Sidebar.tsx
index 03ae979017..629efd19e9 100644
--- a/apps/web/src/components/Sidebar.tsx
+++ b/apps/web/src/components/Sidebar.tsx
@@ -980,6 +980,9 @@ const SidebarProjectItem = memo(function SidebarProjectItem(props: SidebarProjec
   const defaultThreadEnvMode = useSettings<ThreadEnvMode>(
     (settings) => settings.defaultThreadEnvMode,
   );
+  const sidebarProjectsDefaultExpanded = useSettings<boolean>(
+    (settings) => settings.sidebarProjectsDefaultExpanded,
+  );
   const router = useRouter();
   const markThreadUnread = useUiStateStore((state) => state.markThreadUnread);
   const toggleProject = useUiStateStore((state) => state.toggleProject);
@@ -1105,7 +1108,7 @@ const SidebarProjectItem = memo(function SidebarProjectItem(props: SidebarProjec
   // already fetched into allSidebarThreads, so we can use them directly.
   const projectThreads = allSidebarThreads;
   const projectExpanded = useUiStateStore(
-    (state) => state.projectExpandedById[project.projectKey] ?? true,
+    (state) => state.projectExpandedById[project.projectKey] ?? sidebarProjectsDefaultExpanded,
   );
   const threadLastVisitedAts = useUiStateStore(
     useShallow((state) =>
@@ -1254,13 +1257,14 @@ const SidebarProjectItem = memo(function SidebarProjectItem(props: SidebarProjec
       if (selectedThreadCount > 0) {
         clearSelection();
       }
-      toggleProject(project.projectKey);
+      toggleProject(project.projectKey, sidebarProjectsDefaultExpanded);
     },
     [
       clearSelection,
       dragInProgressRef,
       project.projectKey,
       selectedThreadCount,
+      sidebarProjectsDefaultExpanded,
       suppressProjectClickAfterDragRef,
       suppressProjectClickForContextMenuRef,
       toggleProject,
@@ -1274,9 +1278,9 @@ const SidebarProjectItem = memo(function SidebarProjectItem(props: SidebarProjec
       if (dragInProgressRef.current) {
         return;
       }
-      toggleProject(project.projectKey);
+      toggleProject(project.projectKey, sidebarProjectsDefaultExpanded);
     },
-    [dragInProgressRef, project.projectKey, toggleProject],
+    [dragInProgressRef, project.projectKey, sidebarProjectsDefaultExpanded, toggleProject],
   );
 
   const handleProjectButtonPointerDownCapture = useCallback(
@@ -2364,6 +2368,7 @@ export default function Sidebar() {
   const isOnSettings = pathname.startsWith("/settings");
   const sidebarThreadSortOrder = useSettings((s) => s.sidebarThreadSortOrder);
   const sidebarProjectSortOrder = useSettings((s) => s.sidebarProjectSortOrder);
+  const sidebarProjectsDefaultExpanded = useSettings((s) => s.sidebarProjectsDefaultExpanded);
   const defaultThreadEnvMode = useSettings((s) => s.defaultThreadEnvMode);
   const { updateSettings } = useUpdateSettings();
   const { handleNewThread } = useNewThreadHandler();
@@ -2804,7 +2809,7 @@ export default function Sidebar() {
           ),
           sidebarThreadSortOrder,
         );
-        const projectExpanded = projectExpandedById[project.projectKey] ?? true;
+        const projectExpanded = projectExpandedById[project.projectKey] ?? sidebarProjectsDefaultExpanded;
         const activeThreadKey = routeThreadKey ?? undefined;
         const pinnedCollapsedThread =
           !projectExpanded && activeThreadKey
@@ -2831,6 +2836,7 @@ export default function Sidebar() {
       }),
     [
       sidebarThreadSortOrder,
+      sidebarProjectsDefaultExpanded,
       expandedThreadListsByProject,
       projectExpandedById,
       routeThreadKey,
diff --git a/apps/web/src/components/settings/SettingsPanels.tsx b/apps/web/src/components/settings/SettingsPanels.tsx
index c8766f2643..acdd3ac57f 100644
--- a/apps/web/src/components/settings/SettingsPanels.tsx
+++ b/apps/web/src/components/settings/SettingsPanels.tsx
@@ -383,6 +383,10 @@ export function useSettingsRestore(onRestored?: () => void) {
       ...(settings.confirmThreadDelete !== DEFAULT_UNIFIED_SETTINGS.confirmThreadDelete
         ? ["Delete confirmation"]
         : []),
+      ...(settings.sidebarProjectsDefaultExpanded !==
+      DEFAULT_UNIFIED_SETTINGS.sidebarProjectsDefaultExpanded
+        ? ["Expand projects on startup"]
+        : []),
       ...(isGitWritingModelDirty ? ["Git writing model"] : []),
       ...(areProviderSettingsDirty ? ["Providers"] : []),
     ],
@@ -394,6 +398,7 @@ export function useSettingsRestore(onRestored?: () => void) {
       settings.defaultThreadEnvMode,
       settings.diffWordWrap,
       settings.enableAssistantStreaming,
+      settings.sidebarProjectsDefaultExpanded,
       settings.timestampFormat,
       theme,
     ],
@@ -904,6 +909,34 @@ export function GeneralSettingsPanel() {
           }
         />
 
+        <SettingsRow
+          title="Expand projects on startup"
+          description="Show project threads expanded in the sidebar when the app starts."
+          resetAction={
+            settings.sidebarProjectsDefaultExpanded !==
+            DEFAULT_UNIFIED_SETTINGS.sidebarProjectsDefaultExpanded ? (
+              <SettingResetButton
+                label="expand projects on startup"
+                onClick={() =>
+                  updateSettings({
+                    sidebarProjectsDefaultExpanded:
+                      DEFAULT_UNIFIED_SETTINGS.sidebarProjectsDefaultExpanded,
+                  })
+                }
+              />
+            ) : null
+          }
+          control={
+            <Switch
+              checked={settings.sidebarProjectsDefaultExpanded}
+              onCheckedChange={(checked) =>
+                updateSettings({ sidebarProjectsDefaultExpanded: Boolean(checked) })
+              }
+              aria-label="Expand projects on startup"
+            />
+          }
+        />
+
         <SettingsRow
           title="Text generation model"
           description="Configure the model used for generated commit messages, PR titles, and similar Git text."
diff --git a/apps/web/src/environments/runtime/service.ts b/apps/web/src/environments/runtime/service.ts
index 5c8d2dacab..b330f61cf5 100644
--- a/apps/web/src/environments/runtime/service.ts
+++ b/apps/web/src/environments/runtime/service.ts
@@ -57,6 +57,7 @@ import {
   selectThreadsAcrossEnvironments,
 } from "~/store";
 import { useTerminalStateStore } from "~/terminalStateStore";
+import { getClientSettingsSnapshot } from "~/hooks/useSettings";
 import { useUiStateStore } from "~/uiStateStore";
 import { WsTransport } from "../../rpc/wsTransport";
 import { createWsRpcClient, type WsRpcClient } from "../../rpc/wsRpcClient";
@@ -179,6 +180,7 @@ function reconcileSnapshotDerivedState() {
       key: scopedProjectKey(scopeProjectRef(project.environmentId, project.id)),
       cwd: project.cwd,
     })),
+    getClientSettingsSnapshot().sidebarProjectsDefaultExpanded,
   );
   useUiStateStore.getState().syncThreads(
     threads.map((thread) => ({
@@ -242,6 +244,7 @@ function applyRecoveredEventBatch(
         key: scopedProjectKey(scopeProjectRef(project.environmentId, project.id)),
         cwd: project.cwd,
       })),
+      getClientSettingsSnapshot().sidebarProjectsDefaultExpanded,
     );
   }
 
diff --git a/apps/web/src/hooks/useSettings.ts b/apps/web/src/hooks/useSettings.ts
index 3dc2cf9b20..8b7b472f5b 100644
--- a/apps/web/src/hooks/useSettings.ts
+++ b/apps/web/src/hooks/useSettings.ts
@@ -35,7 +35,7 @@ function emitClientSettingsChange() {
   }
 }
 
-function getClientSettingsSnapshot(): ClientSettings {
+export function getClientSettingsSnapshot(): ClientSettings {
   return clientSettingsSnapshot;
 }
 
diff --git a/apps/web/src/localApi.test.ts b/apps/web/src/localApi.test.ts
index 3883d77c8d..6dfdb677ab 100644
--- a/apps/web/src/localApi.test.ts
+++ b/apps/web/src/localApi.test.ts
@@ -503,6 +503,7 @@ describe("wsApi", () => {
       confirmThreadArchive: true,
       confirmThreadDelete: false,
       diffWordWrap: true,
+      sidebarProjectsDefaultExpanded: false,
       sidebarProjectSortOrder: "manual",
       sidebarThreadSortOrder: "created_at",
       timestampFormat: "24-hour",
@@ -531,6 +532,7 @@ describe("wsApi", () => {
       confirmThreadArchive: true,
       confirmThreadDelete: false,
       diffWordWrap: true,
+      sidebarProjectsDefaultExpanded: false,
       sidebarProjectSortOrder: "manual",
       sidebarThreadSortOrder: "created_at",
       timestampFormat: "24-hour",
@@ -549,6 +551,7 @@ describe("wsApi", () => {
       confirmThreadArchive: true,
       confirmThreadDelete: false,
       diffWordWrap: true,
+      sidebarProjectsDefaultExpanded: false,
       sidebarProjectSortOrder: "manual",
       sidebarThreadSortOrder: "created_at",
       timestampFormat: "24-hour",
@@ -568,6 +571,7 @@ describe("wsApi", () => {
       confirmThreadArchive: true,
       confirmThreadDelete: false,
       diffWordWrap: true,
+      sidebarProjectsDefaultExpanded: false,
       sidebarProjectSortOrder: "manual",
       sidebarThreadSortOrder: "created_at",
       timestampFormat: "24-hour",
@@ -592,6 +596,7 @@ describe("wsApi", () => {
       confirmThreadDelete: false,
       diffWordWrap: true,
       sidebarProjectSortOrder: "manual",
+      sidebarProjectsDefaultExpanded: false,
       sidebarThreadSortOrder: "created_at",
       timestampFormat: "24-hour",
     });
diff --git a/apps/web/src/uiStateStore.ts b/apps/web/src/uiStateStore.ts
index 7ae7232063..cfa4c4f1e3 100644
--- a/apps/web/src/uiStateStore.ts
+++ b/apps/web/src/uiStateStore.ts
@@ -209,7 +209,11 @@ function nestedBooleanRecordsEqual(
   return true;
 }
 
-export function syncProjects(state: UiState, projects: readonly SyncProjectInput[]): UiState {
+export function syncProjects(
+  state: UiState,
+  projects: readonly SyncProjectInput[],
+  defaultExpanded = false,
+): UiState {
   const previousProjectCwdById = new Map(currentProjectCwdById);
   const previousProjectIdByCwd = new Map(
     [...previousProjectCwdById.entries()].map(([projectId, cwd]) => [cwd, projectId] as const),
@@ -234,7 +238,7 @@ export function syncProjects(state: UiState, projects: readonly SyncProjectInput
       (previousProjectIdForCwd ? previousExpandedById[previousProjectIdForCwd] : undefined) ??
       (persistedExpandedProjectCwds.size > 0
         ? persistedExpandedProjectCwds.has(project.cwd)
-        : true);
+        : defaultExpanded);
     nextExpandedById[project.key] = expanded;
     return {
       id: project.key,
@@ -456,8 +460,8 @@ export function setThreadChangedFilesExpanded(
   };
 }
 
-export function toggleProject(state: UiState, projectId: string): UiState {
-  const expanded = state.projectExpandedById[projectId] ?? true;
+export function toggleProject(state: UiState, projectId: string, defaultExpanded = false): UiState {
+  const expanded = state.projectExpandedById[projectId] ?? defaultExpanded;
   return {
     ...state,
     projectExpandedById: {
@@ -467,8 +471,12 @@ export function toggleProject(state: UiState, projectId: string): UiState {
   };
 }
 
-export function setProjectExpanded(state: UiState, projectId: string, expanded: boolean): UiState {
-  if ((state.projectExpandedById[projectId] ?? true) === expanded) {
+export function setProjectExpanded(
+  state: UiState,
+  projectId: string,
+  expanded: boolean,
+): UiState {
+  if (state.projectExpandedById[projectId] === expanded) {
     return state;
   }
   return {
@@ -524,13 +532,13 @@ export function reorderProjects(
 }
 
 interface UiStateStore extends UiState {
-  syncProjects: (projects: readonly SyncProjectInput[]) => void;
+  syncProjects: (projects: readonly SyncProjectInput[], defaultExpanded?: boolean) => void;
   syncThreads: (threads: readonly SyncThreadInput[]) => void;
   markThreadVisited: (threadId: string, visitedAt?: string) => void;
   markThreadUnread: (threadId: string, latestTurnCompletedAt: string | null | undefined) => void;
   clearThreadUi: (threadId: string) => void;
   setThreadChangedFilesExpanded: (threadId: string, turnId: string, expanded: boolean) => void;
-  toggleProject: (projectId: string) => void;
+  toggleProject: (projectId: string, defaultExpanded?: boolean) => void;
   setProjectExpanded: (projectId: string, expanded: boolean) => void;
   reorderProjects: (
     draggedProjectIds: readonly string[],
@@ -540,7 +548,8 @@ interface UiStateStore extends UiState {
 
 export const useUiStateStore = create<UiStateStore>((set) => ({
   ...readPersistedState(),
-  syncProjects: (projects) => set((state) => syncProjects(state, projects)),
+  syncProjects: (projects, defaultExpanded) =>
+    set((state) => syncProjects(state, projects, defaultExpanded)),
   syncThreads: (threads) => set((state) => syncThreads(state, threads)),
   markThreadVisited: (threadId, visitedAt) =>
     set((state) => markThreadVisited(state, threadId, visitedAt)),
@@ -549,7 +558,8 @@ export const useUiStateStore = create<UiStateStore>((set) => ({
   clearThreadUi: (threadId) => set((state) => clearThreadUi(state, threadId)),
   setThreadChangedFilesExpanded: (threadId, turnId, expanded) =>
     set((state) => setThreadChangedFilesExpanded(state, threadId, turnId, expanded)),
-  toggleProject: (projectId) => set((state) => toggleProject(state, projectId)),
+  toggleProject: (projectId, defaultExpanded) =>
+    set((state) => toggleProject(state, projectId, defaultExpanded)),
   setProjectExpanded: (projectId, expanded) =>
     set((state) => setProjectExpanded(state, projectId, expanded)),
   reorderProjects: (draggedProjectIds, targetProjectIds) =>
diff --git a/packages/contracts/src/settings.ts b/packages/contracts/src/settings.ts
index 426f8bee56..1a5ae2e967 100644
--- a/packages/contracts/src/settings.ts
+++ b/packages/contracts/src/settings.ts
@@ -27,6 +27,9 @@ export const ClientSettingsSchema = Schema.Struct({
   confirmThreadArchive: Schema.Boolean.pipe(Schema.withDecodingDefault(Effect.succeed(false))),
   confirmThreadDelete: Schema.Boolean.pipe(Schema.withDecodingDefault(Effect.succeed(true))),
   diffWordWrap: Schema.Boolean.pipe(Schema.withDecodingDefault(Effect.succeed(false))),
+  sidebarProjectsDefaultExpanded: Schema.Boolean.pipe(
+    Schema.withDecodingDefault(Effect.succeed(false)),
+  ),
   sidebarProjectSortOrder: SidebarProjectSortOrder.pipe(
     Schema.withDecodingDefault(Effect.succeed(DEFAULT_SIDEBAR_PROJECT_SORT_ORDER)),
   ),