[BUG] When open claude code with --system-prompt, the model will be wrong.

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?

I am using the latest claude version, which is v2.0.34.
When I add a --system-prompt when using claude, it will be use claude 3.5 by default. But if I didn't give the param, the model will be right.

What Should Happen?

<img width="1688" height="598" alt="Image" src="https://github.com/user-attachments/assets/d6f2f54b-12cc-4e4b-a833-6f74e67af247" />

Error Messages/Logs

Steps to Reproduce

1、claude --model claude-sonnet-4-5 --system-prompt "Please answer to the user honestly." "What's your claude version?"
2、claude --model claude-sonnet-4-5 "What's your claude version?"

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.34

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_