[BUG] Context low; triggered much too early in claude-sonnet-4-5-20250929[1m].

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?

claude-sonnet-4-5-20250929[1m] reaches the context far too quickly and prompts for /compact.

<img width="765" height="273" alt="Image" src="https://github.com/user-attachments/assets/49f1de8d-111e-482b-b8f1-a61805a5f974" />

What Should Happen?

That the request to /compact only comes when nearly 1000k tokens have been reached.

Error Messages/Logs

Steps to Reproduce

1. Select claude-sonnet-4-5-20250929[1m]
2. Start coding
3. Context low is displayed after a while (sometimes 27%, sometimes 25%, sometimes 29%)

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.42 (Claude Code)

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

Other

Additional Information

<img width="610" height="761" alt="Image" src="https://github.com/user-attachments/assets/3680e590-8449-4222-ab91-ff6ccd9c241b" />

<img width="555" height="744" alt="Image" src="https://github.com/user-attachments/assets/3f784a19-ddfe-429a-a7af-31e3a7bf3c1a" />