Claude's reasoning capabilities have evolved significantly. Opus 4.6 and Sonnet 4.6 introduced Extended Thinking with explicit budget_tokens. However, Opus 4.7 (April 2026) fundamentally changed this — replacing explicit thinking budgets with Adaptive Thinking.
thinking: {"type": "enabled", "budget_tokens": N} returns a 400 error on Opus 4.7. You MUST use thinking: {"type": "adaptive"} instead. Adaptive thinking outperforms the old explicit budgets on all benchmarks.On pre-4.7 models, you set budget_tokens (minimum 1024). These tokens are consumed from your max_tokens limit. If you set max_tokens: 4096 and budget_tokens: 2048, the model has exactly 2048 tokens left for its response.
With adaptive thinking, the model dynamically decides how much to reason based on task complexity. Simple questions get instant answers; complex coding tasks trigger deep multi-step reasoning. You control intensity via the effort parameter instead of raw token counts.
Claude can perform interleaved thinking — reasoning in between sequential tool calls. This allows the model to analyze tool outputs, adjust its strategy, and deliberate before making the next action. Critical for complex multi-step agent workflows.
In Opus 4.7, thinking content is hidden by default in API responses. You must explicitly set thinking: {"type": "adaptive", "visible": true} to see the reasoning chain. This change improves response cleanliness for production applications.