We use Vertex AI at work for accessing Anthropic’s models and the opencode setup is quite smooth! Although getting your authentication credentials from Google can be a little tricky, using them with opencode involves setting a few environment variables.

Setting up Vertex AI#

Before you point opencode at Vertex AI, you need a few things on the GCP side.

Prerequisites#

A GCP project with the Vertex AI API enabled
IAM permissions for the Claude models (your account needs the aiplatform.endpoints.predict permission, or a broader role like Vertex AI User)
Either a service account key or Application Default Credentials (ADC)

Authentication#

You have two main options here. The easiest for local development is ADC:

gcloud auth application-default login

This stores credentials locally and opencode picks them up automatically.

If you’re using a service account (common in enterprise setups where your org provisions access), point to the key file:

export GOOGLE_APPLICATION_CREDENTIALS=/path/to/your-service-account.json

Environment variables#

Set these in your shell profile or session:

export ANTHROPIC_VERTEX_PROJECT_ID=your-gcp-project-id
export GOOGLE_CLOUD_PROJECT=your-gcp-project-id
export GOOGLE_APPLICATION_CREDENTIALS=/path/to/your-service-account.json  # if not using ADC

You can also set VERTEX_LOCATION if you need a specific region, but the global endpoint is the default. It routes to the nearest available region.

Using opencode#

You don’t need to configure opencode at all! It finds the environment variables and takes care of the rest for you.

You can type /models, press enter, and you should see the list of available models from Vertex AI. From there, use CTRL-F to select any favorites that you use often.

Troubleshooting#

If you don’t see any models, double check the environment variables to ensure they are set in your terminal session. You may need to open a new terminal or source your shell profile to pick up the new variables.

You can also run opencode models --refresh to force a refresh of the model list from Vertex AI.

Using Anthropic’s models via Vertex AI in opencode