[BUG] API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0.thinking.signature: Field required"},"request_id":"req_011CYFMQMVeUFaeJoMHGWQHP"}

Preflight Checklist

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

What's Wrong?

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0.thinking.signature: Field required"},"request_id":"req_011CYFMQMVeUFaeJoMHGWQHP"}

What Should Happen?

it should work!

Error Messages/Logs

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0.thinking.signature: Field required"},"request_id":"req_011CYFMQMVeUFaeJoMHGWQHP"}

Steps to Reproduce

try to write anything you want

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.45 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_