fix(vertex): Vertex (Antropic) provider: use .rep.googleapis.com for continental multi-region endpoints (us, eu)

[JPFrancoia]

Issue for this PR

Closes #28348

Closes #27063

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

When using Google Vertex AI with continental multi-region locations (eu, us), the @ai-sdk/google-vertex SDK constructs endpoint URLs like https://eu-aiplatform.googleapis.com.
Unlike standard regional endpoints (e.g. europe-west1-aiplatform.googleapis.com), these continental hostnames do not resolve correctly: they either return 404 or fail to connect, depending on the network environment.

This is a significant issue for enterprise users whose GCP projects provision Anthropic model quota exclusively in continental multi-regions (eu, us) rather than specific regions like europe-west1. In these setups, setting VERTEX_LOCATION=eu is required to reach the quota pool, but the current URL construction makes the endpoint unreachable.

For reference, this is exactly how the Anthropic Python SDK does it: https://github.com/anthropics/anthropic-sdk-python/blob/main/src/anthropic/lib/vertex/_client.py#L125

How did you verify your code works?

I tested the change manually, locally. In my case, my company has a pool of quota for Opus 4.6 in europe-west1, and a pool of quota for Opus 4.7 in "eu". These are the results of my tests:

For the fixed version, run directly from the local codebase:

- GOOGLE_CLOUD_PROJECT=my-fancy-project VERTEX_LOCATION=eu bun dev; opus 4.7 -> works
- GOOGLE_CLOUD_PROJECT=my-fancy-project VERTEX_LOCATION=europe-west1 bun dev; opus 4.6 -> works

The global opencode bin, NOT fixed, installed via brew

- GOOGLE_CLOUD_PROJECT=my-fancy-project VERTEX_LOCATION=europe-west1 opencode; opus 4.6 -> works
- GOOGLE_CLOUD_PROJECT=my-fancy-project VERTEX_LOCATION=eu opencode; opus 4.7 -> doesn't work (expected)

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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[github-actions]

Hey! Your PR title Vertex (Antropic) provider: use .rep.googleapis.com for continental multi-region endpoints (us, eu) doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[rti]

I think this is the required fix. The docs state the same https://docs.cloud.google.com/vertex-ai/generative-ai/docs/partner-models/use-partner-models#eu

[PowerSlime]

Most probably closes #27063 as well

[rti]

Tested successfully with VERTEX_LOCATION=eu

{
  "$schema": "https://opencode.ai/config.json",
  "enabled_providers": [
    "google-vertex-anthropic"
  ],
  "provider": {
    "google-vertex-anthropic": {
      "whitelist": [
        "claude-opus-4-7@default"
      ]
    },
  }
}

Before the patch lands, overwriting baseURL is a possible workaround:

{
  "$schema": "https://opencode.ai/config.json",
  "enabled_providers": [
    "google-vertex-anthropic"
  ],
  "provider": {
    "google-vertex-anthropic": {
      "options": {
        "baseURL": "https://aiplatform.eu.rep.googleapis.com/v1/projects/YOUR-PROJECT-HERE/locations/eu/publishers/anthropic/models/"
      },
      "whitelist": [
        "claude-opus-4-7@default"
      ]
    },
  }
}

[JPFrancoia]

Tested successfully with VERTEX_LOCATION=eu

{
  "$schema": "https://opencode.ai/config.json",
  "enabled_providers": [
    "google-vertex-anthropic"
  ],
  "provider": {
    "google-vertex-anthropic": {
      "whitelist": [
        "claude-opus-4-7@default"
      ]
    },
  }
}

Before the patch lands, overwriting baseURL is a possible workaround:

{
  "$schema": "https://opencode.ai/config.json",
  "enabled_providers": [
    "google-vertex-anthropic"
  ],
  "provider": {
    "google-vertex-anthropic": {
      "options": {
        "baseURL": "https://aiplatform.eu.rep.googleapis.com/v1/projects/YOUR-PROJECT-HERE/locations/eu/publishers/anthropic/models/"
      },
      "whitelist": [
        "claude-opus-4-7@default"
      ]
    },
  }
}

Correct, that's the workaround I'm using too.

[rekram1-node]

will review today

[rekram1-node]

This is a legacy provider u should not use if u can help it, instead just use google-vertex it should work for other models and anthropic models just fine

[rekram1-node]

it will be deprecated in an upcoming release

[rekram1-node]

/review

[rekram1-node]

/review

[rekram1-node]

made a small change to make sure it should work for google-vertex too when using anthropic models