# System One (/docs/api/gateway/systemone)

Typed, calibrated decisions from codai-s1 in one forward pass — choice, score and yes/no questions.

`codai-s1` answers typed questions about a `state` without generating text, typically in 80–300 ms. Gate your action on the returned `confidence`, and keep your own fallback: when the model is unavailable the gateway answers `503 s1_unavailable` and never substitutes a generative model unless you ask for it.

- **Batch** — send `items: [{ id, state }]` (up to 16) instead of `state` to ask the same `questions` about several states at once; the answer is `items: [{ id, answers }]` in request order (`client.systemOne.batch(...)` / `client.system_one.batch(...)`).
- **`timeout_ms`** — 100–5000 ms budget for this call (default 1500).
- **`fallback: "codai-fast"`** — opt in to a generative fallback: when codai-s1 is unavailable, codai-fast answers the same questions with the same answer shapes, and the response carries `fallback_used: true` (plus the `x-codai-s1-fallback` header). Its probabilities are less calibrated, so lower your thresholds or log the flag.

<OpenAPIPage document="./openapi/en/gateway.yaml" operations={[{path: '/v1/systemone',method: 'post'}]} />