Codex Desktop context compaction fails with /responses/compact 404 on Windows

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

26.506.3741.0

What subscription do you have?

ChatGPT Plus

What platform is your computer?

_No response_

What issue are you seeing?

Codex Desktop works normally until the conversation reaches the automatic context compaction threshold.

When context compaction is triggered, the UI displays:

“Context automatically compacted”

Immediately afterwards, Codex returns:

Error running remote compact task: unexpected status 404 Not Found
url: https://chatgpt.com/backend-api/codex/responses/compact

After this happens, the conversation cannot continue normally. Sending another message causes the same remote compact 404 error again.

I have reproduced this issue in multiple newly-created Codex Desktop conversations.

Environment:

• Windows 11 x64
• ChatGPT Plus
• Codex Desktop: latest available version
• Model: GPT-5.5
• Reasoning level tested: High / Extra High
• Codex CLI installed separately: 0.147.0

The problem occurs specifically when automatic context compaction is triggered.

What steps can reproduce the bug?

1. Open Codex Desktop on Windows.
2. Start a new conversation using GPT-5.5.
3. Work normally in the conversation and let the context grow.
4. Continue until Codex automatically triggers context compaction.
5. The UI displays “Context automatically compacted”.
6. The request to /backend-api/codex/responses/compact returns HTTP 404.
7. Send another message in the same conversation.
8. Codex attempts context compaction again and returns the same 404 error.

This has been reproduced in multiple newly-created conversations, not just one old or unusually long thread.

What is the expected behavior?

_No response_

Additional information

_No response_