Feature Request: Support Models API for Vertex AI client

[yanmxa]

Problem

When using the Vertex AI client with vertex.WithGoogleAuth(), the Models API (client.Models.ListAutoPaging()) does not work.

The Vertex middleware in vertex/vertex.go only handles:

• /v1/messages
• /v1/messages/count_tokens

But /v1/models is not processed, causing requests to fail.

Expected

Either:

1. Support /v1/models endpoint translation for Vertex AI
2. Provide a helper like vertex.AvailableModels() returning known Vertex model IDs
3. Document this limitation with available model IDs

Use Case

Building a model selector UI that needs to dynamically list available models when using Vertex AI.

Environment

• anthropic-sdk-go v1.19.0+
• Using vertex.WithGoogleAuth()