[BUG] max_tokens: 64001 > 64000 error on Opus 4.5 - broken since v2.1.9

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?

With any prompt even if it's just a "Hi" i get this error showing in the screenshot, I went through all my files to check if i missed up with the max output tokens, i even try to hard code it to 64000, but looks like a bug happening by incremting the max token output by one always, I think this happened when i tried to prompt with "ultrathink" and saw a tip that ultrathink have no effect now etc .. finally i love you guys and all the excellence u deliver.

<img width="1484" height="185" alt="Image" src="https://github.com/user-attachments/assets/f0f4648e-2f22-4955-8937-1ea31f8d9fcc" />

What Should Happen?

Max token output controlled by the cli it self since it have a built in limit.

Error Messages/Logs

Steps to Reproduce

With any prompt even if it's just a "Hi" i get this error showing in the screenshot, I went through all my files to check if i missed up with the max output tokens, i even try to hard code it to 64000, but looks like a bug happening by incremting the max token output by one always, I think this happened when i tried to prompt with "ultrathink" and saw a tip that ultrathink have no effect now etc .. finally i love you guys and all the excellence u deliver.

<img width="1484" height="185" alt="Image" src="https://github.com/user-attachments/assets/f0f4648e-2f22-4955-8937-1ea31f8d9fcc" />

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.9

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Warp

Additional Information

_No response_