[BUG] getting prompt is too long after just 130 messages,

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?

getting prompt is too long after just 130 messages,

If I try to compact, getting this error

Error: Error during compaction: Error: Conversation too long. Press esc twice to go up a few messages and try again.

This never happened before, very frustrating

What Should Happen?

One issue analysis may take long, explaining the context, in the middle of something if suddenly starts throwing error "Prompt is too long" then I will be stuck nowhere in between production issues.

Error Messages/Logs

Steps to Reproduce

1. creating an implementation.md file
2. executing the plan
3. testing for bugs
4. in the middle of nowhere suddenly the context window is gone, it starts throwing "Prompt is too long"

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Opus 4.5

Claude Code Version

Opus 4.6

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_