When building AI applications, developers need the freedom to route traffic to the best model for the job without hardcoding endpoints or managing open-source proxies. Google Cloud API Gateway now offers model routing in Public Preview to solve this. It provides a lightweight, serverless ingress layer that accepts OpenAI-compatible requests and dynamically routes them to Gemini, Claude, or OpenAI OSS-GPT.

API Gateway can be used standalone for simple rate limiting and token tracking, or paired seamlessly with the Gemini Enterprise Agent Platform. For example, you can route your agent's egress through Agent Gateway for strict security governance, and then pass the request to API Gateway to handle dynamic routing to Google-hosted LLMs. Here is a step-by-step guide on how to configure your routing logic.

Routing your traffic

Setting up your model routing logic takes just a few steps:

1. Configure your routing rules: You can map virtual model names to specific backend targets directly in your OpenAPI 3.x specification using the new x-google-api-management extension block.

openapi: 3.0.4

info:
  title: OpenAPI 3.x spec using Model Routing
  description: Using Model Routing in an OAS 3.x spec
  version: 1.0.0

x-google-api-management:
  backends:
    gemini-35-flashlite:
      address: >-
        https://aiplatform.googleapis.com/v1/projects/YOUR_PROJECT_ID/locations/global/publishers/google/models/gemini-3.5-flash-lite:generateContent
      deadline: 60.0
      pathTranslation: CONSTANT_ADDRESS

    anthropic-claude-opus-47:
      address: >-
        https://aiplatform.googleapis.com/v1/projects/YOUR_PROJECT_ID/locations/global/publishers/anthropic/models/claude-opus-4-7:rawPredict
      deadline: 60.0
      pathTranslation: CONSTANT_ADDRESS

    openai-gpt-oss-120b:
      address: >-
        https://aiplatform.googleapis.com/v1/projects/YOUR_PROJECT_ID/locations/global/endpoints/openapi/chat/completions
      deadline: 60.0
      pathTranslation: CONSTANT_ADDRESS

  ai:
    models:
      routing:
        routers:
          # Router 1: route between Gemini (default) and Claude.
          gemini-claude-router:
            defaultModel:
              backend: gemini-35-flashlite
              targetModel: google/gemini-3.5-flash-lite
            rules:
              - model: "claude-opus-4-7"
                backend: anthropic-claude-opus-47
                targetModel: anthropic/claude-opus-4-7

          # Router 2: route between OpenAI GPT (default) and Gemini.
          openai-gemini-router:
            defaultModel:
              backend: openai-gpt-oss-120b
              targetModel: openai/gpt-oss-120b-maas
            rules:
              - model: "gemini-3.5-flash-lite"
                backend: gemini-35-flashlite
                targetModel: google/gemini-3.5-flash-lite

servers:
  - url: "https://my-gateway-url.com"

paths:
  /v1/chat/gemini-claude:
    post:
      summary: "Endpoint:defaults to Gemini & Claude as an option."
      operationId: "chatGeminiClaude"
      x-google-model-router: gemini-claude-router
      responses:
        '200':
          description: "OK"

  /v1/chat/openai-gemini:
    post:
      summary: "Endpoint:defaults to OpenAI & Gemini as an option."
      operationId: "chatOpenAIGemini"
      x-google-model-router: openai-gemini-router
      responses:
        '200':
          description: "OK"

YAML

Copied

Note: All backends referenced by a single router must share the same host (for example, aiplatform.googleapis.com). Routing selects a different model and path on that shared Vertex host — it does not route across different hosts.

2. Deploy the Gateway: Deploy your updated API config so the Gateway is active and ready to process traffic.

3. Send standard requests: Your application simply sends a standard OpenAI POST /v1/chat/gemini-claude or POST /v1/chat/openai-gemini request. The Gateway intercepts it, transcodes the payload to the native schema of the backend, and routes it on the fly. As an example (use appropriate values for $API_KEY and my-gateway-url.com) :

curl -X POST "https://my-gateway-url.com/v1/chat/gemini-claude" \
  -H "content-type: application/json" \
  -H "x-api-key: $API_KEY" \
  -d '{
        "model": "claude-opus-4-7",
        "messages": [
          {"role": "user", "content": "Introduce yourself in 5 words"}
        ]
      }'

Shell

Copied

Get started

Model routing is now available in Public Preview for API Gateway. To stop managing proxies and start unifying your AI traffic, check out our documentation to deploy your first model router today.