What Is an LLM Gateway? The Missing Layer Between Your App and AI Models

Most AI apps don’t stay simple for very long. At the beginning, a single AI model is enough. But as the app grows, one model may become too expensive for high-volume requests, a new model could perform better for reasoning tasks, and your primary provider may start enforcing aggressive rate limits during peak traffic. Suddenly, your app needs to depend on multiple AI models, different response formats, separate billing systems, and a growing pile of logic just to keep requests flowing reliably. That’s the standard trajectory for any AI application that makes it past the prototype stage. At OpenRouter, we operate one of the largest LLM gateway platforms in production, routing billions of requests and trillions of tokens every week across hundreds of models and dozens of providers. This article explains what an LLM gateway is, what it actually does in production, how to evaluate one, and where the major options genuinely differ. Use the direct Application Programming Interface (API) if you only call one model from one provider. Use OpenRouter if you want the fastest path to multi-provider routing without managing infrastructure. Use LiteLLM if self-hosting, infrastructure ownership, and deep customization matter more than operational simplicity. Use Portkey or…