Anthropic 400 on the thinking parameter right after a model upgrade: enabled vs adaptive depends on the generation

400 on thinking config after a model swap: use the right mode

Symptom

The thinking parameter worked on the old model and returns 400 invalid_request_error on the new one, with no other change.

Confirm the cause

• Claude 4.7 and later removed extended thinking: thinking with type enabled is rejected.
• Claude 4.5 and earlier only support extended thinking: thinking with type adaptive is rejected.

Match the generation: if you moved forward, migrate; if you moved back, restore the old parameter.

Fix

1. On 4.7 and later: drop budget_tokens, set thinking type to adaptive, and control depth with output_config effort instead of a token budget.
2. On 4.5 and earlier: use thinking type enabled with budget_tokens (minimum 1024).
3. Remove the interleaved-thinking-2025-05-14 beta header after migrating to adaptive: adaptive interleaves automatically.

Verify

The same request shape succeeds on the target model. Note the first request after any mode switch invalidates cache breakpoints once, then caching resumes.

Extended thinking not supported (4.7+) and adaptive thinking not supported (4.5 and earlier), with the migration mapping, are documented on the errors page and the extended thinking page. Verified live at https://docs.anthropic.com/en/api/errors and https://docs.anthropic.com/en/docs/build-with-claude/extended-thinking.