diff --git a/extensions/codex/src/client.test.ts b/extensions/codex/src/client.test.ts
new file mode 100644
index 0000000..1572cef
--- /dev/null
+++ b/extensions/codex/src/client.test.ts
@@ -0,0 +1,336 @@
+import type { Api, AuthResult, Model } from "@earendil-works/pi-ai";
+import { afterEach, expect, it, vi } from "vitest";
+import { fetchCodexUsage, type CodexAccountRegistry } from "./client.ts";
+
+const BASE_URL = "https://chatgpt.com/backend-api";
+const model: Model<Api> = {
+  id: "gpt-6-sol",
+  name: "Sol",
+  provider: "openai-codex",
+  api: "openai-codex-responses",
+  baseUrl: BASE_URL,
+  reasoning: true,
+  input: ["text"],
+  cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+  contextWindow: 272_000,
+  maxTokens: 128_000,
+};
+
+function token(account = "test-account"): string {
+  const payload = { "https://api.openai.com/auth": { chatgpt_account_id: account } };
+  return `e30.${Buffer.from(JSON.stringify(payload)).toString("base64url")}.fake-signature`;
+}
+
+function json(value: unknown): Response {
+  return new Response(JSON.stringify(value), { headers: { "Content-Type": "application/json" } });
+}
+
+function deferred<T>() {
+  let resolve!: (value: T) => void;
+  const promise = new Promise<T>((done) => {
+    resolve = done;
+  });
+  return { promise, resolve };
+}
+
+function fixture() {
+  const auth: AuthResult = { source: "OAuth", auth: { apiKey: token() } };
+  const provider = { baseUrl: BASE_URL, getModels: () => [model] };
+  const registry = {
+    getProvider: vi.fn<CodexAccountRegistry["getProvider"]>(() => provider),
+    getProviderAuth: vi.fn<CodexAccountRegistry["getProviderAuth"]>(async () => auth),
+    isUsingOAuth: vi.fn<CodexAccountRegistry["isUsingOAuth"]>(() => true),
+  };
+  const fetcher = vi.fn<typeof fetch>(async () => json({ plan_type: "plus" }));
+  return { registry, provider, auth, fetcher };
+}
+
+afterEach(() => {
+  vi.useRealTimers();
+});
+
+it("uses Pi's existing Codex auth for the fixed account endpoint", async () => {
+  const f = fixture();
+  f.auth.auth.headers = { "X-Unrelated-Secret": "must-not-forward" };
+  expect(await fetchCodexUsage(f.registry, undefined, f.fetcher)).toEqual({ plan_type: "plus" });
+  expect(f.registry.getProviderAuth).toHaveBeenCalledExactlyOnceWith("openai-codex");
+  expect(f.fetcher).toHaveBeenCalledExactlyOnceWith(
+    `${BASE_URL}/wham/usage`,
+    expect.objectContaining({ method: "GET", redirect: "error", signal: expect.any(AbortSignal) }),
+  );
+  const headers = new Headers(f.fetcher.mock.calls[0][1]?.headers);
+  expect(Object.fromEntries(headers)).toEqual({
+    accept: "application/json",
+    authorization: `Bearer ${f.auth.auth.apiKey}`,
+    "chatgpt-account-id": "test-account",
+  });
+});
+
+it("derives the account from the token like Pi's legacy Codex transport", async () => {
+  const f = fixture();
+  f.auth.auth.headers = { "ChatGPT-Account-Id": "selected-account" };
+  await fetchCodexUsage(f.registry, undefined, f.fetcher);
+  const headers = new Headers(f.fetcher.mock.calls[0][1]?.headers);
+  expect(headers.get("chatgpt-account-id")).toBe("test-account");
+});
+
+it("resolves auth afresh rather than retaining another account's credentials", async () => {
+  const f = fixture();
+  f.registry.getProviderAuth
+    .mockResolvedValueOnce({ source: "OAuth", auth: { apiKey: token("first") } })
+    .mockResolvedValueOnce({ source: "OAuth", auth: { apiKey: token("second") } });
+  await fetchCodexUsage(f.registry, undefined, f.fetcher);
+  await fetchCodexUsage(f.registry, undefined, f.fetcher);
+  const accounts = f.fetcher.mock.calls.map(([, init]) =>
+    new Headers(init?.headers).get("chatgpt-account-id"),
+  );
+  expect(accounts).toEqual(["first", "second"]);
+});
+
+it.each(["provider endpoint", "model endpoint", "auth endpoint"] as const)(
+  "does not send credentials for an unsupported %s configuration",
+  async (configuration) => {
+    const f = fixture();
+    if (configuration === "provider endpoint") f.provider.baseUrl = "https://gateway.invalid";
+    if (configuration === "model endpoint") {
+      f.provider.getModels = () => [{ ...model, baseUrl: "https://gateway.invalid" }];
+    }
+    if (configuration === "auth endpoint") f.auth.auth.baseUrl = "https://gateway.invalid";
+    await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+      code: "unsupported",
+    });
+    expect(f.fetcher).not.toHaveBeenCalled();
+  },
+);
+
+it("requires Pi's Codex OAuth login rather than API-key authentication", async () => {
+  const f = fixture();
+  f.registry.isUsingOAuth.mockReturnValue(false);
+  await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "auth",
+  });
+  expect(f.fetcher).not.toHaveBeenCalled();
+});
+
+it.each([
+  { label: "opaque", key: "opaque-api-key" },
+  { label: "token-shaped", key: token() },
+])("rejects resolved $label API keys even if Pi's OAuth snapshot is stale", async ({ key }) => {
+  const f = fixture();
+  f.auth.source = "models.json";
+  f.auth.auth.apiKey = key;
+  f.auth.auth.headers = { "ChatGPT-Account-Id": "stale-account" };
+  await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "auth",
+  });
+  expect(f.fetcher).not.toHaveBeenCalled();
+});
+
+it("rechecks the endpoint after Pi finishes resolving credentials", async () => {
+  const f = fixture();
+  const auth = deferred<AuthResult>();
+  f.registry.getProviderAuth.mockReturnValue(auth.promise);
+  const request = fetchCodexUsage(f.registry, undefined, f.fetcher);
+  f.provider.baseUrl = "https://gateway.invalid";
+  auth.resolve(f.auth);
+  await expect(request).rejects.toMatchObject({ code: "unsupported" });
+  expect(f.fetcher).not.toHaveBeenCalled();
+});
+
+it("does not fetch or expose Pi's raw authentication errors", async () => {
+  const f = fixture();
+  f.registry.getProviderAuth.mockRejectedValue(new Error("private token refresh details"));
+  await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "auth",
+    message: "Codex account access is unavailable. Check your Pi Codex login.",
+  });
+  expect(f.fetcher).not.toHaveBeenCalled();
+});
+
+it.each([
+  undefined,
+  { source: "OAuth", auth: {} },
+  { source: "OAuth", auth: { apiKey: "not-a-codex-token" } },
+])("rejects missing or unusable auth without a request: %j", async (auth) => {
+  const f = fixture();
+  f.registry.getProviderAuth.mockResolvedValue(auth);
+  await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "auth",
+  });
+  expect(f.fetcher).not.toHaveBeenCalled();
+});
+
+it("does not expose transport error details", async () => {
+  const f = fixture();
+  f.fetcher.mockRejectedValue(new Error("Authorization: Bearer secret"));
+  await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "network",
+    message: "Could not reach the Codex account service.",
+  });
+});
+
+it.each([401, 403])("reports HTTP %s without exposing the server's error body", async (status) => {
+  const f = fixture();
+  const cancel = vi.fn();
+  const body = new ReadableStream<Uint8Array>({ cancel });
+  f.fetcher.mockResolvedValue(new Response(body, { status }));
+  await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "auth",
+    message: "Codex account access is unavailable. Check your Pi Codex login.",
+  });
+  expect(cancel).toHaveBeenCalledOnce();
+});
+
+it("returns retry-after information without automatically retrying", async () => {
+  const f = fixture();
+  f.fetcher.mockResolvedValue(
+    new Response("private error", { status: 429, headers: { "Retry-After": "60" } }),
+  );
+  await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "http",
+    message: "Codex account service is rate limited.",
+    retryAfterMs: 60_000,
+  });
+  expect(f.fetcher).toHaveBeenCalledOnce();
+});
+
+it("does not follow or display a redirected endpoint", async () => {
+  const f = fixture();
+  f.fetcher.mockResolvedValue(
+    new Response(null, { status: 302, headers: { Location: "https://other.invalid/private" } }),
+  );
+  await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "http",
+    message: "Codex account request failed (HTTP 302).",
+  });
+  expect(f.fetcher.mock.calls[0][1]?.redirect).toBe("error");
+  expect(f.fetcher).toHaveBeenCalledOnce();
+});
+
+it("cancels a chunked response before retaining more than the byte limit", async () => {
+  const f = fixture();
+  const cancel = vi.fn();
+  const body = new ReadableStream<Uint8Array>({
+    start(controller) {
+      controller.enqueue(new Uint8Array(1024 * 1024));
+      controller.enqueue(new Uint8Array(1));
+    },
+    cancel,
+  });
+  f.fetcher.mockResolvedValue(new Response(body));
+  await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "response",
+    message: "Codex account response was too large.",
+  });
+  expect(cancel).toHaveBeenCalledOnce();
+});
+
+it("reports invalid JSON without repeating returned content", async () => {
+  const f = fixture();
+  f.fetcher.mockResolvedValue(new Response("<html>private server details</html>"));
+  await expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "response",
+    message: "Codex account service returned invalid JSON.",
+  });
+});
+
+it("cancels during handoff of an already-buffered response", async () => {
+  const f = fixture();
+  const started = deferred<void>();
+  const incoming = deferred<Response>();
+  const controller = new AbortController();
+  const response = json({ plan_type: "plus" });
+  const discard = vi.spyOn(response.body!, "cancel");
+  f.fetcher.mockImplementation(() => {
+    started.resolve();
+    return incoming.promise;
+  });
+  const request = fetchCodexUsage(f.registry, controller.signal, f.fetcher);
+  await started.promise;
+  incoming.resolve(response);
+  queueMicrotask(() => controller.abort());
+  await expect(request).rejects.toMatchObject({ code: "cancelled" });
+  expect(discard).toHaveBeenCalledOnce();
+});
+
+it("cancels before auth resolution if the caller is already aborted", async () => {
+  const f = fixture();
+  const controller = new AbortController();
+  controller.abort();
+  await expect(fetchCodexUsage(f.registry, controller.signal, f.fetcher)).rejects.toMatchObject({
+    code: "cancelled",
+  });
+  expect(f.registry.getProviderAuth).not.toHaveBeenCalled();
+  expect(f.fetcher).not.toHaveBeenCalled();
+});
+
+it("ignores auth that resolves after the caller cancels", async () => {
+  const f = fixture();
+  const auth = deferred<AuthResult>();
+  f.registry.getProviderAuth.mockReturnValue(auth.promise);
+  const controller = new AbortController();
+  const request = fetchCodexUsage(f.registry, controller.signal, f.fetcher);
+  controller.abort();
+  await expect(request).rejects.toMatchObject({ code: "cancelled" });
+  auth.resolve(f.auth);
+  await auth.promise;
+  expect(f.fetcher).not.toHaveBeenCalled();
+});
+
+it("discards a response arriving after cancellation even if fetch ignores the signal", async () => {
+  const f = fixture();
+  const started = deferred<void>();
+  const response = deferred<Response>();
+  const discarded = deferred<void>();
+  f.fetcher.mockImplementation(() => {
+    started.resolve();
+    return response.promise;
+  });
+  const controller = new AbortController();
+  const request = fetchCodexUsage(f.registry, controller.signal, f.fetcher);
+  await started.promise;
+  controller.abort();
+  await expect(request).rejects.toMatchObject({ code: "cancelled" });
+  response.resolve(new Response(new ReadableStream({ cancel: () => discarded.resolve() })));
+  await discarded.promise;
+});
+
+it("bounds the wait for Pi's refresh without taking over refresh cancellation", async () => {
+  vi.useFakeTimers();
+  const f = fixture();
+  f.registry.getProviderAuth.mockReturnValue(new Promise(() => {}));
+  const result = expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "timeout",
+  });
+  await vi.advanceTimersByTimeAsync(10_000);
+  await result;
+  expect(f.fetcher).not.toHaveBeenCalled();
+  expect(vi.getTimerCount()).toBe(0);
+});
+
+it("bounds the wait for response headers", async () => {
+  vi.useFakeTimers();
+  const f = fixture();
+  f.fetcher.mockReturnValue(new Promise(() => {}));
+  const result = expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "timeout",
+  });
+  await vi.advanceTimersByTimeAsync(10_000);
+  await result;
+  expect(f.fetcher).toHaveBeenCalledOnce();
+  expect(vi.getTimerCount()).toBe(0);
+});
+
+it("keeps the deadline active while consuming the response body", async () => {
+  vi.useFakeTimers();
+  const f = fixture();
+  const cancel = vi.fn();
+  f.fetcher.mockResolvedValue(new Response(new ReadableStream<Uint8Array>({ cancel })));
+  const result = expect(fetchCodexUsage(f.registry, undefined, f.fetcher)).rejects.toMatchObject({
+    code: "timeout",
+  });
+  await vi.advanceTimersByTimeAsync(10_000);
+  await result;
+  expect(cancel).toHaveBeenCalledOnce();
+  expect(vi.getTimerCount()).toBe(0);
+});
diff --git a/extensions/codex/src/client.ts b/extensions/codex/src/client.ts
new file mode 100644
index 0000000..172471f
--- /dev/null
+++ b/extensions/codex/src/client.ts
@@ -0,0 +1,250 @@
+import type { AuthResult, Provider } from "@earendil-works/pi-ai";
+import type { ExtensionContext } from "@earendil-works/pi-coding-agent";
+
+const PROVIDER = "openai-codex";
+const BASE_URL = "https://chatgpt.com/backend-api";
+const USAGE_URL = `${BASE_URL}/wham/usage`;
+const TIMEOUT_MS = 10_000;
+const MAX_RESPONSE_BYTES = 1024 * 1024;
+
+export type CodexAccountRegistry = Pick<
+  ExtensionContext["modelRegistry"],
+  "getProviderAuth" | "isUsingOAuth"
+> & {
+  getProvider(id: string): Pick<Provider, "baseUrl" | "getModels"> | undefined;
+};
+
+type Failure = "auth" | "unsupported" | "cancelled" | "timeout" | "network" | "response" | "http";
+
+export class CodexAccountError extends Error {
+  constructor(
+    readonly code: Failure,
+    message: string,
+    readonly retryAfterMs?: number,
+  ) {
+    super(message);
+    this.name = "CodexAccountError";
+  }
+}
+
+/** Read account data with Pi's existing login. Pi owns credential refresh and persistence. */
+export async function fetchCodexUsage(
+  registry: CodexAccountRegistry,
+  signal?: AbortSignal,
+  fetcher: typeof fetch = fetch,
+): Promise<unknown> {
+  const deadline = new AbortController();
+  const timer = setTimeout(() => deadline.abort(), TIMEOUT_MS);
+  const requestSignal = signal ? AbortSignal.any([signal, deadline.signal]) : deadline.signal;
+  try {
+    requestSignal.throwIfAborted();
+    const headers = await resolveAccountHeaders(registry, requestSignal);
+    requestSignal.throwIfAborted();
+    const data = await requestUsage(headers, requestSignal, fetcher);
+    requestSignal.throwIfAborted();
+    return data;
+  } catch (error) {
+    if (signal?.aborted)
+      throw new CodexAccountError("cancelled", "Codex account request cancelled.");
+    if (deadline.signal.aborted)
+      throw new CodexAccountError("timeout", "Codex account request timed out.");
+    if (error instanceof CodexAccountError) throw error;
+    // Neither auth errors nor fetch errors are safe to display verbatim.
+    throw new CodexAccountError("network", "Could not reach the Codex account service.");
+  } finally {
+    clearTimeout(timer);
+    deadline.abort();
+  }
+}
+
+async function resolveAccountHeaders(
+  registry: CodexAccountRegistry,
+  signal: AbortSignal,
+): Promise<Headers> {
+  const provider = registry.getProvider(PROVIDER);
+  const model = provider
+    ?.getModels()
+    .find(
+      (candidate) =>
+        candidate.provider === PROVIDER &&
+        candidate.api === "openai-codex-responses" &&
+        officialBase(candidate.baseUrl),
+    );
+  if (!officialBase(provider?.baseUrl) || !model) {
+    throw new CodexAccountError(
+      "unsupported",
+      "Account usage requires the official Codex provider.",
+    );
+  }
+  if (!registry.isUsingOAuth(model)) throw authError();
+
+  let resolvedAuth: AuthResult | undefined;
+  try {
+    // Pi owns token refresh; aborting here only stops our wait for its result.
+    resolvedAuth = await waitWithAbort(registry.getProviderAuth(PROVIDER), signal);
+  } catch {
+    throw authError();
+  }
+  signal.throwIfAborted();
+  // Pi's resolved source describes these credentials, unlike its availability snapshot.
+  if (!resolvedAuth || resolvedAuth.source !== "OAuth") throw authError();
+  if (
+    !officialBase(registry.getProvider(PROVIDER)?.baseUrl) ||
+    (resolvedAuth.auth.baseUrl !== undefined && !officialBase(resolvedAuth.auth.baseUrl))
+  ) {
+    throw new CodexAccountError(
+      "unsupported",
+      "Account usage does not support endpoint overrides.",
+    );
+  }
+  const accessToken = resolvedAuth.auth.apiKey;
+  if (!accessToken) throw authError();
+  // Match Pi's legacy transport: token routing overrides configured account headers.
+  const accountId = tokenAccountId(accessToken);
+  if (!accountId) throw authError();
+  try {
+    // Forward only the two credentials needed by this fixed endpoint, never
+    // arbitrary provider headers or provider-scoped environment values.
+    return new Headers({
+      Accept: "application/json",
+      Authorization: `Bearer ${accessToken}`,
+      "ChatGPT-Account-Id": accountId,
+    });
+  } catch {
+    throw authError();
+  }
+}
+
+function officialBase(url: string | undefined): boolean {
+  return url?.replace(/\/+$/, "") === BASE_URL;
+}
+
+function tokenAccountId(token: string): string | undefined {
+  try {
+    const parts = token.split(".");
+    if (parts.length !== 3) return undefined;
+    // Routing metadata only, not signature verification. Legacy Pi Codex auth
+    // returns the access token without the account header its transport derives.
+    const payload: unknown = JSON.parse(Buffer.from(parts[1], "base64url").toString("utf8"));
+    if (!payload || typeof payload !== "object" || !("https://api.openai.com/auth" in payload))
+      return undefined;
+    const claim = payload["https://api.openai.com/auth"];
+    if (!claim || typeof claim !== "object" || !("chatgpt_account_id" in claim)) return undefined;
+    const accountId = claim.chatgpt_account_id;
+    if (typeof accountId !== "string" || !accountId.trim()) return undefined;
+    return accountId;
+  } catch {
+    return undefined;
+  }
+}
+
+function authError(): CodexAccountError {
+  return new CodexAccountError(
+    "auth",
+    "Codex account access is unavailable. Check your Pi Codex login.",
+  );
+}
+
+async function requestUsage(
+  headers: Headers,
+  requestSignal: AbortSignal,
+  fetcher: typeof fetch,
+): Promise<unknown> {
+  let receivedResponse: Response | undefined;
+  try {
+    const request = fetcher(USAGE_URL, {
+      method: "GET",
+      headers,
+      redirect: "error",
+      signal: requestSignal,
+    }).then((response) => {
+      receivedResponse = response;
+      // Fetch adapters can ignore abort and deliver a response after we stopped waiting.
+      if (requestSignal.aborted) {
+        discardBody(response);
+        requestSignal.throwIfAborted();
+      }
+      return response;
+    });
+    const response = await waitWithAbort(request, requestSignal);
+    if (!response.ok) throw responseError(response);
+    return await readJson(response, requestSignal);
+  } finally {
+    if (receivedResponse && !receivedResponse.bodyUsed) discardBody(receivedResponse);
+  }
+}
+
+function responseError(response: Response): CodexAccountError {
+  if (response.status === 401 || response.status === 403) return authError();
+  if (response.status === 429) {
+    const header = response.headers.get("retry-after");
+    let retryAfterMs: number | undefined;
+    if (header) {
+      const seconds = Number(header);
+      const delay = Number.isFinite(seconds) ? seconds * 1000 : Date.parse(header) - Date.now();
+      if (Number.isFinite(delay) && delay >= 0) retryAfterMs = delay;
+    }
+    return new CodexAccountError("http", "Codex account service is rate limited.", retryAfterMs);
+  }
+  return new CodexAccountError("http", `Codex account request failed (HTTP ${response.status}).`);
+}
+
+function discardBody(response: Response): void {
+  void response.body?.cancel().catch(() => {});
+}
+
+async function readJson(response: Response, signal: AbortSignal): Promise<unknown> {
+  const bytes = await readResponseBytes(response, signal);
+  signal.throwIfAborted();
+  try {
+    const text = new TextDecoder("utf-8", { fatal: true }).decode(bytes);
+    return JSON.parse(text);
+  } catch {
+    throw new CodexAccountError("response", "Codex account service returned invalid JSON.");
+  }
+}
+
+async function readResponseBytes(response: Response, signal: AbortSignal): Promise<Uint8Array> {
+  if (!response.body) throw new CodexAccountError("response", "Codex account response was empty.");
+  const reader = response.body.getReader();
+  const bytes = new Uint8Array(MAX_RESPONSE_BYTES);
+  let bytesRead = 0;
+  let fullyRead = false;
+  try {
+    for (;;) {
+      const { value, done } = await waitWithAbort(reader.read(), signal);
+      if (done) {
+        fullyRead = true;
+        return bytes.subarray(0, bytesRead);
+      }
+      if (value.byteLength > bytes.byteLength - bytesRead) {
+        throw new CodexAccountError("response", "Codex account response was too large.");
+      }
+      bytes.set(value, bytesRead);
+      bytesRead += value.byteLength;
+    }
+  } finally {
+    if (!fullyRead) void reader.cancel().catch(() => {});
+    reader.releaseLock();
+  }
+}
+
+async function waitWithAbort<T>(promise: Promise<T>, signal: AbortSignal): Promise<T> {
+  if (signal.aborted) {
+    // The operation has already started; observe a late rejection without accepting its result.
+    void promise.catch(() => {});
+    signal.throwIfAborted();
+  }
+  let abort = () => {};
+  const cancelled = new Promise<never>((_resolve, reject) => {
+    abort = () => reject(signal.reason);
+    signal.addEventListener("abort", abort, { once: true });
+  });
+  try {
+    const value = await Promise.race([promise, cancelled]);
+    signal.throwIfAborted();
+    return value;
+  } finally {
+    signal.removeEventListener("abort", abort);
+  }
+}
diff --git a/extensions/codex/src/index.test.ts b/extensions/codex/src/index.test.ts
index d377de2..bd06bae 100644
--- a/extensions/codex/src/index.test.ts
+++ b/extensions/codex/src/index.test.ts
@@ -3,6 +3,12 @@ import { join } from "node:path";
 import type { ExtensionAPI, ExtensionCommandContext } from "@earendil-works/pi-coding-agent";
 import { afterAll, expect, it, vi } from "vitest";
 import codex from "./index.ts";
+import { fetchCodexUsage } from "./client.ts";
+
+vi.mock("./client.ts", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("./client.ts")>()),
+  fetchCodexUsage: vi.fn(),
+}));
 
 const directory = await vi.hoisted(async () => {
   const { mkdtempSync } = await import("node:fs");
@@ -21,6 +27,7 @@ afterAll(() => {
 });
 
 async function load(prefix = "eleith") {
+  vi.mocked(fetchCodexUsage).mockReset();
   writeFileSync(configPath, JSON.stringify({ commandPrefix: prefix }));
   type Command = Parameters<ExtensionAPI["registerCommand"]>[1];
   type Listener = (
@@ -49,6 +56,7 @@ async function load(prefix = "eleith") {
     hasUI: false,
     isIdle: () => true,
     getContextUsage: () => undefined,
+    modelRegistry: {},
     ui: { notify, confirm: vi.fn(async () => false) },
     sessionManager: { getBranch: () => [], getSessionId: () => "session", getLeafId: () => null },
   } as unknown as ExtensionCommandContext;
@@ -82,6 +90,7 @@ it("registers only the configured native command once after binding", async () =
   expect(await context.command().getArgumentCompletions?.("")).toEqual([
     { value: "extend", label: "extend" },
     { value: "restore", label: "restore" },
+    { value: "usage", label: "usage" },
   ]);
 });
 
@@ -93,7 +102,7 @@ it("handles no argument as status rather than an invalid default action", async
   expect(context.pi.setModel).not.toHaveBeenCalled();
   await context.command().handler("extend restore", context.ctx);
   expect(context.notify).toHaveBeenLastCalledWith(
-    "Usage: /eleith:codex [extend|restore]",
+    "Usage: /eleith:codex [extend|restore|usage]",
     "warning",
   );
 });
@@ -111,8 +120,50 @@ it("wires restore/reconcile hooks without provider calls for an unsupported mode
   expect(context.pi.setModel).not.toHaveBeenCalled();
   expect(context.pi.appendEntry).not.toHaveBeenCalled();
   expect(context.pi.on.mock.calls.map(([name]) => name)).not.toContain("before_agent_start");
+  expect(fetchCodexUsage).not.toHaveBeenCalled();
 });
 
+it("routes usage through the configured command without requiring an idle Codex selection", async () => {
+  const context = await load("personal");
+  vi.mocked(fetchCodexUsage).mockResolvedValue({ plan_type: "plus" });
+  await context.emit("session_start");
+  await context.command().handler("usage extra", context.ctx);
+  expect(fetchCodexUsage).not.toHaveBeenCalled();
+  context.notify.mockClear();
+  await context.command().handler("usage", { ...context.ctx, isIdle: () => false });
+  expect(fetchCodexUsage).toHaveBeenCalledExactlyOnceWith(
+    context.ctx.modelRegistry,
+    expect.any(AbortSignal),
+  );
+  expect(context.notify).toHaveBeenCalledExactlyOnceWith(
+    expect.stringContaining("Plan: plus"),
+    "info",
+  );
+  expect(context.pi.setModel).not.toHaveBeenCalled();
+  expect(context.pi.appendEntry).not.toHaveBeenCalled();
+});
+
+it.each(["model_select", "session_tree", "session_shutdown"])(
+  "%s cancels a pending usage report instead of displaying a late reply",
+  async (event) => {
+    const context = await load();
+    let finish!: (value: unknown) => void;
+    vi.mocked(fetchCodexUsage).mockReturnValue(
+      new Promise((resolve) => {
+        finish = resolve;
+      }),
+    );
+    await context.emit("session_start");
+    const request = context.command().handler("usage", context.ctx);
+    const signal = vi.mocked(fetchCodexUsage).mock.calls[0][1]!;
+    await context.emit(event);
+    expect(signal.aborted).toBe(true);
+    finish({ plan_type: "plus" });
+    await request;
+    expect(context.notify).not.toHaveBeenCalled();
+  },
+);
+
 it("fails invalid prefix settings before registering any capabilities", async () => {
   writeFileSync(configPath, '{"commandPrefix":"Invalid Prefix"}');
   const on = vi.fn(),
diff --git a/extensions/codex/src/index.ts b/extensions/codex/src/index.ts
index 0d854d7..6fff236 100644
--- a/extensions/codex/src/index.ts
+++ b/extensions/codex/src/index.ts
@@ -2,24 +2,38 @@ import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
 import { registerCommand } from "@eleith/pi-internal/commands";
 import { getSettings } from "@eleith/pi-internal/config";
 import { ContextController } from "./controller.ts";
+import { UsageController } from "./usage-controller.ts";
 
 export default async function codex(pi: ExtensionAPI): Promise<void> {
   const settings = await getSettings();
   const commandName = `${settings.commandPrefix}:codex`;
   const controller = new ContextController(pi, commandName);
+  const usage = new UsageController();
 
   registerCommand(pi, {
     name: commandName,
-    description: "Codex context window controls",
-    actions: ["extend", "restore"],
+    description: "Codex context controls and account usage",
+    actions: ["extend", "restore", "usage"],
     defaultAction: "",
-    handler: (action, ctx) => controller.handle(action, ctx),
+    handler(action, ctx) {
+      if (action === "usage") return usage.report(ctx);
+      return controller.handle(action, ctx);
+    },
   });
 
   pi.on("session_start", (_event, ctx) => controller.restore(ctx));
-  pi.on("session_tree", (_event, ctx) => controller.restore(ctx));
-  pi.on("model_select", (_event, ctx) => controller.modelSelected(ctx));
-  pi.on("session_shutdown", (_event, ctx) => controller.shutdown(ctx));
+  pi.on("session_tree", (_event, ctx) => {
+    usage.cancel();
+    return controller.restore(ctx);
+  });
+  pi.on("model_select", (_event, ctx) => {
+    usage.cancel();
+    return controller.modelSelected(ctx);
+  });
+  pi.on("session_shutdown", (_event, ctx) => {
+    usage.dispose();
+    controller.shutdown(ctx);
+  });
   pi.on("input", async (event, ctx) => {
     if (event.streamingBehavior === undefined && ctx.isIdle()) await controller.reconcile(ctx);
   });
diff --git a/extensions/codex/src/usage-controller.test.ts b/extensions/codex/src/usage-controller.test.ts
new file mode 100644
index 0000000..1663d16
--- /dev/null
+++ b/extensions/codex/src/usage-controller.test.ts
@@ -0,0 +1,146 @@
+import { expect, it, vi } from "vitest";
+import { CodexAccountError, type CodexAccountRegistry, type fetchCodexUsage } from "./client.ts";
+import { UsageController, type UsageHost } from "./usage-controller.ts";
+
+function deferred<T>() {
+  let resolve!: (value: T) => void;
+  let reject!: (error: unknown) => void;
+  const promise = new Promise<T>((done, fail) => {
+    resolve = done;
+    reject = fail;
+  });
+  return { promise, resolve, reject };
+}
+
+function fixture() {
+  const clock = { now: Date.parse("2026-01-10T12:00:00Z") };
+  const fetchUsage = vi.fn<typeof fetchCodexUsage>(async () => ({ plan_type: "plus" }));
+  const ctx = {
+    modelRegistry: {} as CodexAccountRegistry,
+    sessionManager: { getSessionId: vi.fn(() => "session") },
+    ui: { notify: vi.fn() },
+  } satisfies UsageHost;
+  const controller = new UsageController(fetchUsage, () => clock.now);
+  return { controller, ctx, fetchUsage, clock };
+}
+
+it("reports the configured Codex account independently of the selected model", async () => {
+  const f = fixture();
+  await f.controller.report(f.ctx);
+  expect(f.fetchUsage).toHaveBeenCalledExactlyOnceWith(
+    f.ctx.modelRegistry,
+    expect.any(AbortSignal),
+  );
+  expect(f.ctx.ui.notify).toHaveBeenCalledExactlyOnceWith(
+    expect.stringContaining("codex account usage · openai-codex"),
+    "info",
+  );
+});
+
+it("supersedes an earlier request and ignores its late reply", async () => {
+  const f = fixture();
+  const first = deferred<unknown>();
+  f.fetchUsage.mockReturnValueOnce(first.promise).mockResolvedValueOnce({ plan_type: "new-plan" });
+  const oldRequest = f.controller.report(f.ctx);
+  const oldSignal = f.fetchUsage.mock.calls[0][1]!;
+  await f.controller.report(f.ctx);
+  expect(oldSignal.aborted).toBe(true);
+  first.resolve({ plan_type: "old-plan" });
+  await oldRequest;
+  expect(f.ctx.ui.notify).toHaveBeenCalledExactlyOnceWith(
+    expect.stringContaining("Plan: new-plan"),
+    "info",
+  );
+});
+
+it.each(["cancel", "dispose"] as const)(
+  "%s discards a late reply before accessing expired context",
+  async (action) => {
+    const f = fixture();
+    const response = deferred<unknown>();
+    f.fetchUsage.mockReturnValue(response.promise);
+    const request = f.controller.report(f.ctx);
+    const signal = f.fetchUsage.mock.calls[0][1]!;
+    const notify = f.ctx.ui.notify;
+    f.controller[action]();
+    Object.defineProperty(f.ctx, "sessionManager", {
+      get: () => {
+        throw new Error("Expired context");
+      },
+    });
+    Object.defineProperty(f.ctx, "ui", {
+      get: () => {
+        throw new Error("Expired context");
+      },
+    });
+    response.resolve({ plan_type: "plus" });
+    await request;
+    expect(signal.aborted).toBe(true);
+    expect(notify).not.toHaveBeenCalled();
+    if (action === "dispose") await f.controller.report(f.ctx);
+  },
+);
+
+it("disposal suppresses a late error and is idempotent", async () => {
+  const f = fixture();
+  const response = deferred<unknown>();
+  f.fetchUsage.mockReturnValue(response.promise);
+  const request = f.controller.report(f.ctx);
+  f.controller.dispose();
+  f.controller.dispose();
+  response.reject(new Error("private late failure"));
+  await request;
+  await f.controller.report(f.ctx);
+  expect(f.ctx.ui.notify).not.toHaveBeenCalled();
+  expect(f.fetchUsage).toHaveBeenCalledOnce();
+});
+
+it("does not deliver a reply to a replacement session", async () => {
+  const f = fixture();
+  const response = deferred<unknown>();
+  f.fetchUsage.mockReturnValue(response.promise);
+  const request = f.controller.report(f.ctx);
+  f.ctx.sessionManager.getSessionId.mockReturnValue("different-session");
+  response.resolve({ plan_type: "plus" });
+  await request;
+  expect(f.ctx.ui.notify).not.toHaveBeenCalled();
+});
+
+it("reports an unrecognized schema without dumping account data", async () => {
+  const f = fixture();
+  f.fetchUsage.mockResolvedValue({ private_account_data: "do-not-display" });
+  await f.controller.report(f.ctx);
+  expect(f.ctx.ui.notify).toHaveBeenCalledExactlyOnceWith(
+    "Codex account service returned an unrecognized usage response.",
+    "warning",
+  );
+});
+
+it("does not expose unexpected error details", async () => {
+  const f = fixture();
+  f.fetchUsage.mockRejectedValue(new Error("private failure details"));
+  await f.controller.report(f.ctx);
+  expect(f.ctx.ui.notify).toHaveBeenCalledExactlyOnceWith(
+    "Could not read Codex account usage.",
+    "warning",
+  );
+});
+
+it("honors retry-after without polling or making another request until explicitly asked", async () => {
+  const f = fixture();
+  f.fetchUsage.mockRejectedValueOnce(
+    new CodexAccountError("http", "Codex account service is rate limited.", 60_000),
+  );
+  await f.controller.report(f.ctx);
+  await f.controller.report(f.ctx);
+  expect(f.fetchUsage).toHaveBeenCalledOnce();
+  expect(f.ctx.ui.notify).toHaveBeenLastCalledWith(
+    "Codex account service is rate limited. Try again in 60s.",
+    "warning",
+  );
+  f.clock.now += 60_000;
+  expect(f.fetchUsage).toHaveBeenCalledOnce();
+  await f.controller.report(f.ctx);
+  expect(f.fetchUsage).toHaveBeenCalledTimes(2);
+  expect(f.ctx.ui.notify).toHaveBeenLastCalledWith(expect.stringContaining("Plan: plus"), "info");
+});
diff --git a/extensions/codex/src/usage-controller.ts b/extensions/codex/src/usage-controller.ts
new file mode 100644
index 0000000..02a55de
--- /dev/null
+++ b/extensions/codex/src/usage-controller.ts
@@ -0,0 +1,69 @@
+import type { ExtensionContext } from "@earendil-works/pi-coding-agent";
+import { CodexAccountError, fetchCodexUsage, type CodexAccountRegistry } from "./client.ts";
+import { formatCodexUsage } from "./usage.ts";
+
+export interface UsageHost {
+  readonly modelRegistry: CodexAccountRegistry;
+  readonly sessionManager: Pick<ExtensionContext["sessionManager"], "getSessionId">;
+  readonly ui: Pick<ExtensionContext["ui"], "notify">;
+}
+
+export class UsageController {
+  private pending: AbortController | undefined;
+  private retryAt = 0;
+  private disposed = false;
+
+  constructor(
+    private readonly fetchUsage: typeof fetchCodexUsage = fetchCodexUsage,
+    private readonly now: () => number = Date.now,
+  ) {}
+
+  async report(ctx: UsageHost): Promise<void> {
+    if (this.disposed) return;
+    this.cancel();
+    if (this.now() < this.retryAt) {
+      const seconds = Math.ceil((this.retryAt - this.now()) / 1000);
+      ctx.ui.notify(`Codex account service is rate limited. Try again in ${seconds}s.`, "warning");
+      return;
+    }
+    const sessionId = ctx.sessionManager.getSessionId();
+    const operation = new AbortController();
+    this.pending = operation;
+    try {
+      const data = await this.fetchUsage(ctx.modelRegistry, operation.signal);
+      if (!this.canDeliverReport(operation, ctx, sessionId)) return;
+      const report = formatCodexUsage(data, this.now());
+      if (report === undefined) {
+        ctx.ui.notify("Codex account service returned an unrecognized usage response.", "warning");
+      } else {
+        ctx.ui.notify(report, "info");
+      }
+    } catch (error) {
+      if (!this.canDeliverReport(operation, ctx, sessionId)) return;
+      const message =
+        error instanceof CodexAccountError ? error.message : "Could not read Codex account usage.";
+      if (error instanceof CodexAccountError && error.retryAfterMs !== undefined) {
+        this.retryAt = this.now() + error.retryAfterMs;
+      }
+      ctx.ui.notify(message, "warning");
+    } finally {
+      if (this.pending === operation) this.pending = undefined;
+    }
+  }
+
+  cancel(): void {
+    this.pending?.abort();
+    this.pending = undefined;
+  }
+
+  dispose(): void {
+    if (this.disposed) return;
+    this.disposed = true;
+    this.cancel();
+  }
+
+  private canDeliverReport(operation: AbortController, ctx: UsageHost, sessionId: string): boolean {
+    if (this.disposed || this.pending !== operation || operation.signal.aborted) return false;
+    return ctx.sessionManager.getSessionId() === sessionId;
+  }
+}
diff --git a/extensions/codex/src/usage-sdk.test.ts b/extensions/codex/src/usage-sdk.test.ts
new file mode 100644
index 0000000..63c1427
--- /dev/null
+++ b/extensions/codex/src/usage-sdk.test.ts
@@ -0,0 +1,169 @@
+import { rmSync } from "node:fs";
+import { afterAll, expect, it, vi } from "vitest";
+import {
+  InMemoryModelsStore,
+  type Api,
+  type CredentialStore,
+  type Model,
+  type OAuthCredential,
+} from "@earendil-works/pi-ai";
+import {
+  createAgentSession,
+  DefaultResourceLoader,
+  ModelRuntime,
+  SessionManager,
+  SettingsManager,
+  type ExtensionUIContext,
+} from "@earendil-works/pi-coding-agent";
+import codex from "./index.ts";
+
+const directory = await vi.hoisted(async () => {
+  const { mkdtempSync } = await import("node:fs");
+  const { tmpdir } = await import("node:os");
+  const { join } = await import("node:path");
+  const directory = mkdtempSync(join(tmpdir(), "codex-usage-sdk-test-"));
+  vi.stubEnv("PI_CODING_AGENT_DIR", directory);
+  vi.stubEnv("PI_OFFLINE", "1");
+  return directory;
+});
+afterAll(() => {
+  vi.unstubAllGlobals();
+  vi.unstubAllEnvs();
+  rmSync(directory, { recursive: true, force: true });
+});
+
+it("SDK usage reuses Pi's OAuth without a model turn or credential write", async () => {
+  const usageResponse = {
+    plan_type: "plus",
+    rate_limit: {
+      primary_window: {
+        used_percent: 25,
+        limit_window_seconds: 18_000,
+        reset_after_seconds: 1800,
+      },
+    },
+  };
+  const accountRequest = vi.fn<typeof fetch>(async (url) => {
+    if (url !== "https://chatgpt.com/backend-api/wham/usage") {
+      throw new Error("Unexpected network request");
+    }
+    return new Response(JSON.stringify(usageResponse));
+  });
+  vi.stubGlobal("fetch", accountRequest);
+  const { runtime, model, accessToken, credentialWrites, modelTurns } =
+    await createOfflineCodexRuntime();
+  const { session, sessionManager, notify, extensionErrors, closeSession } =
+    await openCodexExtensionSession(runtime, model);
+  try {
+    const branch = structuredClone(sessionManager.getBranch());
+    await session.prompt("/eleith:codex");
+    expect(accountRequest).not.toHaveBeenCalled();
+
+    await session.prompt("/eleith:codex usage");
+    expect(notify).toHaveBeenLastCalledWith(
+      expect.stringContaining("Primary (5h): 25% used"),
+      "info",
+    );
+    expect(accountRequest).toHaveBeenCalledOnce();
+    const headers = new Headers(accountRequest.mock.calls[0][1]?.headers);
+    expect(headers.get("authorization")).toBe(`Bearer ${accessToken}`);
+    expect(headers.get("chatgpt-account-id")).toBe("sdk-test-account");
+    expect(sessionManager.getBranch()).toEqual(branch);
+    expect(session.model).toEqual(model);
+    expect(credentialWrites).not.toHaveBeenCalled();
+    expect(modelTurns).not.toHaveBeenCalled();
+    expect(extensionErrors).toEqual([]);
+  } finally {
+    await closeSession();
+  }
+});
+
+async function createOfflineCodexRuntime() {
+  const payload = { "https://api.openai.com/auth": { chatgpt_account_id: "sdk-test-account" } };
+  const accessToken = `e30.${Buffer.from(JSON.stringify(payload)).toString("base64url")}.fake-signature`;
+  const credential: OAuthCredential = {
+    type: "oauth",
+    access: accessToken,
+    refresh: "must-not-refresh",
+    expires: Date.now() + 3_600_000,
+  };
+  const credentialWrites = vi.fn<CredentialStore["modify"]>(async () => {
+    throw new Error("Credential writes forbidden");
+  });
+  const credentials: CredentialStore = {
+    read: async (id) => (id === "openai-codex" ? credential : undefined),
+    list: async () => [{ providerId: "openai-codex", type: "oauth" }],
+    modify: credentialWrites,
+    delete: async () => {
+      throw new Error("Credential deletion forbidden");
+    },
+  };
+  const runtime = await ModelRuntime.create({
+    credentials,
+    modelsPath: null,
+    modelsStore: new InMemoryModelsStore(),
+    allowModelNetwork: false,
+    refreshOnCreate: false,
+  });
+  // Populate Pi's auth-availability snapshot without probing other providers or the network.
+  const refresh = await runtime.refresh({ providers: ["openai-codex"], allowNetwork: false });
+  expect(refresh.errors.size).toBe(0);
+  expect(runtime.isUsingOAuth("openai-codex")).toBe(true);
+  const modelTurns = vi.spyOn(runtime, "streamSimple").mockImplementation(() => {
+    throw new Error("Model turns forbidden");
+  });
+  const model = runtime.getModel("openai-codex", "gpt-6-sol");
+  if (!model) throw new Error("Built-in Codex model missing");
+  return { runtime, model, accessToken, credentialWrites, modelTurns };
+}
+
+async function openCodexExtensionSession(runtime: ModelRuntime, model: Model<Api>) {
+  const settingsManager = SettingsManager.inMemory({
+    packages: [],
+    enableInstallTelemetry: false,
+    enableAnalytics: false,
+    compaction: { enabled: false },
+    retry: { enabled: false },
+    cacheWarming: "off",
+  });
+  const resourceLoader = new DefaultResourceLoader({
+    cwd: directory,
+    agentDir: directory,
+    settingsManager,
+    noExtensions: true,
+    noSkills: true,
+    noPromptTemplates: true,
+    noThemes: true,
+    noContextFiles: true,
+    extensionFactories: [codex],
+  });
+  await resourceLoader.reload();
+  const sessionManager = SessionManager.inMemory(directory);
+  const { session } = await createAgentSession({
+    cwd: directory,
+    agentDir: directory,
+    resourceLoader,
+    settingsManager,
+    modelRuntime: runtime,
+    model,
+    sessionManager,
+    noTools: "all",
+  });
+  const notify = vi.fn();
+  const extensionErrors: unknown[] = [];
+  await session.bindExtensions({
+    mode: "tui",
+    uiContext: { notify } as unknown as ExtensionUIContext,
+    onError: (error) => extensionErrors.push(error),
+  });
+  return {
+    session,
+    sessionManager,
+    notify,
+    extensionErrors,
+    async closeSession() {
+      await session.extensionRunner.emit({ type: "session_shutdown", reason: "quit" });
+      session.dispose();
+    },
+  };
+}
diff --git a/extensions/codex/src/usage.test.ts b/extensions/codex/src/usage.test.ts
new file mode 100644
index 0000000..2283ad1
--- /dev/null
+++ b/extensions/codex/src/usage.test.ts
@@ -0,0 +1,154 @@
+import { expect, it } from "vitest";
+import { formatCodexUsage } from "./usage.ts";
+
+const NOW = Date.parse("2026-01-10T12:00:00Z");
+const primary = {
+  used_percent: 25,
+  limit_window_seconds: 1800,
+  reset_at: NOW / 1000 + 3600,
+};
+
+it("formats an exact account report without mutating the payload", () => {
+  const payload = {
+    plan_type: "plus",
+    account_id: "do-not-display-account-id",
+    rate_limit: { allowed: true, primary_window: primary, secondary_window: null },
+    credits: { has_credits: true, unlimited: false, balance: "12.50" },
+    future_field: { anything: true },
+  };
+  const original = structuredClone(payload);
+  const report = formatCodexUsage(payload, NOW)!;
+  expect(report).toBe(`codex account usage · openai-codex
+Plan: plus
+
+Codex
+  Primary (30m): 25% used · 75% remaining
+    Resets: 2026-01-10 13:00:00 UTC (in 1h)
+  Secondary: not reported
+
+Credits: 12.5 balance (available)`);
+  expect(payload).toEqual(original);
+});
+
+it("does not invent windows or unlimited credits for plans with missing quota data", () => {
+  const report = formatCodexUsage(
+    {
+      plan_type: "pro",
+      rate_limit: null,
+      code_review_rate_limit: null,
+      credits: null,
+    },
+    NOW,
+  )!;
+  expect(report).toContain("Codex\n  Not reported");
+  expect(report).toContain("Code review\n  Not reported");
+  expect(report).toContain("Credits: not reported");
+  expect(report).not.toMatch(/0%|5h|7d|unlimited/);
+});
+
+it.each([
+  [0, "0% used · 100% remaining"],
+  [-1, "usage unknown"],
+  [101, "usage unknown"],
+  [NaN, "usage unknown"],
+  ["25", "usage unknown"],
+] as const)("keeps invalid percentages distinct from genuine zero: %s", (used, expected) => {
+  const report = formatCodexUsage(
+    {
+      rate_limit: { primary_window: { ...primary, used_percent: used } },
+    },
+    NOW,
+  )!;
+  expect(report).toContain(expected);
+});
+
+it("uses supplied relative resets without guessing a window duration", () => {
+  const report = formatCodexUsage(
+    {
+      rate_limit: {
+        primary_window: {
+          used_percent: 40,
+          limit_window_seconds: "18000",
+          reset_after_seconds: 90,
+        },
+      },
+    },
+    NOW,
+  )!;
+  expect(report).toContain("Primary (duration unknown): 40% used · 60% remaining");
+  expect(report).toContain("2026-01-10 12:01:30 UTC (in 1m 30s)");
+});
+
+it("reports unknown invalid reset times and never resets a measured balance locally", () => {
+  const report = formatCodexUsage(
+    {
+      rate_limit: {
+        limit_reached: true,
+        primary_window: { ...primary, used_percent: 100, reset_at: NOW / 1000 - 1 },
+        secondary_window: { ...primary, reset_at: Infinity },
+      },
+    },
+    NOW,
+  )!;
+  expect(report).toContain("100% used · 0% remaining");
+  expect(report).toContain("reset time passed; refresh usage");
+  expect(report).toContain("Resets: unknown");
+  expect(report).toContain("Limit reached");
+});
+
+it.each([
+  [{ unlimited: true }, "unlimited"],
+  [{ unlimited: true, has_credits: false }, "unlimited (unavailable)"],
+  [{ has_credits: false, balance: "0" }, "0 balance (unavailable)"],
+  [{ has_credits: true }, "available; balance not reported"],
+  [{ has_credits: false, balance: "0x10" }, "unavailable; balance not reported"],
+] as const)("reports only supplied credit facts: %j", (credits, expected) => {
+  expect(formatCodexUsage({ credits }, NOW)).toContain(`Credits: ${expected}`);
+});
+
+it("includes review and additional buckets plus explicit account restrictions", () => {
+  const report = formatCodexUsage(
+    {
+      code_review_rate_limit: { primary_window: { ...primary, limit_window_seconds: 604_800 } },
+      additional_rate_limits: [
+        {
+          metered_feature: "codex_other",
+          limit_name: "Other model pool",
+          rate_limit: { allowed: false, primary_window: primary },
+        },
+      ],
+      spend_control: { reached: true },
+      rate_limit_reached_type: { type: "workspace_owner_credits_depleted" },
+    },
+    NOW,
+  )!;
+  expect(report).toContain("Code review\n  Primary (7d)");
+  expect(report).toContain("Other model pool\n  Primary (30m)");
+  expect(report).toContain("Requests not currently allowed");
+  expect(report).toContain("Workspace spending limit: reached");
+  expect(report).toContain("Account limit: workspace owner credits depleted");
+});
+
+it("bounds and sanitizes backend labels and additional-bucket output", () => {
+  const payload = {
+    plan_type: "plus\u001b[31m\n",
+    additional_rate_limits: Array.from({ length: 10 }, (_, index) => ({
+      limit_name: `Pool ${index}\r\n${"x".repeat(1000)}`,
+      rate_limit: { primary_window: primary },
+    })),
+  };
+  const report = formatCodexUsage(payload, NOW)!;
+  // oxlint-disable-next-line no-control-regex -- Newlines are layout; other terminal controls must be absent.
+  expect(report).not.toMatch(/[\x00-\x09\x0b-\x1f\x7f-\x9f]/);
+  expect(report).not.toContain("x".repeat(65));
+  expect(report).toContain("2 additional entries omitted.");
+  expect(report).not.toContain("Pool 8");
+  expect(report.length).toBeLessThan(5000);
+});
+
+it.each([null, [], {}, { unrelated: 10 }, { rate_limit: "wrong shape" }])(
+  "rejects unrecognized response shapes instead of fabricating healthy usage: %j",
+  (payload) => {
+    expect(formatCodexUsage(payload, NOW)).toBeUndefined();
+  },
+);
diff --git a/extensions/codex/src/usage.ts b/extensions/codex/src/usage.ts
new file mode 100644
index 0000000..0ae2b28
--- /dev/null
+++ b/extensions/codex/src/usage.ts
@@ -0,0 +1,197 @@
+const MAX_ADDITIONAL_BUCKETS = 8;
+const MAX_LABEL_LENGTH = 64;
+const NUMBERS = new Intl.NumberFormat("en-US", { maximumFractionDigits: 2 });
+
+type JsonObject = Record<string, unknown>;
+
+interface UsageSections {
+  plan: string | undefined;
+  codex: JsonObject | undefined;
+  includeCodeReview: boolean;
+  codeReview: JsonObject | undefined;
+  additional: unknown[] | undefined;
+  credits: JsonObject | undefined;
+  spendingLimitReached: boolean;
+  accountLimit: string | undefined;
+}
+
+/** Account allowance only; this is not Pi's context occupancy or a cost estimate. */
+export function formatCodexUsage(value: unknown, now = Date.now()): string | undefined {
+  const sections = readUsageSections(value);
+  if (!sections) return undefined;
+
+  const rows = [
+    "codex account usage · openai-codex",
+    `Plan: ${sections.plan ?? "unknown"}`,
+    "",
+    ...bucketRows("Codex", sections.codex, now),
+  ];
+  if (sections.includeCodeReview) {
+    rows.push("", ...bucketRows("Code review", sections.codeReview, now));
+  }
+  rows.push(...additionalBucketRows(sections.additional, now));
+  rows.push("", `Credits: ${creditStatus(sections.credits)}`);
+  if (sections.spendingLimitReached) rows.push("Workspace spending limit: reached");
+  if (sections.accountLimit)
+    rows.push(`Account limit: ${sections.accountLimit.replaceAll("_", " ")}`);
+  return rows.join("\n");
+}
+
+function readUsageSections(value: unknown): UsageSections | undefined {
+  const payload = readObject(value);
+  if (!payload) return undefined;
+
+  const plan = sanitizeDisplayLabel(payload.plan_type);
+  const codex = readObject(payload.rate_limit);
+  const codeReview = readObject(payload.code_review_rate_limit);
+  const credits = readObject(payload.credits);
+  const spendingControl = readObject(payload.spend_control);
+  const reachedLimit = readObject(payload.rate_limit_reached_type);
+  const additional = Array.isArray(payload.additional_rate_limits)
+    ? payload.additional_rate_limits
+    : undefined;
+  const hasUsageData = [
+    plan,
+    codex,
+    codeReview,
+    credits,
+    spendingControl,
+    reachedLimit,
+    additional,
+  ].some((section) => section !== undefined);
+  if (!hasUsageData) return undefined;
+
+  const includeCodeReview = "code_review_rate_limit" in payload;
+  const spendingLimitReached = spendingControl?.reached === true;
+  const accountLimit = sanitizeDisplayLabel(reachedLimit?.type);
+  return {
+    plan,
+    codex,
+    includeCodeReview,
+    codeReview,
+    additional,
+    credits,
+    spendingLimitReached,
+    accountLimit,
+  };
+}
+
+function bucketRows(name: string, bucket: JsonObject | undefined, now: number): string[] {
+  if (!bucket) return [name, "  Not reported"];
+  const rows = [
+    name,
+    ...windowRows("Primary", bucket.primary_window, now),
+    ...windowRows("Secondary", bucket.secondary_window, now),
+  ];
+  if (bucket.limit_reached === true) rows.push("  Limit reached");
+  else if (bucket.allowed === false) rows.push("  Requests not currently allowed");
+  return rows;
+}
+
+function windowRows(name: string, value: unknown, now: number): string[] {
+  const window = readObject(value);
+  if (!window) return [`  ${name}: not reported`];
+
+  const seconds = finiteNonnegativeNumber(window.limit_window_seconds);
+  let interval = "duration unknown";
+  if (seconds !== undefined && Number.isSafeInteger(seconds) && seconds > 0)
+    interval = duration(seconds);
+  const used = finiteNonnegativeNumber(window.used_percent);
+  let usage = "usage unknown";
+  if (used !== undefined && used <= 100) {
+    usage = `${NUMBERS.format(used)}% used · ${NUMBERS.format(100 - used)}% remaining`;
+  }
+  return [`  ${name} (${interval}): ${usage}`, `    Resets: ${resetTime(window, now)}`];
+}
+
+function additionalBucketRows(additional: unknown[] | undefined, now: number): string[] {
+  if (!additional) return [];
+  const rows: string[] = [];
+  for (const [index, value] of additional.slice(0, MAX_ADDITIONAL_BUCKETS).entries()) {
+    const entry = readObject(value);
+    const name =
+      sanitizeDisplayLabel(entry?.limit_name) ??
+      sanitizeDisplayLabel(entry?.metered_feature) ??
+      `Additional ${index + 1}`;
+    const quota = readObject(entry?.rate_limit);
+    rows.push("", ...bucketRows(name, quota, now));
+  }
+  if (additional.length > MAX_ADDITIONAL_BUCKETS) {
+    rows.push("", `${additional.length - MAX_ADDITIONAL_BUCKETS} additional entries omitted.`);
+  }
+  return rows;
+}
+
+function creditStatus(credits: JsonObject | undefined): string {
+  if (!credits) return "not reported";
+  if (credits.unlimited === true) {
+    return credits.has_credits === false ? "unlimited (unavailable)" : "unlimited";
+  }
+  let availability = "availability unknown";
+  if (credits.has_credits === true) availability = "available";
+  else if (credits.has_credits === false) availability = "unavailable";
+  const balance = parseCreditBalance(credits.balance);
+  if (balance === undefined) return `${availability}; balance not reported`;
+  return `${NUMBERS.format(balance)} balance (${availability})`;
+}
+
+function parseCreditBalance(value: unknown): number | undefined {
+  if (typeof value === "number") return finiteNonnegativeNumber(value);
+  if (typeof value !== "string") return undefined;
+  const decimal = value.trim();
+  if (!/^\d+(?:\.\d+)?$/.test(decimal)) return undefined;
+  return finiteNonnegativeNumber(Number(decimal));
+}
+
+function resetTime(window: JsonObject, now: number): string {
+  const absolute = finiteNonnegativeNumber(window.reset_at);
+  const relative = finiteNonnegativeNumber(window.reset_after_seconds);
+  let timestamp = NaN;
+  if (absolute !== undefined) timestamp = absolute * 1000;
+  else if (relative !== undefined) timestamp = now + relative * 1000;
+  const date = new Date(timestamp);
+  if (!Number.isFinite(date.getTime())) return "unknown";
+  const time = date.toISOString().replace("T", " ").replace(".000Z", " UTC");
+  const remaining = Math.ceil((timestamp - now) / 1000);
+  return remaining > 0
+    ? `${time} (in ${duration(remaining)})`
+    : `${time} (reset time passed; refresh usage)`;
+}
+
+function duration(seconds: number): string {
+  let remaining = Math.ceil(seconds);
+  const parts: string[] = [];
+  for (const [unit, size] of [
+    ["d", 86_400],
+    ["h", 3600],
+    ["m", 60],
+    ["s", 1],
+  ] as const) {
+    const amount = Math.floor(remaining / size);
+    if (amount > 0) parts.push(`${amount}${unit}`);
+    remaining %= size;
+  }
+  return parts.join(" ") || "0s";
+}
+
+function readObject(value: unknown): JsonObject | undefined {
+  return value !== null && typeof value === "object" && !Array.isArray(value)
+    ? (value as JsonObject)
+    : undefined;
+}
+
+function sanitizeDisplayLabel(value: unknown): string | undefined {
+  if (typeof value !== "string") return undefined;
+  return (
+    value
+      // oxlint-disable-next-line no-control-regex -- Strip terminal controls from backend labels.
+      .replace(/[\x00-\x1f\x7f-\x9f]/g, " ")
+      .replace(/\s+/g, " ")
+      .trim()
+      .slice(0, MAX_LABEL_LENGTH) || undefined
+  );
+}
+
+function finiteNonnegativeNumber(value: unknown): number | undefined {
+  return typeof value === "number" && Number.isFinite(value) && value >= 0 ? value : undefined;
+}