[BUG] .env value overriding model setting

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?

In a nutshell, I use an .env value for anthropic model in the project I am working on with the name of "ANTHROPIC_MODEL". This seems to be the same value that Claude Code uses. As such, every time I load this project in Claude Code it defaults to the model setting in the .env of the project rather than the model I want to use with Claude Code (set though the /model command). Thus, I have to reset this setting every time I launch Claude Code.

What Should Happen?

Claude Code should honor the /model setting and should persist across sessions.

Error Messages/Logs

Steps to Reproduce

1. Have an .env file for project with a value set for "ANTHROPIC_MODEL" (e.g. "claude-sonnet-4-5-20250929")
2. Open project in Claude Code.
3. See that the model selected is the same as the .env value (claude-sonnet-4-5-20250929)
4. Have to manually override this with the /model setting (e.g. Default/Opus 4.5)
5. Close Claude Code
6. Reopen Claude Code, see that the model setting has reverted back to the .env value ("claude-sonnet-4-5-20250929")

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.55

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_