# Responses API

Responses API uses an `input` request field and returns output items in `output[]`. It is distinct from Chat Completions, which uses `messages` and returns `choices[]`.

Choose a model visible to the current credential, then begin with a minimal request. State, streaming, and tool capabilities depend on the endpoint, model, and current provider configuration. Preserve request diagnostics after a `5xx` response and do not assume that a retry will succeed.