diff --git a/webviews/src/agent-session/acpmux/App.tsx b/webviews/src/agent-session/acpmux/App.tsx
index 263e99b9e255..013b513e15cd 100644
--- a/webviews/src/agent-session/acpmux/App.tsx
+++ b/webviews/src/agent-session/acpmux/App.tsx
@@ -541,7 +541,7 @@ import { InboxNoticeCard } from "./conversation/InboxNoticeCard";
 import { mergeInboxNotices, type InboxMessage } from "./conversation/inboxNotice";
 import { configureNativeSidebarPreviewVariant, configureSidebarPreviewVariant } from "./sidebarPreview";
 import { cloudCredentialRecovery } from "./cloudCredentialRecovery";
-import { cloudAgentLogin } from "./cloudAgentLogin";
+import { cloudAgentLogin, localApiKeyLogin } from "./cloudAgentLogin";
 import { handoffTurns } from "./cloudHandoffTurn";
 import { configureTurnActionsPlacement } from "./turnActionsPlacement";
 import { archiveRow, markUnreadRow } from "./header/archiveRow";
@@ -7618,7 +7618,13 @@ function AcpmuxPane() {
       ),
       // A Cloud chat's agent signs in on its own machine (Leo 2026-11-01: "yes those are
       // important"): its own login, never this Mac's. Its page opens as a link click does here.
-      cloudSignIn: cloudAgentLogin({
+      // A chat here whose built-in Claude Code or Codex is not signed in offers Use an API key
+      // (Leo 2026-10-26: "if user picks a model they don't have api key, we offer them to add
+      // credits or add their own api key").
+      ...((login: Parameters<typeof cloudAgentLogin>[0]) => ({
+        cloudSignIn: cloudAgentLogin(login),
+        apiKeySignIn: localApiKeyLogin(login),
+      }))({
         connected,
         machineID: cloudMachineID,
         sessionId: snapshot.sessionId,
diff --git a/webviews/src/agent-session/acpmux/cloudAgentLogin.ts b/webviews/src/agent-session/acpmux/cloudAgentLogin.ts
index 1275ae51d8bf..6004c9e2ed1a 100644
--- a/webviews/src/agent-session/acpmux/cloudAgentLogin.ts
+++ b/webviews/src/agent-session/acpmux/cloudAgentLogin.ts
@@ -144,10 +144,8 @@ export class LoginStepError extends Error {
   }
 }
 
-/// The sign-in a Cloud chat's sign-in failure offers, or undefined where there is none: a chat
-/// not connected, not on a Cloud machine, not Claude or Codex, or on an acpmux that does not
-/// advertise `agent_login`.
-export function cloudAgentLogin(options: {
+/// What ``cloudAgentLogin`` and ``localApiKeyLogin`` take.
+type LoginOptions = {
   connected: boolean;
   machineID: string | undefined;
   sessionId: string | undefined;
@@ -157,11 +155,34 @@ export function cloudAgentLogin(options: {
   openURL: (url: string) => void;
   isCurrent: (sessionId: string) => boolean;
   currentClient: () => LoginClient | undefined;
-}): CloudSignIn | undefined {
-  const { connected, machineID, sessionId, harness, supported, gesture, openURL, isCurrent, currentClient } = options;
+};
+
+/// The sign-in a Cloud chat's sign-in failure offers, or undefined where there is none: a chat
+/// not connected, not on a Cloud machine, not Claude or Codex, or on an acpmux that does not
+/// advertise `agent_login`.
+export function cloudAgentLogin(options: LoginOptions): CloudSignIn | undefined {
+  return options.machineID ? agentLogin(options) : undefined;
+}
+
+/// Use an API key for a chat on this Mac whose built-in Claude Code or Codex is not signed in (Leo
+/// 2026-10-26: "if user picks a model they don't have api key, we offer them to add credits or add
+/// their own api key"). acpmux saves the key where the agent's own CLI reads it (Claude's
+/// `settings.json` `env.ANTHROPIC_API_KEY`, `codex login --with-api-key`) and restarts the chat on it.
+/// Only the built-in `claude` and `codex` harnesses: a route (`claude-cr`, `claude-sr`) sets its own
+/// key and endpoint, which a saved key would never reach. Undefined for a Cloud chat (its card is
+/// ``cloudAgentLogin``'s).
+export function localApiKeyLogin(options: LoginOptions): CloudSignIn | undefined {
+  const harness = options.harness?.split("/").pop();
+  if (options.machineID || (harness !== "claude" && harness !== "codex")) return undefined;
+  return agentLogin(options);
+}
+
+/// The agent's own login on the chat's machine, or undefined for a chat not connected, not Claude or
+/// Codex, or on an acpmux that does not advertise `agent_login`.
+function agentLogin(options: LoginOptions): CloudSignIn | undefined {
+  const { connected, sessionId, harness, supported, gesture, openURL, isCurrent, currentClient } = options;
   const agent = agentKey(harness?.split("/").pop());
-  if (!connected || !machineID || !sessionId || !supported || (agent !== "claude" && agent !== "codex"))
-    return undefined;
+  if (!connected || !sessionId || !supported || (agent !== "claude" && agent !== "codex")) return undefined;
   const client = () => {
     const current = currentClient();
     if (!current || !isCurrent(sessionId)) throw new LoginStepError("failed");
diff --git a/webviews/src/agent-session/acpmux/conversation/TurnRows.tsx b/webviews/src/agent-session/acpmux/conversation/TurnRows.tsx
index 7200195a7ad7..2415f3960568 100644
--- a/webviews/src/agent-session/acpmux/conversation/TurnRows.tsx
+++ b/webviews/src/agent-session/acpmux/conversation/TurnRows.tsx
@@ -275,6 +275,7 @@ export function TurnFooter({ row }: { row: AcpmuxRow }) {
     reauthenticate,
     transferCloudCredentials,
     cloudSignIn,
+    apiKeySignIn,
     resume,
     compact,
     route,
@@ -373,6 +374,7 @@ export function TurnFooter({ row }: { row: AcpmuxRow }) {
           compact={compact}
           reauthenticate={reauthenticate}
           cloudSignIn={cloudSignIn}
+          apiKeySignIn={apiKeySignIn}
           retryRowId={row.retryRowId}
           prompt={prompt}
           retry={failedRetry}
@@ -482,6 +484,7 @@ function TurnFailure({
   compact,
   reauthenticate,
   cloudSignIn,
+  apiKeySignIn,
   retryRowId,
   prompt,
   retry,
@@ -500,6 +503,9 @@ function TurnFailure({
   reauthenticate?: () => void;
   /// A Cloud chat's own sign-in on its machine (cloudAgentLogin.ts, CloudSignIn.tsx).
   cloudSignIn?: CloudSignInActions;
+  /// A chat here whose built-in Claude Code or Codex is not signed in: Use an API key
+  /// (cloudAgentLogin.ts `localApiKeyLogin`).
+  apiKeySignIn?: CloudSignInActions;
   /// The failed prompt's row and text, which the Cloud sign-in sends again once signed in.
   retryRowId?: string;
   prompt?: string;
@@ -557,6 +563,10 @@ function TurnFailure({
   // card keeps only Use an API key of the sign-in, never Sign in to Claude, which would dead-end.
   const teamMachine = isTeamMachineSignIn(kind, route);
   const cloudSignInLeads = recovery === "sign-in" && cloudSignIn !== undefined && !signInFirst && !teamMachine;
+  // A chat here whose built-in Claude Code or Codex is not signed in (Leo 2026-10-26: "if user picks a
+  // model they don't have api key, we offer them to add credits or add their own api key"): Use an API
+  // key follows Sign in again, outlined; the key goes where the agent's own CLI reads it.
+  const localKey = recovery === "sign-in" && cloudSignIn === undefined ? apiKeySignIn : undefined;
   // Continue or Retry is the way out, or the second one after Switch model for a key or proxy
   // failure, or after Sign in again; never for trust (errorRecovery.ts).
   const offersRetry = goOn !== undefined && (recovery !== "sign-in" || signInFirst);
@@ -646,6 +656,7 @@ function TurnFailure({
             {t("turn.signInAgain")}
           </button>
         )}
+        {localKey && <CloudSignIn signIn={localKey} rowId={retryRowId} prompt={prompt} keyOnly />}
         {offersRetry && (
           <button
             type="button"
diff --git a/webviews/src/agent-session/acpmux/conversation/turnActions.ts b/webviews/src/agent-session/acpmux/conversation/turnActions.ts
index ea5c86ceefa0..057c09669355 100644
--- a/webviews/src/agent-session/acpmux/conversation/turnActions.ts
+++ b/webviews/src/agent-session/acpmux/conversation/turnActions.ts
@@ -85,6 +85,9 @@ export type TurnActions = {
   /// A Cloud chat's agent signs in on its own machine (cloudAgentLogin.ts): its own login run there,
   /// or an API key saved there, never this Mac's login. Absent where acpmux lacks `agent_login`.
   cloudSignIn?: import("../cloudAgentLogin").CloudSignIn;
+  /// A chat on this Mac whose built-in Claude Code or Codex is not signed in: Use an API key saves
+  /// one where that agent reads it (cloudAgentLogin.ts `localApiKeyLogin`). Absent for a Cloud chat.
+  apiKeySignIn?: import("../cloudAgentLogin").CloudSignIn;
   /// Who serves this chat's turns, for failure copy (cx-w10a): the harness profile's display name and id.
   route?: import("../failureCopy").FailureRoute;
   /// Opens the model and harness picker (a failure's "Switch model" action).
diff --git a/webviews/test/cloud-signin-card.test.tsx b/webviews/test/cloud-signin-card.test.tsx
index bcddb8fb5fd4..008716ee4a4b 100644
--- a/webviews/test/cloud-signin-card.test.tsx
+++ b/webviews/test/cloud-signin-card.test.tsx
@@ -5,7 +5,12 @@
 // the person's click. These tests drive the card and its wire with a mocked client.
 import { afterAll, beforeEach, expect, test } from "bun:test";
 import { JSDOM, VirtualConsole } from "jsdom";
-import { cloudAgentLogin, loginFailure, signInURL } from "../src/agent-session/acpmux/cloudAgentLogin";
+import {
+  cloudAgentLogin,
+  localApiKeyLogin,
+  loginFailure,
+  signInURL,
+} from "../src/agent-session/acpmux/cloudAgentLogin";
 
 const dom = new JSDOM("<!doctype html><div id=root></div>", {
   url: "http://localhost/",
@@ -115,13 +120,19 @@ function mockClient(replies: Partial<Record<string, (...args: unknown[]) => unkn
 
 function signInFor(
   client: ReturnType<typeof mockClient>["client"],
-  options: { harness?: string; tickets?: (string | undefined)[]; opened?: string[]; supported?: boolean } = {},
+  options: {
+    harness?: string;
+    tickets?: (string | undefined)[];
+    opened?: string[];
+    supported?: boolean;
+    local?: boolean;
+  } = {},
 ) {
   const tickets = options.tickets ?? ["ticket-1", "ticket-2"];
   const intents: unknown[] = [];
-  const signIn = cloudAgentLogin({
+  const signIn = (options.local ? localApiKeyLogin : cloudAgentLogin)({
     connected: true,
-    machineID: "provider-vm-1",
+    machineID: options.local ? undefined : "provider-vm-1",
     sessionId: "chat-1",
     harness: options.harness ?? "claude",
     supported: options.supported ?? true,
@@ -522,3 +533,67 @@ test("a card that goes away cancels its login and sends nothing after", async ()
   await flush();
   expect(sent).toEqual([]);
 });
+
+// Leo 2026-10-26: "if user picks a model they don't have api key, we offer them to add credits or add
+// their own api key". A chat on this Mac whose built-in Claude Code or Codex is not signed in offers
+// Use an API key beside Sign in again; acpmux saves it where the agent's own CLI reads it.
+const localRoute = { name: "Claude Code", harness: "claude" };
+
+test("Use an API key is offered only for a connected built-in Claude or Codex chat on this Mac", () => {
+  const { client } = mockClient();
+  const base = {
+    connected: true,
+    machineID: undefined,
+    sessionId: "chat-1",
+    harness: "claude",
+    supported: true,
+    gesture: async () => undefined,
+    openURL: () => undefined,
+    isCurrent: () => true,
+    currentClient: () => client as never,
+  };
+  expect(localApiKeyLogin(base)?.agent).toBe("claude");
+  expect(localApiKeyLogin({ ...base, harness: "codex" })?.agent).toBe("codex");
+  // A route sets its own key and endpoint: a saved key would never reach it.
+  expect(localApiKeyLogin({ ...base, harness: "claude-cr" })).toBeUndefined();
+  expect(localApiKeyLogin({ ...base, harness: "opencode" })).toBeUndefined();
+  // A Cloud chat's card is cloudAgentLogin's.
+  expect(localApiKeyLogin({ ...base, machineID: "vm" })).toBeUndefined();
+  expect(localApiKeyLogin({ ...base, connected: false })).toBeUndefined();
+  expect(localApiKeyLogin({ ...base, supported: false })).toBeUndefined();
+});
+
+test("a signed-out chat here offers Sign in again, then Use an API key, which saves and sends again", async () => {
+  const { client, calls, sent } = mockClient({ apiKey: () => ({ saved: true, restarted: true }) });
+  const { signIn, intents } = signInFor(client, { local: true });
+  await render({
+    route: localRoute,
+    apiKeySignIn: signIn,
+    reauthenticate: () => undefined,
+    switchModel: () => undefined,
+  });
+  expect(labels().slice(0, 2)).toEqual(["Sign in again", "Use an API key"]);
+  expect(button("Sign in again")!.classList.contains("cv-turn-error__primary")).toBe(true);
+  expect(button("Use an API key")!.classList.contains("cv-turn-error__primary")).toBe(false);
+  expect(button("Sign in to Claude")).toBeUndefined();
+  await act(async () => button("Use an API key")!.click());
+  const input = host.querySelector<HTMLInputElement>(".cv-turn-signin__input")!;
+  expect(input.type).toBe("password");
+  await typeInto(input, "sk-ant-local-key");
+  await act(async () => button("Save")!.click());
+  await flush();
+  expect(calls).toContainEqual(["apiKey", "claude", "chat-1", "sk-ant-local-key"]);
+  expect(host.innerHTML).not.toContain("sk-ant-local-key");
+  await act(async () => button("Send again")!.click());
+  await flush();
+  await flush();
+  expect(intents).toHaveLength(1);
+  expect(sent).toHaveLength(1);
+});
+
+test("no Use an API key here on a failure that is not a sign-in", async () => {
+  const { client } = mockClient();
+  const { signIn } = signInFor(client, { local: true });
+  await render({ route: localRoute, apiKeySignIn: signIn, retry: () => undefined }, "API Error: 529 overloaded_error");
+  expect(button("Use an API key")).toBeUndefined();
+});