User Guide
Keys, authentication, limits, errors, and billing
Once the Quick Start is working, these pages cover how the API behaves day to day: how keys work, which models you can call, what happens when you hit a limit, and how usage is billed.
Keys & authentication
Create and revoke keys, send Authorization, and read 401 / 403.
Models & parameters
List models, pick an id, and the Chat Completions fields you will use most.
Rate limits & errors
Rate-limit headers, backoff for 429, and the rest of the error table.
Usage & billing
The usage object, streaming token counts, and where to see remaining balance.