[BUG] CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1 is being ignored since v2.1.129

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?

On version v2.1.129-v2.1.32 I get the following error, when I try to have a conversation with claude:

API Error: 400 vertex-ai error: Unexpected value(s) `context-1m-2025-08-07` for the `anthropic-beta` 
     header. Please consult our documentation at docs.anthropic.com or try again without the header.   

My settings.json contains:

  "env": {
    [...]
    "CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS": "1"
  },

As far as I understand this should prevent claude from sending the anthrophic-beta header, but it doesn't prevent it anymore. v2.1.128 still works

What Should Happen?

Claude should not send anthropic-beta when environment variable CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1

Error Messages/Logs

API Error: 400 vertex-ai error: Unexpected value(s) `context-1m-2025-08-07` for the `anthropic-beta` 
     header. Please consult our documentation at docs.anthropic.com or try again without the header.

Steps to Reproduce

1. run claude:

$ claude

1. type anything in the interactive terminal

> hi

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.128

Claude Code Version

2.1.132

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

IntelliJ IDEA terminal

Additional Information

_No response_