thinking type enabled with budget_tokens returns a 400 on Claude Sonnet 5.5
Returns 400
Applies to claude-sonnet-5-5 on the Anthropic Messages API.
Error message, quoted from Anthropic's docs:
"thinking.type.enabled" is not supported for this model. Use "thinking.type.adaptive" and "output_config.effort" to control thinking behavior.How to fix it
Remove the budget and set an effort level in output_config.effort. There’s no fixed mapping from budget to effort, so evaluate at two or three levels.
{
"max_tokens": 16000,
"messages": [
{
"content": "Summarize this ticket.",
"role": "user"
}
],
"model": "claude-sonnet-4-5-20250929",
"thinking": {
"budget_tokens": 8000,
"type": "enabled"
}
}{
"max_tokens": 16000,
"messages": [
{
"content": "Summarize this ticket.",
"role": "user"
}
],
"model": "claude-sonnet-5-5",
"output_config": {
"effort": "high"
},
"thinking": {
"type": "adaptive"
}
}Official source
Thinking budgets return an error.
https://platform.claude.com/docs/en/models/sonnet-5-5/migration-guide#sonnet-46-breaking-changes (last checked 2026-11-02)
Other changes for the same models
- temperature, top_p and top_k return an error on Claude Sonnet 5.5
- Assistant message prefill returns a 400 on Claude Sonnet 5.5
- tool_choice any or tool returns a 400 on Claude Sonnet 5.5
- thinking type disabled returns a 400 on Claude Sonnet 5.5
- Top-level output_format returns a 400 on Claude Sonnet 5.5
- computer_20250124 isn’t accepted by Claude Sonnet 5.5 or Haiku 5.5
- fine-grained-tool-streaming-2025-05-14 with a toolset returns a 400
- Beta headers to remove when moving to Claude Sonnet 5.5
- Claude Sonnet 5.5 thinks by default when thinking is omitted
FAQ
What does ""thinking.type.enabled" is not supported for this model. Use "thinking.type.adaptive" and "output_config.effort" to control thinking behavior." mean?
thinking type enabled with budget_tokens returns a 400 on Claude Sonnet 5.5 The fix: Remove the budget and set an effort level in output_config.effort. There’s no fixed mapping from budget to effort, so evaluate at two or three levels.
How do I fix this when moving to claude-sonnet-5-5?
Remove the budget and set an effort level in output_config.effort. There’s no fixed mapping from budget to effort, so evaluate at two or three levels.
Where is this documented?
In Anthropic’s official docs: https://platform.claude.com/docs/en/models/sonnet-5-5/migration-guide#sonnet-46-breaking-changes, last checked 2026-11-02.