diff --git a/packages/ai/CHANGELOG.md b/packages/ai/CHANGELOG.md
index 597bba9b..ec294b77 100644
--- a/packages/ai/CHANGELOG.md
+++ b/packages/ai/CHANGELOG.md
@@ -6,6 +6,10 @@
 
 - Added an optional `reasoning` field to `Usage` reporting reasoning/thinking token counts as a subset of `output`. Populated for Anthropic (`output_tokens_details.thinking_tokens`), OpenAI Responses/Codex/Azure (`output_tokens_details.reasoning_tokens`), OpenAI Completions (`completion_tokens_details.reasoning_tokens`), and Google Generative AI / Vertex (`thoughtsTokenCount`). Bedrock Converse and Mistral are not populated because those APIs do not return a reasoning token breakdown ([#6057](https://github.com/earendil-works/pi/issues/6057)).
 
+### Changed
+
+- Changed OpenAI Codex Responses SSE response-header waits to use the configured HTTP timeout instead of the previous fixed 20 second timeout, reducing false timeouts on slow connections ([#4945](https://github.com/earendil-works/pi/issues/4945)).
+
 ### Fixed
 
 - Fixed `streamSimple()` to send a context-aware max-token cap so providers that count input and output against one context window do not reject long requests ([#5595](https://github.com/earendil-works/pi/issues/5595)).
diff --git a/packages/ai/src/api/openai-codex-responses.ts b/packages/ai/src/api/openai-codex-responses.ts
index 267fa90b..6846cedf 100644
--- a/packages/ai/src/api/openai-codex-responses.ts
+++ b/packages/ai/src/api/openai-codex-responses.ts
@@ -56,9 +56,6 @@ const JWT_CLAIM_PATH = "https://api.openai.com/auth" as const;
 const DEFAULT_MAX_RETRIES = 0;
 const BASE_DELAY_MS = 1000;
 const DEFAULT_MAX_RETRY_DELAY_MS = 60_000;
-// Keep a bounded pre-header timeout so zero-event Codex SSE stalls fail instead of
-// leaving callers stuck on "Working..." indefinitely. See #4945.
-const DEFAULT_SSE_HEADER_TIMEOUT_MS = 20_000;
 const DEFAULT_WEBSOCKET_CONNECT_TIMEOUT_MS = 15_000;
 const CODEX_TOOL_CALL_PROVIDERS = new Set(["openai", "openai-codex", "opencode"]);
 const WEBSOCKET_MESSAGE_TOO_BIG_CLOSE_CODE = 1009;
@@ -179,20 +176,6 @@ function normalizeTimeoutMs(value: number | undefined): number | undefined {
 	return Math.floor(value);
 }
 
-function createSSEHeaderTimeout(): { signal: AbortSignal; clear: () => void; error: () => Error | undefined } {
-	const controller = new AbortController();
-	let error: Error | undefined;
-	const timeout = setTimeout(() => {
-		error = new Error(`Codex SSE response headers timed out after ${DEFAULT_SSE_HEADER_TIMEOUT_MS}ms`);
-		controller.abort(error);
-	}, DEFAULT_SSE_HEADER_TIMEOUT_MS);
-	return {
-		signal: controller.signal,
-		clear: () => clearTimeout(timeout),
-		error: () => error,
-	};
-}
-
 // ============================================================================
 // Main Stream Function
 // ============================================================================
@@ -245,7 +228,7 @@ export const stream: StreamFunction<"openai-codex-responses", OpenAICodexRespons
 				websocketRequestId,
 			);
 			const bodyJson = JSON.stringify(body);
-			const idleTimeoutMs = normalizeTimeoutMs(options?.timeoutMs);
+			const httpTimeoutMs = normalizeTimeoutMs(options?.timeoutMs);
 			const websocketConnectTimeoutMs = normalizeTimeoutMs(options?.websocketConnectTimeoutMs);
 			const transport = options?.transport || "auto";
 			const websocketDisabledForSession = transport !== "sse" && isWebSocketSseFallbackActive(options?.sessionId);
@@ -269,7 +252,7 @@ export const stream: StreamFunction<"openai-codex-responses", OpenAICodexRespons
 							() => {
 								websocketStarted = true;
 							},
-							idleTimeoutMs,
+							httpTimeoutMs,
 							websocketConnectTimeoutMs,
 							options,
 						);
@@ -325,8 +308,9 @@ export const stream: StreamFunction<"openai-codex-responses", OpenAICodexRespons
 				}
 
 				try {
-					const headerTimeout = createSSEHeaderTimeout();
-					const combinedSignal = combineAbortSignals([options?.signal, headerTimeout.signal]);
+					const headerTimeoutSignal =
+						httpTimeoutMs !== undefined && httpTimeoutMs > 0 ? AbortSignal.timeout(httpTimeoutMs) : undefined;
+					const combinedSignal = combineAbortSignals([options?.signal, headerTimeoutSignal]);
 					try {
 						response = await fetch(resolveCodexUrl(model.baseUrl), {
 							method: "POST",
@@ -335,11 +319,12 @@ export const stream: StreamFunction<"openai-codex-responses", OpenAICodexRespons
 							signal: combinedSignal.signal,
 						});
 					} catch (error) {
-						const timeoutError = headerTimeout.error();
-						throw timeoutError && !options?.signal?.aborted ? timeoutError : error;
+						if (headerTimeoutSignal?.aborted && !options?.signal?.aborted) {
+							throw new Error(`Codex SSE response headers timed out after ${httpTimeoutMs}ms`);
+						}
+						throw error;
 					} finally {
 						combinedSignal.cleanup();
-						headerTimeout.clear();
 					}
 					await options?.onResponse?.(
 						{ status: response.status, headers: headersToRecord(response.headers) },
diff --git a/packages/ai/test/openai-codex-stream.test.ts b/packages/ai/test/openai-codex-stream.test.ts
index b68d5b73..bc0d83ca 100644
--- a/packages/ai/test/openai-codex-stream.test.ts
+++ b/packages/ai/test/openai-codex-stream.test.ts
@@ -311,8 +311,7 @@ describe("openai-codex streaming", () => {
 		expect(result.stopReason).toBe("length");
 	});
 
-	it("aborts SSE fetch when response headers do not arrive", async () => {
-		vi.useFakeTimers();
+	it("aborts SSE fetch after the configured HTTP timeout when response headers do not arrive", async () => {
 		const token = mockToken();
 
 		const fetchMock = vi.fn((input: string | URL, init?: RequestInit) => {
@@ -357,25 +356,15 @@ describe("openai-codex streaming", () => {
 			messages: [{ role: "user", content: "Say hello", timestamp: Date.now() }],
 		};
 
-		const resultPromise = streamOpenAICodexResponses(model, context, {
+		const result = await streamOpenAICodexResponses(model, context, {
 			apiKey: token,
 			transport: "sse",
+			timeoutMs: 10,
 		}).result();
-		let settled = false;
-		const observedResultPromise = resultPromise.then((result) => {
-			settled = true;
-			return result;
-		});
-		await vi.advanceTimersByTimeAsync(0);
+
 		expect(fetchMock).toHaveBeenCalledTimes(1);
-
-		await vi.advanceTimersByTimeAsync(10_000);
-		expect(settled).toBe(false);
-
-		await vi.advanceTimersByTimeAsync(10_000);
-		const result = await observedResultPromise;
 		expect(result.stopReason).toBe("error");
-		expect(result.errorMessage).toBe("Codex SSE response headers timed out after 20000ms");
+		expect(result.errorMessage).toBe("Codex SSE response headers timed out after 10ms");
 	});
 
 	it("aborts SSE body reads after response headers arrive", async () => {