[Bug] Claude Opus model output capped at 64000 tokens

Bug Description
Caps Opus 4.6 max output tokens is capped

Environment Info

• Platform: darwin
• Terminal: tmux
• Version: 2.1.37
• Feedback ID: d4c60efa-050c-434f-9cf3-e00f99b499a4

If you run claude doctor, you'll see:

 Environment Variables
 └ CLAUDE_CODE_MAX_OUTPUT_TOKENS: Capped from 127999 to 64000

<img width="832" height="104" alt="Image" src="https://github.com/user-attachments/assets/101583f1-1db6-4511-8222-d6c2d0a92598" />

According to the 4.6 announcement, 128k output tokens is supported
https://www.anthropic.com/news/claude-opus-4-6