[MODEL] 1M Opus still degrades around 150k context

Preflight Checklist

• [x] I have searched existing issues for similar behavior reports
• [x] This report does NOT contain sensitive information (API keys, passwords, etc.)

Type of Behavior Issue

Other unexpected behavior

What You Asked Claude to Do

It's hard to explain the context, I was asking claude to write some yaml.

What Claude Actually Did

Started adding interpretive layers, not what I asked for.

Expected Behavior

Stuck to what I had asked.

Files Affected

Permission Mode

Accept Edits was ON (auto-accepting changes)

Can You Reproduce This?

Sometimes (intermittent)

Steps to Reproduce

Add 160k of context. Ask it to start writing YAML. It gets ideas.

Claude Model

Opus

Relevant Conversation

Impact

Low - Minor inconvenience

Claude Code Version

2.1.76

Platform

Anthropic API

Additional Context

This is about the same point where I run into this problem typically with Opus. 1m is a larger context window, I expect the degradation point to be higher.