Windows: built-in image_gen fails after ~308 seconds on complex prompts while ChatGPT web completes

Codex version

• Codex Desktop Store package: 26.715.10079.0
• Desktop client version observed in diagnostics: 26.715.72359
• Codex CLI/runtime: 0.145.0

Subscription

ChatGPT-authenticated Codex session.

Platform

Windows 11 x64.

What issue are you seeing?

The built-in image_gen tool reliably fails for a sufficiently complex image-generation prompt after about five minutes.

Observed timing from a persisted rollout:

• tool call started: 2026-07-23T06:36:16Z
• failure event: 2026-07-23T06:41:25Z
• elapsed: 308.169 seconds

The tool returns:

image generation failed: network error: error sending request for url (https://chatgpt.com/backend-api/codex/images/generations)

No generated image is saved. Less complex image-generation requests can complete, and the same complex image request can complete through ChatGPT web using the same account.

Steps to reproduce

1. Start a fresh Codex Desktop task on Windows.
2. Ask Codex to call the built-in image_gen tool once with a dense prompt, for example:

> Generate a square, photorealistic futuristic Shanghai night market in heavy rain, with dozens of distinct pedestrians, layered Chinese neon shop signs, food stalls, steam, umbrellas, reflective puddles, cables, coherent perspective, cinematic depth, realistic materials, and high detail throughout.

1. Wait for generation.
2. At about 308 seconds, the tool fails with the error above and produces no image.

I reproduced the failure multiple times with complex prompts.

Expected behavior

The image-generation request should remain active until it returns an image, or Codex should use an asynchronous/polling flow that supports image jobs lasting longer than five minutes.

If the backend rejects or expires the job, Codex should surface a specific timeout or backend error rather than the generic network error.

Additional information

This appears related to, but is more deterministic and endpoint-specific than:

• #22089
• #23015
• #23807

Key characteristics:

• built-in standalone image_gen
• /backend-api/codex/images/generations
• reproducible failure at approximately 308 seconds
• simpler image jobs can complete
• the same complex request completes in ChatGPT web