[BUG] Version 2.1.70 has a very low cache hit rate

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?

<img width="1694" height="526" alt="Image" src="https://github.com/user-attachments/assets/4193c789-1e39-40f5-90b2-6286a6137bc1" />
My local tool's detection is based on the calculations returned by the API. (See diagram)

What Should Happen?

I previously found that version 2.1.63 had a very high cache hit rate, consistently maintaining over 90%.

Error Messages/Logs

Steps to Reproduce

This can be obtained from the interface return value; the amount of "read" is decreasing significantly.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.63

Claude Code Version

2.1.70

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_