[macOS] Model selection does not persist in existing chats; new chats and web work

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

ChatGPT desktop 26.908.70816, build 9275 (bundle: com.openai.codex)

What subscription do you have?

ChatGPT account; app-reported plan type: prolite

What platform is your computer?

Darwin 27.0.0 arm64 arm — macOS 27.0, build 26A428

What issue are you seeing?

Model selection works in new chats in the desktop app, but cannot be changed successfully in existing chats. Existing chats are affected both inside projects and outside projects. Model selection works on the web.

In a recorded example, the model/power selector shows 5.6 Pro, but after the popup closes the message composer still displays 5.6 Instant. The selected option therefore appears not to be retained, or the composer displays an outdated label.

This was initially noticed in existing project conversations, but an existing standalone conversation was subsequently tested and showed the same problem. The scope is existing chats, rather than project membership.

No error message was visible during the recorded model-selection attempt.

What steps can reproduce the bug?

1. Open an existing chat in the ChatGPT desktop app on macOS.
2. Open the model/power selector in the message composer.
3. Select a different mode, such as 5.6 Pro.
4. Close the selector.
5. Observe that the composer still displays 5.6 Instant.
6. Repeat with an existing chat outside a project: the model still cannot be changed successfully.
7. Compare with a new desktop chat, where model selection works, and with the web app, where the reported issue does not occur.

Observed on September 15, 2026.

What is the expected behavior?

Changing the model or reasoning mode in an existing chat should retain the chosen setting, and the selector and composer should display the same choice. The controls should work for existing chats both inside and outside projects, as they do in new chats and on the web.

Additional information

Recording review: the selector displays 5.6 Pro at approximately 19 seconds; after the popup closes, the composer displays 5.6 Instant at approximately 24 seconds. No message is sent during that demonstration, so the recording confirms a UI inconsistency but does not establish which model would execute the next message. Investigation should distinguish a failure to save the setting from a stale display label.

Related report: #43898 describes a similar desktop slider/Instant mismatch on macOS. A shared root cause has not been verified. This report adds the observed distinction between new and existing chats on version 26.908.70816.

The original recording includes unrelated conversation content and is not attached to this public report.

Reproduce the issue on macOS 27.0 with an existing chat, comparing the model selector and composer label in project and standalone conversations against new chats. Trace whether the selection is not persisted or only the display is stale, and compare with related report #43898; done when existing chats retain the selected model or reasoning mode and both controls show the same choice.