400 role: system is not supported on this model with claude-opus-4-7 via claude.ai auth

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?

Every time I type a prompt into the terminal, it thinks for 0 seconds and immediately returns back "API Error: 400 role 'system' is not supported on this model". I am using Opus 4.7. This happens on all efforts. Sonnet works perfectly fine.

What Should Happen?

Claude should return whatever I asked.

Error Messages/Logs

API Error: 400 role 'system' is not supported on this model

Steps to Reproduce

Steps to reproduce:

1. Authenticate via claude.ai (no ANTHROPIC_API_KEY set)
2. /model → select Opus 4.7 (any effort level)
3. Send any message

Expected: Normal response

Actual: API error 400: role: system is not supported on this model

Works fine with: Sonnet 4.6 (same auth, same setup)

Version: 2.1.146

OS: Windows 11 Pro

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.146

Platform

Other

Operating System

Windows

Terminal/Shell

Other

Additional Information

Using Git Bash claude code.