[BUG] Claude code quality (Opus 4.6) has degraded

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?

Quality has been significantly degraded in the last week, including

• Reduced effort - claude not investigating issues thoroughly to completeness with the same system prompts, skills, plugins, and tools
• Factual inaccuracies - asking for analyses produces hallucinated outputs not reflected in the code
• Gaslighting - not taking responsibility for mistakes and blaming me

What Should Happen?

Un-quantize Opus 4.6

Error Messages/Logs

Steps to Reproduce

1. Open claude code with a complex code base
2. try to give any task
3. notice the lower quality results than what we were experiencing 2+weeks ago

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.92

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_