diff --git a/src/main/commitMessageProviders.test.ts b/src/main/commitMessageProviders.test.ts
index 0ef49fd..918847b 100644
--- a/src/main/commitMessageProviders.test.ts
+++ b/src/main/commitMessageProviders.test.ts
@@ -50,6 +50,79 @@ afterEach(() => {
 });
 
 describe("commit message provider cancellation", () => {
+  it.each(apiProviderFactories)("keeps $name active while response bytes arrive for more than a minute", async ({ create }) => {
+    vi.useFakeTimers();
+    let body!: ReadableStreamDefaultController<Uint8Array>;
+    const response = new Response(new ReadableStream<Uint8Array>({
+      start(controller) { body = controller; }
+    }));
+    const provider = create(async () => response);
+    const generation = provider.generate(providerInput);
+    const result = generation.catch((error: unknown) => error);
+    const encoder = new TextEncoder();
+    for (let index = 0; index < 3; index += 1) {
+      await vi.advanceTimersByTimeAsync(30_000);
+      body.enqueue(encoder.encode(" "));
+    }
+    body.enqueue(encoder.encode(JSON.stringify({
+      choices: [{ message: { content: "feat: café" } }],
+      output_text: "feat: café",
+      content: [{ type: "text", text: "feat: café" }]
+    })));
+    body.close();
+    expect(await result).toMatchObject({ text: "feat: café" });
+    expect(vi.getTimerCount()).toBe(0);
+  });
+
+  it.each(apiProviderFactories)("times out $name after response activity stops", async ({ create }) => {
+    vi.useFakeTimers();
+    let body!: ReadableStreamDefaultController<Uint8Array>;
+    const cancel = vi.fn();
+    const response = new Response(new ReadableStream<Uint8Array>({
+      start(controller) { body = controller; },
+      cancel
+    }));
+    const provider = create(async () => response);
+    const settled = vi.fn();
+    const result = provider.generate(providerInput).catch((error: unknown) => error).then((value) => {
+      settled();
+      return value;
+    });
+    await vi.advanceTimersByTimeAsync(30_000);
+    body.enqueue(new TextEncoder().encode(" "));
+    await vi.advanceTimersByTimeAsync(59_999);
+    expect(settled).not.toHaveBeenCalled();
+    // Empty chunks do not indicate response progress.
+    body.enqueue(new Uint8Array());
+    await vi.advanceTimersByTimeAsync(1);
+    expect(await result).toMatchObject({ name: "TimeoutError" });
+    expect(cancel).toHaveBeenCalledOnce();
+    expect(response.body?.locked).toBe(false);
+    expect(vi.getTimerCount()).toBe(0);
+  });
+
+  it.each(apiProviderFactories)("cancels $name after response activity extends the request", async ({ create }) => {
+    vi.useFakeTimers();
+    const controller = new AbortController();
+    let body!: ReadableStreamDefaultController<Uint8Array>;
+    const cancel = vi.fn();
+    const response = new Response(new ReadableStream<Uint8Array>({
+      start(streamController) { body = streamController; },
+      cancel
+    }));
+    const provider = create(async () => response);
+    const result = provider.generate({ ...providerInput, signal: controller.signal }).catch((error: unknown) => error);
+    await vi.advanceTimersByTimeAsync(30_000);
+    body.enqueue(new TextEncoder().encode(" "));
+    await vi.advanceTimersByTimeAsync(40_000);
+    const reason = new DOMException("Generation cancelled.", "AbortError");
+    controller.abort(reason);
+    expect(await result).toBe(reason);
+    expect(cancel).toHaveBeenCalledWith(reason);
+    expect(response.body?.locked).toBe(false);
+    expect(vi.getTimerCount()).toBe(0);
+  });
+
   it("propagates an external abort to an in-flight API request", async () => {
     const controller = new AbortController();
     let requestStarted!: () => void;
diff --git a/src/main/commitMessageProviders.ts b/src/main/commitMessageProviders.ts
index f38d0fb..855aa08 100644
--- a/src/main/commitMessageProviders.ts
+++ b/src/main/commitMessageProviders.ts
@@ -163,6 +163,7 @@ export class OpenRouterCommitMessageProvider implements CommitMessageProvider {
       })
     }, {
       timeoutMs: API_TIMEOUT_MS,
+      timeoutMode: "inactivity",
       timeoutReason: createApiTimeoutReason(),
       ...(input.signal ? { signal: input.signal } : {}),
       createJsonFallback: () => ({} as OpenRouterResponse)
@@ -193,6 +194,7 @@ export class OpenAiCommitMessageProvider implements CommitMessageProvider {
       })
     }, {
       timeoutMs: API_TIMEOUT_MS,
+      timeoutMode: "inactivity",
       timeoutReason: createApiTimeoutReason(),
       ...(input.signal ? { signal: input.signal } : {}),
       createJsonFallback: () => ({} as OpenAiResponse)
@@ -242,6 +244,7 @@ export class AnthropicCommitMessageProvider implements CommitMessageProvider {
       })
     }, {
       timeoutMs: API_TIMEOUT_MS,
+      timeoutMode: "inactivity",
       timeoutReason: createApiTimeoutReason(),
       ...(input.signal ? { signal: input.signal } : {}),
       createJsonFallback: () => ({} as AnthropicResponse)
diff --git a/src/main/fetchJsonWithTimeout.ts b/src/main/fetchJsonWithTimeout.ts
index 121622a..615fe99 100644
--- a/src/main/fetchJsonWithTimeout.ts
+++ b/src/main/fetchJsonWithTimeout.ts
@@ -2,6 +2,8 @@ type Fetch = typeof fetch;
 
 export interface FetchJsonWithTimeoutOptions<T> {
   timeoutMs: number;
+  /** Inactivity mode resets the timeout on headers and non-empty body chunks. */
+  timeoutMode?: "total" | "inactivity";
   signal?: AbortSignal;
   timeoutReason?: unknown;
   createJsonFallback?: () => T;
@@ -47,7 +49,9 @@ export async function fetchJsonWithTimeout<T>(
       ...init,
       signal: controller.signal
     }), controller.signal);
-    const payload = await parseJson(response, controller.signal, options.createJsonFallback);
+    const onActivity = options.timeoutMode === "inactivity" ? () => { timeout.refresh(); } : undefined;
+    onActivity?.();
+    const payload = await parseJson(response, controller.signal, options.createJsonFallback, onActivity);
     return { response, payload };
   } catch (error) {
     if (controller.signal.aborted) {
@@ -65,10 +69,34 @@ export async function fetchJsonWithTimeout<T>(
 async function parseJson<T>(
   response: Response,
   signal: AbortSignal,
-  createFallback: (() => T) | undefined
+  createFallback: (() => T) | undefined,
+  onActivity: (() => void) | undefined
 ): Promise<T> {
   try {
-    return await raceWithAbort(response.json() as Promise<T>, signal);
+    if (!onActivity || !response.body) {
+      return await raceWithAbort(response.json() as Promise<T>, signal);
+    }
+    const reader = response.body.getReader();
+    const decoder = new TextDecoder();
+    const chunks: string[] = [];
+    try {
+      while (true) {
+        const { done, value } = await raceWithAbort(reader.read(), signal);
+        if (done) break;
+        if (value.byteLength > 0) {
+          onActivity();
+          chunks.push(decoder.decode(value, { stream: true }));
+        }
+      }
+      chunks.push(decoder.decode());
+      return JSON.parse(chunks.join("")) as T;
+    } finally {
+      if (signal.aborted) {
+        // Cancellation must not wait for an unresponsive underlying stream.
+        void reader.cancel(signal.reason).catch(() => undefined);
+      }
+      reader.releaseLock();
+    }
   } catch (error) {
     if (signal.aborted) {
       throw signal.reason;