[BUG] Git commit co-author shows incorrect model name (Opus 4.6 instead of Sonnet 4.5)

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?

When Claude Code creates git commits, the co-author line incorrectly shows "Claude Opus 4.6" even when the
actual model being used is Claude Sonnet 4.5.

What Should Happen?

The commit message should end with:
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Or generically:
Co-Authored-By: Claude Code <noreply@anthropic.com>

Error Messages/Logs

Steps to Reproduce

1. Use Claude Code (powered by Sonnet 4.5) to create a git commit
2. Check the commit message

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.32 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

This appears to be a hardcoded value in the Bash tool's system instructions for git commits, likely left over
from when Opus 4.6 was the default model. The co-author line should match the actual model being used, or
use a generic "Claude Code" identifier.