claude-code - 💡(How to fix) Fix [BUG] API Error 400: thinking blocks must remain as original response - claude-opus-4-8 incompatibility

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Error Message

API returns 400 error on thinking/redacted_thinking block handling.

Error Messages/Logs

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Preflight Checklist

  • I have searched existing issues and this hasn't been reported yet
  • This is a single bug report (please file separate reports for different bugs)
  • I am using the latest version of Claude Code

What's Wrong?

API returns 400 error on thinking/redacted_thinking block handling. Claude Code appears to be modifying or not preserving thinking blocks correctly when sending them back in subsequent API calls.

What Should Happen?

Opus 4.8 should work without errors, same as Sonnet 4.6.

Error Messages/Logs

Steps to Reproduce

Opus 4.8 should work without errors, same as Sonnet 4.6.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

No response

Claude Code Version

2.1.156

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

No response

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claude-code - 💡(How to fix) Fix [BUG] API Error 400: thinking blocks must remain as original response - claude-opus-4-8 incompatibility