AI EngineerGuide

Remove temperature, top_p and logprobs on GPT-6 unless reasoning effort is none

Rejected Applies to gpt-6* on the OpenAI Chat Completions and OpenAI Responses API.

OpenAI's docs describe this error but don't quote the exact message, so we don't either.

How to fix it

Remove temperature, top_p and top_logprobs (and logprobs on Chat Completions), or set reasoning effort to none where the model supports it.

Before
{
  "logprobs": true,
  "messages": [
    {
      "content": "Summarize this ticket.",
      "role": "user"
    }
  ],
  "model": "gpt-4o-2024-08-06",
  "temperature": 0.2
}
After (GPT-6 Luna)
{
  "messages": [
    {
      "content": "Summarize this ticket.",
      "role": "user"
    }
  ],
  "model": "gpt-6-luna"
}
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Official source

When reasoning effort is not none, remove temperature, top_p, and top_logprobs. For Chat Completions, also remove logprobs.

https://developers.openai.com/api/docs/guides/latest-model (last checked 2026-11-02)

Other changes for the same models

All migration errors

FAQ

How do I fix this when moving to gpt-6*?

Remove temperature, top_p and top_logprobs (and logprobs on Chat Completions), or set reasoning effort to none where the model supports it.

Where is this documented?

In OpenAI’s official docs: https://developers.openai.com/api/docs/guides/latest-model, last checked 2026-11-02.