Codex Desktop unusable: "Selected model is at capacity" for all models on my account

What version of the Codex App are you using (From “About Codex” dialog)?

Version 26.814.41407

What subscription do you have?

ChatGPT Pro 20x

What platform is your computer?

Darwin 25.5.0 arm64 arm

What issue are you seeing?

I am unable to use Codex Desktop on my account.

Codex consistently returns:

"Selected model is at capacity. Please try a different model."

The issue happens for:

• Every conversation
• Every prompt, including simple prompts like "hi"
• Every available model, except GPT-5.4 Mini and GPT-5.3 Codex Spark
• Different reasoning effort settings

Models tested:

• GPT-5.6 Terra
• GPT-5.6 Luna
• GPT-5.5
• GPT-5.4

The error still occurs after switching models.

Important observations:

• ChatGPT works normally with the same account.
• The same account has the same issue on another computer.
• Another user's account works normally on the same computer.
• GPT-5.3-codex-spark worked for one conversation turn, then failed with the same error.

Sometimes Codex starts processing successfully (for example, web search starts), but the final response is replaced by the capacity error.

This looks like an account-specific Codex routing/admission issue rather than a temporary model capacity problem.

What steps can reproduce the bug?

1. Open Codex Desktop.
2. Sign in with my ChatGPT Pro account.
3. Start a new conversation.
4. Select any available model.
5. Send any prompt (even "hi").
6. Wait for response.
7. The request fails with:

"Selected model is at capacity. Please try a different model."

1. Switching to another model produces the same result.

The issue reproduces consistently across different machines.

What is the expected behavior?

Codex should process the request normally using the selected model.

Changing between available models should allow the request to continue when one model has capacity issues.

Additional information

I have already tested:

• Different Codex models
• Different conversations
• Different prompts
• Different machines

The issue appears isolated to my account because:

• My account fails on multiple devices.
• Other accounts work on the same device.

The same issue happens when I use Chatgpt desktop and Codex cli

Please investigate:

• Account entitlement/status
• Codex backend routing
• Model admission control
• Possible account-level throttling or corrupted state

Screenshot attached showing the repeated error across multiple models.

<img width="787" height="1270" alt="Image" src="https://github.com/user-attachments/assets/eadb144e-7fe8-4483-a051-39ede50bee93" />