Codex CLI 0.146.0: /backend-api/codex/responses/compact returns 404 {"detail":"Not Found"}

What version of Codex CLI is running?

0.146.0

What subscription do you have?

pro 20x

Which model were you using?

gpt-5.6-sol

What platform is your computer?

macOS

What terminal emulator and version are you using (if applicable)?

No response

Codex doctor report

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}

What issue are you seeing?

■ Error running remote compact task: unexpected status 404 Not Found: {"detail":"Not Found"}, url: https://chatgpt.com/backend-api/codex/responses/compact, cf-ray: a2a5f3a0dd12a5bb-BOS,
request id: 149cd99d-fab9-4e76-a94a-6cbbf0d6a5a9

What steps can reproduce the bug?

I consistently encounter this issue whenever Codex CLI attempts to compact the conversation context.

There are several ways to reproduce it:

1. Automatic compaction

   • Continue using a Codex CLI session until the context window approaches its limit.
   • When Codex automatically triggers context compaction, the compaction request fails with the following error:

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

2. Manual /compact in a long-running session

   • Run /compact manually in an existing session.
   • The same 404 Not Found error is returned.

3. Manual /compact in a brand-new session

   • Start a completely new Codex CLI session.
   • Have only a short conversation, with context usage at approximately 1%.
   • Run /compact manually.
   • The exact same 404 Not Found error still occurs.

Therefore, the issue does not appear to depend on the amount of context being used or whether the context window is actually close to its limit.

Both automatic compaction and manually invoking /compact consistently fail because the request to:

https://chatgpt.com/backend-api/codex/responses/compact

returns:

{"detail":"Not Found"}

This makes context compaction effectively unavailable in Codex CLI. In long-running sessions, once the context reaches the automatic compaction threshold, I can no longer continue the session normally because the compaction step fails.

What is the expected behavior?

No response

Additional information

No response

Start by reproducing the 404 with Codex CLI 0.146.0 and inspect the handling of the /backend-api/codex/responses/compact request, including the remote_compaction_v2=false configuration. The payload names no source files or tests; done means establishing why the endpoint is unavailable and verifying that the CLI no longer encounters this 404.