---
title: "Zero-shot text classification."
method: POST
path: "/api/ai/classify"
tags: ["ai"]
---

# Zero-shot text classification.

`POST /api/ai/classify`

## Request

- Base URL: `https://2s.io`
- URL: `https://2s.io/api/ai/classify`
- Auth: API key in header `PAYMENT-SIGNATURE`

Zero-shot text classification. POST { text, labels[], multiLabel? }. Assigns the text to one of your labels (or several when multiLabel=true) with a confidence score and a one-line rationale. No training data needed — define the labels at call time. Great for routing, tagging, triage, and intent detection. Billing: payment settles before this endpoint runs (paid upstream), so an error after settlement IS charged — the error response then carries the payment receipt (PAYMENT-RESPONSE) and `X-2s-Charged: true`.

## Query parameters

- `trial` 1

## Request body

- object
  - `text` string, required: Text.
  - `labels` string[], required: Candidate labels to choose from.
  - `multiLabel` boolean: Allow multiple labels (default single).

## Other responses

- `200` (unresolved $ref)
- `400`: Invalid request. Parameter validation (BAD_REQUEST / INVALID_PARAM with error.details.issues, MALFORMED_JSON) runs before payment and is never charged; a request-specific 400 raised by the endpoint itself runs after settlement on this paid-upstream operation and IS charged (`X-2s-Charged: true` + PAYMENT-RESPONSE receipt).
- `402`: Payment required. Body is the x402 PaymentRequirements envelope with a multi-network accepts array; the per-call price is in accepts[].amount (and on the operation as x-2s-price). Sign for whichever rail you hold USDC on (EIP-3009 for Base, partial SPL transfer for Solana) and retry with the PAYMENT-SIGNATURE header (X-PAYMENT also accepted for v1 clients). Also PAYMENT_SETTLE_FAILED (error envelope) when a verified payment failed to settle: error.details.chargeStatus is "not_charged" (retry with a fresh payment) or "unknown" (the authorization may still settle before its deadline — check it before retrying).
- `429`: Too many requests — RATE_LIMITED: our per-IP / per-payer limiter. Not charged; retry after Retry-After.
- `5XX`: Server-side failure. 500 INTERNAL: unexpected error; quote error.errorId (also the X-2s-Error-Id header). 502 UPSTREAM_UNAVAILABLE (or another UPSTREAM_* code): the data provider failed — composite endpoints refuse unbilled when every source fails. 503 SERVICE_PAUSED: endpoint paused by the operator kill switch, retry after Retry-After; 503 SPEND_CAP: daily upstream budget exhausted. 504 UPSTREAM_TIMEOUT. On a paid-upstream operation (see its description) this can follow settlement: then the call WAS charged and the response carries `X-2s-Charged: true` plus the PAYMENT-RESPONSE receipt. SERVICE_PAUSED and SPEND_CAP are never charged.

---

[API](https://skmtc.dev/2s-io/apis/2s-the-most-everything-api.md) · [All operations](https://skmtc.dev/2s-io/apis/2s-the-most-everything-api/llms.txt) · [OpenAPI document](https://skmtc.dev/2s-io/apis/2s-the-most-everything-api/revisions/da4c5caf686e?raw)