[BUG] Frequent premature compaction + infinite loop + prompt freezing with Opus 4.6 on 1M context

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 Code Version: 2.1.89
Model: claude-opus-4-6 (1M context)
OS: Debian 6.1.164-1
Platform: CLI

Bug Description:
Conversation is being compacted every 5–10 minutes despite context window never exceeding ~100K tokens. This has been ongoing for 1+ hour. The session is also unusually slow, and the prompt randomly freezes requiring Esc to unblock.

Expected Behavior:
Compaction should only trigger when approaching the context limit, not at <10% usage.

Actual Behavior:

• Compaction triggers every 5–10 minutes at low token usage (~100K / 1M)
• Session is significantly slower than normal
• Prompt occasionally freezes and requires Esc + Enter to recover
• Behavior consistent with the infinite compaction loop reported in #6004, #4878

Steps to Reproduce:

1. Start Claude Code with claude-opus-4-6 on 1M context
2. Begin a multi-file coding session
3. Observe repeated compaction at low token usage within minutes

What Should Happen?

Conversation compaction should only trigger when the context window is close to its limit (e.g., 90–95% of the 1M token budget). With a 1M context window and only ~100K tokens used, compaction should not occur at all. The session should remain responsive, and the prompt should never freeze or require manual interruption (Esc) to recover.

Error Messages/Logs

Steps to Reproduce

Steps to Reproduce:

1. Start Claude Code with claude-opus-4-6 on 1M context
2. Begin a multi-file coding session
3. Observe repeated compaction at low token usage within minutes

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.89

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Windows Terminal

Additional Information

_No response_