One API Gateway for GPT, Claude, and Gemini: How It Works

Why You Need a Gateway

Your app works with OpenAI today, but next quarter you want to test Claude, and someone mentions Gemini. Each provider has its own SDK, auth, error format, and rate limits. A gateway sits between your app and the providers, normalizing everything.

How It Works

You send a standard chat completion request to your gateway endpoint. The gateway routes it to the right provider based on the model name you specify, translates the request format, and returns a consistent response. Your code never knows if it's talking to OpenAI or Anthropic.

What You Get

One API key, one base URL, one set of logs. Switching from gpt-4o to claude-sonnet is just changing the model name in your request. You can also set up fallbacks: if OpenAI has an outage, the gateway automatically retries on another provider.

Self-Hosted vs Managed

Managed gateways (like OpenRouter or Portkey) handle the providers for you — you pay one bill. Self-hosted gateways (like LiteLLM) give you full control but require you to manage provider keys and uptime. For most teams, managed is the faster start.

The Catch

Provider-specific features — function calling formats, extended thinking, vision details — don't always map cleanly. The abstraction covers the 80% common case; for the rest, you'll need provider-specific calls. Build the escape hatch into your code from day one.