AI EngineerGuide

Tool calling on GPT-6 Astra, GPT-6.1 Sol and GPT-6.1 Terra requires the Responses API

Rejected Applies to gpt-6-astra, gpt-6.1-sol, gpt-6.1-terra on the OpenAI Chat Completions.

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

How to fix it

Move the request to POST /v1/responses. This changes the request and response shape, so it isn’t auto-fixed.

Before
{
  "messages": [
    {
      "content": "Summarize this ticket.",
      "role": "user"
    }
  ],
  "model": "gpt-4o-2024-08-06",
  "tools": [
    {
      "function": {
        "name": "get_invoice",
        "parameters": {
          "properties": {
            "id": {
              "type": "string"
            }
          },
          "required": [
            "id"
          ],
          "type": "object"
        }
      },
      "type": "function"
    }
  ]
}
After (GPT-6 Astra)
{
  "messages": [
    {
      "content": "Summarize this ticket.",
      "role": "user"
    }
  ],
  "model": "gpt-6-astra"
}
Check your whole request in the linter

Official source

GPT-6 Astra, GPT-6.1 Sol, and GPT-6.1 Terra support Chat Completions, but tool calling requires Responses.

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-astra, gpt-6.1-sol, gpt-6.1-terra?

Move the request to POST /v1/responses. This changes the request and response shape, so it isn’t auto-fixed.

Where is this documented?

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