[BUG] Support eu multi-region via Vertex

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?

Two days ago, Google announced support for multi-region endpoints (us and eu) for Claude models via Vertex. Except for the global endpoint, Opus 4.7 is now only available through these multi-region endpoints (regional endpoints are no longer supported).

Setting CLOUD_ML_REGION to eu doesn’t work—Claude returns the following error:

The model claude-opus-4-7 is not available on your vertex deployment. Try /model to switch to claude-opus-4-1@20250805, or ask your admin to enable this model.

It seems that the URLs for multi-region endpoints are quite different from regional endpoints:

• Multi-regional: "https://aiplatform.us.rep.googleapis.com/v1/projects/${PROJECT_ID}/locations/us/publishers/anthropic/models/${MODEL_ID}:rawPredict"
• Regional : "https://us-east5-aiplatform.googleapis.com/v1/projects/${PROJECT_ID}/locations/us-east5/publishers/anthropic/models/${MODEL_ID}:${METHOD}"

What Should Happen?

Claude code should response, using multi-region endpoint

Error Messages/Logs

> The model claude-opus-4-7 is not available on your vertex deployment. Try /model to switch to claude-opus-4-1@20250805, or ask your admin to enable this model.

Steps to Reproduce

1. Install Claude Code (latest version)
2. Setup Claude Code to use vertex with regional endpoint and opus-4-7

export CLAUDE_CODE_USE_VERTEX=1
export CLOUD_ML_REGION=eu
export ANTHROPIC_VERTEX_PROJECT_ID=YOUR-PROJECT-ID
export ANTHROPIC_DEFAULT_OPUS_MODEL='claude-opus-4-7'

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.112

Platform

Google Vertex AI

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_