What is…
API
The programmatic way to use a model from your own code or app, usually paid per token.
Chat apps are for people; APIs are for software. Through an API, developers send prompts and receive responses in code, choose the exact model, set temperature, enforce structured output and pay per million tokens used.
Every AI-powered app you use that isn't made by a lab is almost certainly calling one of these APIs under the hood.
🧠 Test yourself
Which of these describes API?
Related terms
Token
The chunk of text a model actually reads and writes — roughly ¾ of a word on average.
Structured output
Getting answers in a strict, machine-readable format like JSON or a fixed table.
Tool use (function calling)
A model's ability to call external tools — search, calculators, code, APIs — and use the results.
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