ClaudeCodeChanges

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Claude docs changes for April 7th, 2026 [diff]

Executive Summary

  • max effort level is now available on Claude Sonnet 4.6 (previously restricted to Opus 4.6 only)
  • Prefilling is no longer described as "deprecated" — it now explicitly returns a 400 error on Opus 4.6 and Sonnet 4.6, and Claude Sonnet 4.5 is no longer listed as a restricted model
  • The llms-full.txt resource link has been removed from the API resources overview

API changes

Changed documents

Adaptive Thinking [Source]

  • The max effort level is now available on Claude Sonnet 4.6 in addition to Opus 4.6 (previously stated as Opus 4.6 only). [line 63] [Source]

Effort [Source]

  • The max effort level is now available on Claude Sonnet 4.6 in addition to Opus 4.6 (previously stated as Opus 4.6 only). [line 34] [Source]
  • Added a bullet point for max effort in the Sonnet 4.6 usage guidance section. [line 48] [Source]
  • Updated guidance on when to use max effort to reflect its availability on Sonnet 4.6. [line 74] [Source]

Increase Consistency [Source]

  • Prefilling note updated: no longer described as "deprecated". Claude Sonnet 4.5 removed from the list of models that don't support prefilling. [line 21] [Source]

Overview [Source]

  • The llms-full.txt link (complete LLM-optimized documentation) has been removed from the resources overview. [line 51] [Source]

Reduce Prompt Leak [Source]

  • Prefilling note updated: no longer described as "deprecated". Claude Sonnet 4.5 removed from the list of models that don't support prefilling. [line 20] [Source]

Working with Messages [Source]

  • Prefilling clarified: no longer described as "deprecated" — now explicitly stated to return a 400 error on Opus 4.6 and Sonnet 4.6. Claude Sonnet 4.5 removed from the list of affected models. A link to the migration guide was added. [line 145] [Source]