PRODUCTION SCENARIO
After moving a summarization service from Claude Sonnet 4.6 to Claude Opus 5, every request fails with a 400 saying thinking.type.enabled is not supported for this model.
What change keeps extended reasoning working on the new model?
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Answer: Set thinking to type adaptive and control depth with output_config.effort
The documented migration has three parts: remove budget_tokens, set thinking to adaptive, and move depth control to output_config.effort. Switching to adaptive while still steering with budget_tokens fails, because the parameter is removed on these models rather than repurposed. effort nests inside output_config, so a top-level effort field is not the documented control. Keeping budget_tokens as a ceiling alongside the switch still sends a parameter the model rejects.