Adaptive Thinking Official Documentation

Description

Official Anthropic documentation (platform.claude.com/docs/en/build-with-claude/adaptive-thinking) published after the HackerNews regression thread. Confirms design: Claude Opus 4.6 and Sonnet 4.6 use adaptive thinking as default; Mythos Preview has adaptive thinking always-on with no opt-out (effort is unset and model auto-applies). Adaptive thinking is SUPPOSED to allocate zero reasoning on simple turns — the bug is it allocates zero on turns involving 3rd-party API versions, exact hashes, package names where hallucination risk is high. CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING=1 switches to fixed effort=high (pre-February behavior).

Key claims

Relations

Sources

src-20260409-370f03f56802