How to set custom reasoning effort

What is the type of issue?

_No response_

What is the issue?

I want to use codex in headless mode, but couldn't find documentation on how to make the default model gpt-5-high (I am using codex for more complex debugging tasks).

The solution I found is to write the following into ~/.codex/config.toml:

model = "gpt-5"
model_reasoning_effort = "high"

Taken from this github issue's config using o4: https://github.com/openai/codex/issues/1482?utm_source=chatgpt.com.

It would be great if this is documented.

Thank you!

Where did you find it?

https://github.com/openai/codex