thinking type disabled returns a 400 on Claude Sonnet 5.5

Error message, quoted from Anthropic's docs:

To turn thinking off on this model, send "thinking": {"type": "between_tools"} instead of {"type": "disabled"}. The model does not think before responding. The short updates it writes between tool calls come back as thinking blocks.

How to fix it

Send thinking: {"type": "between_tools"} at low, medium or high effort. At xhigh or max, use adaptive thinking instead.

{
  "max_tokens": 1024,
  "messages": [
    {
      "content": "Summarize this ticket.",
      "role": "user"
    }
  ],
  "model": "claude-sonnet-4-5-20250929",
  "thinking": {
    "type": "disabled"
  }
}

{
  "max_tokens": 1024,
  "messages": [
    {
      "content": "Summarize this ticket.",
      "role": "user"
    }
  ],
  "model": "claude-sonnet-5-5",
  "thinking": {
    "type": "between_tools"
  }
}