Vertex AI: Route Agents to Claude & Gemini on GCP

Route agent requests to Vertex AI models on Google Cloud, including Claude and Gemini. Supports service account and ADC authentication.

Overview

OneCLI connects AI agents to Google Cloud’s Vertex AI platform. Agents can call models hosted on Vertex AI, including Claude (via Anthropic’s Model Garden) and Gemini. The gateway injects Google Cloud credentials into requests to the Vertex AI API automatically.

This is useful for agents that need to call AI models through your own Google Cloud project, using your billing and quotas.

Setup

1. Prepare your credentials

   You need one of the following:

   • Service account key: Create a service account in the Google Cloud console with the Vertex AI User role. Download the JSON key file.
   • Authorized user credentials: Run gcloud auth application-default login on your machine and use the generated credentials file.
2. Connect in OneCLI

   Open the OneCLI dashboard, go to Connections > Vertex AI, and provide:

   • Credentials: paste the JSON key or upload the credentials file
   • Project ID: your Google Cloud project ID
   • Region: the Vertex AI region (e.g., us-central1)

   

   The Vertex AI connect window in OneCLI.

What agents can do

• Send prompts to Claude models hosted on Vertex AI (Claude Sonnet, Claude Haiku, Claude Opus)
• Send prompts to Gemini models
• Use streaming or non-streaming inference
• Pass structured messages with text and image inputs
• Call models with tool/function calling enabled
• Access any model available in your project’s Model Garden
• Run batch prediction jobs

Controlling access

Access is per agent: grant the connection to each agent that needs it, choosing per tool what runs freely, what needs human approval, and what stays blocked — a read-only agent is a single grant. Organization rules add guardrails on top, like rate limits and blanket blocks. Everything is checked before credential injection, so a blocked request never reaches Vertex AI.

Using with MCP servers

If your agent uses an MCP server that needs Vertex AI credentials locally, see the Vertex AI credential stubs guide to set up placeholder files that the gateway fills in at request time.