Flex tier doesn't work in GPT5 model
Resolved 💬 3 comments Opened Aug 26, 2025 by maker95 Closed Oct 29, 2025
💡 Likely answer: A maintainer (oyiakoumis, contributor)
responded on this thread — see the highlighted reply below.
What version of Codex is running?
_No response_
Which model were you using?
gpt-5
What platform is your computer?
_No response_
What steps can reproduce the bug?
Hi, regarding the commit:
feat: add flex mode option for cost savings (#372)
I believe that now it has a bug since Flex mode should be available for all the Flex enabled models and now gpt-5 is one of this supported models.
The flex tier was introduced but it seems that currently the gpt-5 model is not supported with this Codex CLI implementation.
Also not sure about if this will work with cohesively with reasoning effort parameter. For example what would happen if we enable flex mode and high reasoning effort, are they compatible?
Thanks.
What is the expected behavior?
_No response_
What do you see instead?
_No response_
Additional information
_No response_
3 Comments
Is the flex mode option still valid? I can’t find it anywhere in the codebase, nor is it mentioned in the README or the CLI help.
How do you activate it?
@oyiakoumis In theory it was merged to main, I didn't have personally tested but I have reviewed the commit and the source code and it seems that the GPT 5 model is not in the allowed list (to test in theory, based on the pull request, is running the CLI with --flex-mode: https://github.com/openai/codex/pull/372/files
I'm going to close this in favor of https://github.com/openai/codex/issues/2916, which is a bit broader.