What is API?

An Application Programming Interface — how developers integrate an AI model into their own apps and pay per usage (tokens).

An API (Application Programming Interface) is the way software talks to other software. In the AI world, it means you can send a request to a model provider's servers (a prompt, an image, an audio file) and get the model's output back inside your own app, script, or workflow, without using the provider's chat interface. You sign up for an API key, call an endpoint such as a chat completion or embedding endpoint, and pay per usage, usually priced per million input and output tokens. APIs expose controls the consumer apps hide: model choice, temperature, system prompts, tool calling, and streaming. The chat product and the API are often billed separately, so a ChatGPT or Claude subscription does not include API credits. For teams, the API is what turns a model into a product feature.

Example

A startup calls the OpenAI API from its support dashboard so every incoming ticket is automatically summarized and tagged, paying only for the tokens each request uses.

Why it matters

If you want AI inside your own product or automation, you are choosing an API, not an app. Compare providers on per-token price, rate limits, model quality, and features like tool calling and caching. Browse the AI tools directory or the model leaderboard to put it into practice.