diff --git a/apps/web/src/components/AppSidebarLayout.tsx b/apps/web/src/components/AppSidebarLayout.tsx
index ce42ccb038c..4098fc3fedf 100644
--- a/apps/web/src/components/AppSidebarLayout.tsx
+++ b/apps/web/src/components/AppSidebarLayout.tsx
@@ -1,11 +1,14 @@
 import { lazy, Suspense, useEffect, useState, type ReactNode } from "react";
 
 import ThreadSidebar from "./Sidebar";
-import { Sidebar, SidebarProvider, SidebarRail } from "./ui/sidebar";
+import { Sidebar, SidebarProvider, SidebarRail, useSidebar } from "./ui/sidebar";
 import {
   clearShortcutModifierState,
   syncShortcutModifierStateFromKeyboardEvent,
 } from "../shortcutModifierState";
+import { resolveShortcutCommand, shouldIgnoreGlobalNavigationShortcut } from "../keybindings";
+import { isTerminalFocused } from "../lib/terminalFocus";
+import { useServerKeybindings } from "../rpc/serverState";
 import { useSettingsDialogStore } from "../settingsDialogStore";
 
 const THREAD_SIDEBAR_WIDTH_STORAGE_KEY = "chat_thread_sidebar_width";
@@ -37,6 +40,42 @@ function LazySettingsDialogMount() {
   );
 }
 
+// The sidebar writes its open/closed state to the `sidebar_state` cookie; read
+// it back here so the collapsed state persists across reloads (SidebarProvider
+// only seeds its initial state from `defaultOpen`).
+function readSidebarOpenPreference(): boolean {
+  if (typeof document === "undefined") return true;
+  const match = document.cookie.match(/(?:^|;\s*)sidebar_state=([^;]+)/);
+  return match ? match[1] !== "false" : true;
+}
+
+// Global Mod+B (configurable as `sidebar.toggle`) handler. Lives inside the
+// SidebarProvider so the toggle works on every route — chat, settings, and the
+// no-active-thread state — not just inside the chat view's shortcut handler.
+function SidebarToggleShortcut() {
+  const { toggleSidebar } = useSidebar();
+  const keybindings = useServerKeybindings();
+
+  useEffect(() => {
+    const handler = (event: KeyboardEvent) => {
+      if (event.defaultPrevented) return;
+      const command = resolveShortcutCommand(event, keybindings, {
+        context: { terminalFocus: isTerminalFocused() },
+      });
+      if (command !== "sidebar.toggle") return;
+      // Don't steal the shortcut while typing (e.g. Mod+B for bold in the composer).
+      if (shouldIgnoreGlobalNavigationShortcut(event)) return;
+      event.preventDefault();
+      event.stopPropagation();
+      toggleSidebar();
+    };
+    window.addEventListener("keydown", handler);
+    return () => window.removeEventListener("keydown", handler);
+  }, [keybindings, toggleSidebar]);
+
+  return null;
+}
+
 export function AppSidebarLayout({ children }: { children: ReactNode }) {
   const openSettings = useSettingsDialogStore((s) => s.openSettings);
 
@@ -80,7 +119,8 @@ export function AppSidebarLayout({ children }: { children: ReactNode }) {
   }, [openSettings]);
 
   return (
-    <SidebarProvider className="h-dvh! min-h-0!" defaultOpen>
+    <SidebarProvider className="h-dvh! min-h-0!" defaultOpen={readSidebarOpenPreference()}>
+      <SidebarToggleShortcut />
       <Sidebar
         side="left"
         collapsible="offcanvas"
diff --git a/apps/web/src/components/NoActiveThreadState.tsx b/apps/web/src/components/NoActiveThreadState.tsx
index ba71f0e31b3..64081ecbc14 100644
--- a/apps/web/src/components/NoActiveThreadState.tsx
+++ b/apps/web/src/components/NoActiveThreadState.tsx
@@ -21,7 +21,7 @@ export function NoActiveThreadState() {
             </span>
           ) : (
             <div className="flex items-center gap-2">
-              <SidebarTrigger className="size-7 shrink-0 md:hidden" />
+              <SidebarTrigger className="size-7 shrink-0 group-data-[state=expanded]/sidebar-wrapper:md:hidden" />
               <span className="text-sm font-medium text-foreground md:text-muted-foreground/60">
                 No active thread
               </span>
diff --git a/apps/web/src/components/chat/ChatHeader.tsx b/apps/web/src/components/chat/ChatHeader.tsx
index c67ad91396f..65fbb3491d0 100644
--- a/apps/web/src/components/chat/ChatHeader.tsx
+++ b/apps/web/src/components/chat/ChatHeader.tsx
@@ -146,7 +146,7 @@ export const ChatHeader = memo(function ChatHeader(props: ChatHeaderProps) {
   return (
     <div className="flex min-w-0 flex-1 flex-col">
       <div className="flex min-w-0 items-center gap-2 pt-4 pb-2.5">
-        <SidebarTrigger className="size-7 shrink-0 md:hidden" />
+        <SidebarTrigger className="size-7 shrink-0 group-data-[state=expanded]/sidebar-wrapper:md:hidden" />
         <ChatHeaderBar
           projectName={props.activeProjectName}
           isGitRepo={props.isGitRepo}
diff --git a/apps/web/src/components/ui/sidebar.tsx b/apps/web/src/components/ui/sidebar.tsx
index 32206be7080..e6efa71f2b2 100644
--- a/apps/web/src/components/ui/sidebar.tsx
+++ b/apps/web/src/components/ui/sidebar.tsx
@@ -155,6 +155,7 @@ function SidebarProvider({
           className,
         )}
         data-slot="sidebar-wrapper"
+        data-state={state}
         style={
           {
             "--sidebar-width": SIDEBAR_WIDTH,
diff --git a/apps/web/src/keybindings.test.ts b/apps/web/src/keybindings.test.ts
index 44b5ed26547..e8791114d01 100644
--- a/apps/web/src/keybindings.test.ts
+++ b/apps/web/src/keybindings.test.ts
@@ -129,6 +129,11 @@ const DEFAULT_BINDINGS = compile([
     command: "commandPalette.toggle",
     whenAst: whenNot(whenIdentifier("terminalFocus")),
   },
+  {
+    shortcut: modShortcut("b"),
+    command: "sidebar.toggle",
+    whenAst: whenNot(whenIdentifier("terminalFocus")),
+  },
   {
     shortcut: modShortcut("m", { shiftKey: true }),
     command: "modelPicker.toggle",
@@ -318,6 +323,10 @@ describe("shortcutLabelForCommand", () => {
       shortcutLabelForCommand(DEFAULT_BINDINGS, "commandPalette.toggle", "MacIntel"),
       "⌘K",
     );
+    assert.strictEqual(
+      shortcutLabelForCommand(DEFAULT_BINDINGS, "sidebar.toggle", "MacIntel"),
+      "⌘B",
+    );
     assert.strictEqual(
       shortcutLabelForCommand(DEFAULT_BINDINGS, "modelPicker.toggle", "Linux"),
       "Ctrl+Shift+M",
@@ -505,6 +514,23 @@ describe("chat/editor shortcuts", () => {
     );
   });
 
+  it("matches sidebar.toggle (Mod+B) outside terminal focus", () => {
+    assert.strictEqual(
+      resolveShortcutCommand(event({ key: "b", metaKey: true }), DEFAULT_BINDINGS, {
+        platform: "MacIntel",
+        context: { terminalFocus: false },
+      }),
+      "sidebar.toggle",
+    );
+    assert.notStrictEqual(
+      resolveShortcutCommand(event({ key: "b", metaKey: true }), DEFAULT_BINDINGS, {
+        platform: "MacIntel",
+        context: { terminalFocus: true },
+      }),
+      "sidebar.toggle",
+    );
+  });
+
   it("matches diff.toggle shortcut outside terminal focus", () => {
     assert.isTrue(
       isDiffToggleShortcut(event({ key: "d", metaKey: true }), DEFAULT_BINDINGS, {
diff --git a/apps/web/src/lib/keybindingCategories.ts b/apps/web/src/lib/keybindingCategories.ts
index 571ad814abc..5996c49d866 100644
--- a/apps/web/src/lib/keybindingCategories.ts
+++ b/apps/web/src/lib/keybindingCategories.ts
@@ -11,6 +11,7 @@ export const KEYBINDING_CATEGORIES: Record<string, KeybindingCategory> = {
   workspace: { id: "workspace", label: "Workspace", sortWeight: 20 },
   diff: { id: "diff", label: "Diff", sortWeight: 30 },
   commandPalette: { id: "commandPalette", label: "Command palette", sortWeight: 40 },
+  sidebar: { id: "sidebar", label: "Sidebar", sortWeight: 45 },
   chat: { id: "chat", label: "Chat", sortWeight: 50 },
   editor: { id: "editor", label: "Editor", sortWeight: 60 },
   modelPicker: { id: "modelPicker", label: "Model picker", sortWeight: 70 },
@@ -34,6 +35,7 @@ const STATIC_COMMAND_META: Record<string, Omit<KeybindingCommandMeta, "category"
   "workspace.terminal": { title: "Open workspace terminal", sortWeight: 3 },
   "diff.toggle": { title: "Toggle diff view", sortWeight: 1 },
   "commandPalette.toggle": { title: "Open command palette", sortWeight: 1 },
+  "sidebar.toggle": { title: "Toggle sidebar", sortWeight: 1 },
   "chat.new": { title: "New chat", sortWeight: 1 },
   "chat.newLocal": { title: "New chat (local environment)", sortWeight: 2 },
   "editor.openFavorite": { title: "Open in preferred editor", sortWeight: 1 },
diff --git a/apps/web/src/routes/_chat.index.tsx b/apps/web/src/routes/_chat.index.tsx
index a90111e2af5..47b26ef4bb9 100644
--- a/apps/web/src/routes/_chat.index.tsx
+++ b/apps/web/src/routes/_chat.index.tsx
@@ -33,7 +33,7 @@ function HostedStaticOnboardingState() {
       <div className="flex min-h-0 min-w-0 flex-1 flex-col overflow-hidden bg-background">
         <header className="border-b border-border px-3 py-2 sm:px-5 sm:py-3">
           <div className="flex items-center gap-2">
-            <SidebarTrigger className="size-7 shrink-0 md:hidden" />
+            <SidebarTrigger className="size-7 shrink-0 group-data-[state=expanded]/sidebar-wrapper:md:hidden" />
             <span className="text-sm font-medium text-foreground md:text-muted-foreground/60">
               {APP_DISPLAY_NAME}
             </span>
diff --git a/apps/web/src/routes/_settings.diagnostics.tsx b/apps/web/src/routes/_settings.diagnostics.tsx
index d65a8281a84..9dd96b9b5a7 100644
--- a/apps/web/src/routes/_settings.diagnostics.tsx
+++ b/apps/web/src/routes/_settings.diagnostics.tsx
@@ -14,7 +14,7 @@ function DiagnosticsRouteView() {
     <SidebarInset className="h-dvh min-h-0 overflow-hidden overscroll-y-none bg-background text-foreground">
       <div className="flex min-h-0 min-w-0 flex-1 flex-col overflow-hidden bg-background">
         <header className="flex items-center gap-2 border-b border-border px-3 py-2 sm:px-5 sm:py-3">
-          <SidebarTrigger className="size-7 shrink-0 md:hidden" />
+          <SidebarTrigger className="size-7 shrink-0 group-data-[state=expanded]/sidebar-wrapper:md:hidden" />
           <Button
             size="xs"
             variant="ghost"
diff --git a/packages/contracts/src/keybindings.ts b/packages/contracts/src/keybindings.ts
index baebada1552..cba2326ef6f 100644
--- a/packages/contracts/src/keybindings.ts
+++ b/packages/contracts/src/keybindings.ts
@@ -57,6 +57,7 @@ const STATIC_KEYBINDING_COMMANDS = [
   "workspace.terminal",
   "diff.toggle",
   "commandPalette.toggle",
+  "sidebar.toggle",
   "chat.new",
   "chat.newLocal",
   "editor.openFavorite",
diff --git a/packages/shared/src/keybindings.ts b/packages/shared/src/keybindings.ts
index f77091482c8..ca86f0af8f3 100644
--- a/packages/shared/src/keybindings.ts
+++ b/packages/shared/src/keybindings.ts
@@ -28,6 +28,7 @@ export const DEFAULT_KEYBINDINGS: ReadonlyArray<KeybindingRule> = [
   { key: "ctrl+`", command: "workspace.terminal", when: "!terminalFocus" },
   { key: "mod+d", command: "diff.toggle", when: "!terminalFocus" },
   { key: "mod+k", command: "commandPalette.toggle", when: "!terminalFocus" },
+  { key: "mod+b", command: "sidebar.toggle", when: "!terminalFocus" },
   { key: "mod+n", command: "chat.new", when: "!terminalFocus" },
   { key: "mod+shift+o", command: "chat.new", when: "!terminalFocus" },
   { key: "mod+shift+n", command: "chat.newLocal", when: "!terminalFocus" },