diff --git a/.pi/extensions/pi-web.ts b/.pi/extensions/pi-web.ts
index 65111812..b2ccd2db 100644
--- a/.pi/extensions/pi-web.ts
+++ b/.pi/extensions/pi-web.ts
@@ -798,6 +798,8 @@ async function showRemoteAccess(
 export default function (pi: ExtensionAPI) {
   let lastAutoTitle: string | null = null;
 
+  let titleJobId = 0;
+
   pi.registerTool({
     name: "pi_web_set_tab_title",
     label: "Set Tab Title",
@@ -812,15 +814,49 @@ export default function (pi: ExtensionAPI) {
       title: Type.String({ description: "Short 2-5 word session title." }),
     }),
     async execute(_toolCallId, params, _signal, _onUpdate, ctx) {
-      const title = setPiWebTabTitle(pi, ctx, String(params.title ?? ""));
-      lastAutoTitle = title;
+      const title = String(params.title ?? "");
+      const backgroundTitleUpdates =
+        process.env["PI_WEB_BACKGROUND_TAB_TITLE"] === "1";
+
+      if (!backgroundTitleUpdates) {
+        const finalTitle = setPiWebTabTitle(pi, ctx, title);
+        lastAutoTitle = finalTitle;
+        return {
+          content: [{ type: "text", text: `Session title set to ${finalTitle}.` }],
+          details: { title: finalTitle },
+        };
+      }
+
+      const jobId = ++titleJobId;
+      const sessionFile = ctx.sessionManager.getSessionFile();
+
+      void (async () => {
+        try {
+          if (jobId !== titleJobId) return;
+          if (ctx.sessionManager.getSessionFile() !== sessionFile) return;
+
+          const finalTitle = setPiWebTabTitle(pi, ctx, title);
+          lastAutoTitle = finalTitle;
+          if (ctx.hasUI) {
+            ctx.ui.notify(`Session title set to ${finalTitle}.`, "info");
+          }
+        } catch (error) {
+          console.warn("[pi-web] background tab title update failed", error);
+        }
+      })();
+
       return {
-        content: [{ type: "text", text: `Session title set to ${title}.` }],
-        details: { title },
+        content: [{ type: "text", text: "Session title update queued." }],
+        details: { queued: true, title },
       };
     },
   });
 
+  pi.on("session_shutdown", () => {
+    // Cancel any queued background title update before reload/session replacement.
+    titleJobId++;
+  });
+
   pi.on("input", async (event, ctx) => {
     const title =
       typeof event.text === "string" ? deriveTitleFromInput(event.text) : null;
diff --git a/README.md b/README.md
index f534683f..31a9d766 100644
--- a/README.md
+++ b/README.md
@@ -62,7 +62,7 @@ After `pi install npm:@ygncode/pi-web`, you get:
 | `/pi-web` | Show status, version, start/stop/restart the server, or update |
 | `/remote` | Show a QR code and URL for remote access over Tailscale |
 | `/refresh` | Pull new messages written from remote browsers back into the terminal session |
-| `set_tab_title` | Tool that updates the session title; also auto‑derives a short title from each user message |
+| `set_tab_title` | Tool that updates the session title; also auto‑derives a short title from each user message. Set `PI_WEB_BACKGROUND_TAB_TITLE=1` to queue title updates in the background. |
 
 The package also installs the pi-web binary to `~/.pi/agent/bin/pi-web` and sets up auto-start on login.
 
@@ -81,7 +81,7 @@ To set a token for remote access, create `~/.config/pi-web/env`:
 PI_WEB_TOKEN=your-token-here
 ```
 
-For more details (manual setup, custom ports, non-loopback binds), see [docs/install.md](docs/install.md).
+For more details (manual setup, custom ports, non-loopback binds, optional extension settings), see [docs/install.md](docs/install.md).
 
 ## Development
 
diff --git a/docs/install.md b/docs/install.md
index e6a51807..14834b5d 100644
--- a/docs/install.md
+++ b/docs/install.md
@@ -129,6 +129,15 @@ PI_WEB_TOKEN=$(openssl rand -hex 16) pi-web --host 192.168.1.50
 
 By default, pi-web binds to `127.0.0.1`. If Tailscale is running with MagicDNS, pi-web also runs `tailscale serve --bg --https=<port> http://127.0.0.1:<port>` and prints the HTTPS tailnet URL. Any explicit non-loopback bind requires `PI_WEB_TOKEN` to be set; pass `--insecure` to override for local testing.
 
+## Optional Environment Settings
+
+Optional extension settings can be added to `~/.config/pi-web/env`:
+
+```bash
+# Queue tab title updates in the background instead of blocking the agent turn.
+PI_WEB_BACKGROUND_TAB_TITLE=1
+```
+
 ## Remote Access
 
 Leave pi-web listening locally, then use the printed Tailscale HTTPS URL from your phone or laptop on the tailnet.
diff --git a/tests/extensions/pi-web.test.ts b/tests/extensions/pi-web.test.ts
index d62b087d..0c8c36fb 100644
--- a/tests/extensions/pi-web.test.ts
+++ b/tests/extensions/pi-web.test.ts
@@ -36,7 +36,7 @@ vi.mock('node:fs', async (importOriginal) => {
   };
 });
 
-import {
+import piWebExtension, {
   isTailscaleHost,
   isSSH,
   normalizeCommandArgs,
@@ -54,6 +54,37 @@ declare global {
   var __MOCK_PI_WEB_ENV_CONTENT__: string | undefined;
 }
 
+function createExtensionHarness() {
+  const tools = new Map<string, any>();
+  const handlers = new Map<string, Function[]>();
+  const pi = {
+    registerTool: vi.fn((tool: any) => tools.set(tool.name, tool)),
+    registerCommand: vi.fn(),
+    on: vi.fn((event: string, handler: Function) => {
+      const list = handlers.get(event) ?? [];
+      list.push(handler);
+      handlers.set(event, list);
+    }),
+    setSessionName: vi.fn(),
+    exec: vi.fn(),
+  };
+
+  piWebExtension(pi as any);
+
+  const ctx = {
+    hasUI: true,
+    ui: {
+      setTitle: vi.fn(),
+      notify: vi.fn(),
+    },
+    sessionManager: {
+      getSessionFile: vi.fn(() => '/tmp/pi-session.jsonl'),
+    },
+  };
+
+  return { pi, ctx, tools, handlers };
+}
+
 // ── isSSH ───────────────────────────────────────────────────────────
 describe('isSSH', () => {
   const orig = { ...process.env };
@@ -212,6 +243,65 @@ describe('deriveTitleFromInput', () => {
   });
 });
 
+// ── pi_web_set_tab_title tool ───────────────────────────────────────
+describe('pi_web_set_tab_title tool', () => {
+  const orig = { ...process.env };
+
+  afterEach(() => {
+    process.env = { ...orig };
+    vi.restoreAllMocks();
+  });
+
+  it('keeps the default synchronous response shape', async () => {
+    delete process.env.PI_WEB_BACKGROUND_TAB_TITLE;
+    const { pi, ctx, tools } = createExtensionHarness();
+    const tool = tools.get('pi_web_set_tab_title');
+
+    expect(tool).toBeDefined();
+    const result = await tool.execute(
+      'call-1',
+      { title: ' Test Session ' },
+      undefined,
+      undefined,
+      ctx,
+    );
+
+    expect(ctx.ui.setTitle).toHaveBeenCalledWith('Test Session');
+    expect(pi.setSessionName).toHaveBeenCalledWith('Test Session');
+    expect(ctx.ui.notify).not.toHaveBeenCalled();
+    expect(result).toEqual({
+      content: [{ type: 'text', text: 'Session title set to Test Session.' }],
+      details: { title: 'Test Session' },
+    });
+  });
+
+  it('queues title updates when PI_WEB_BACKGROUND_TAB_TITLE is set', async () => {
+    process.env.PI_WEB_BACKGROUND_TAB_TITLE = '1';
+    const { pi, ctx, tools } = createExtensionHarness();
+    const tool = tools.get('pi_web_set_tab_title');
+
+    expect(tool).toBeDefined();
+    const result = await tool.execute(
+      'call-1',
+      { title: 'Background Session' },
+      undefined,
+      undefined,
+      ctx,
+    );
+
+    expect(ctx.ui.setTitle).toHaveBeenCalledWith('Background Session');
+    expect(pi.setSessionName).toHaveBeenCalledWith('Background Session');
+    expect(ctx.ui.notify).toHaveBeenCalledWith(
+      'Session title set to Background Session.',
+      'info',
+    );
+    expect(result).toEqual({
+      content: [{ type: 'text', text: 'Session title update queued.' }],
+      details: { queued: true, title: 'Background Session' },
+    });
+  });
+});
+
 // ── withToken / readPiWebToken ──────────────────────────────────────
 describe('token helpers', () => {
   beforeEach(() => {