---
title: "Responses"
method: POST
path: "/v1/responses"
tags: ["openai-compat"]
---

# Responses

`POST /v1/responses`

## Request

- Base URL: `https://api.fastino.ai`
- URL: `https://api.fastino.ai/v1/responses`
- Auth: one of:
  - API key in header `X-API-Key`
  - HTTP bearer
- TypeScript: <https://skmtc.dev/fastino-ai/apis/pioneer-inference-api/docs/v1/responses/post.ts> (a function with typed inputs; its response is checked against the schema)

Serve an OpenAI-compatible Responses request.

## Request body

- ResponsesRequest: OpenAI-compatible Responses API request. ``input`` accepts either a plain string (convenience shorthand used by the OpenAI SDK for simple text prompts) or a list of input items.
  - `extra_body` object, nullable
  - `extra_headers` object, nullable
  - `include` string[]
  - `include_confidence` boolean, nullable
  - `include_spans` boolean, nullable
  - `input` union
    - string
    - object[]
  - `instructions` string
  - `max_output_tokens` integer, nullable
  - `metadata` object, nullable
  - `model` string, required
  - `parallel_tool_calls` boolean
  - `previous_response_id` string, nullable: Fastino inference ID or stored Responses wire ID to continue from. When present, Fastino reconstructs the prior turn from inference history and prepends it to the new input.
  - `prompt_cache_key` string, nullable
  - `reasoning` ResponsesReasoningRequest: Opt-in reasoning controls in OpenAI Responses format.
    - `effort` string, nullable: Optional reasoning effort hint, such as 'low', 'medium', or 'high'.
    - `enabled` boolean, nullable: Switch for enabling reasoning on capable models.
    - `exclude` boolean, nullable: When supported by the upstream provider, exclude reasoning text from the response while still allowing the model to use reasoning.
    - `summary` string, nullable: Optional Responses-style reasoning summary mode.
  - `service_tier` string, nullable
  - `store` boolean: Whether to store response state for turn-to-turn continuation. When true, Fastino preserves the response for previous_response_id replay, including available tool-call and reasoning context.
  - `stream` boolean
  - `task_type` string, nullable: **Deprecated.** Legacy task hint (``extract_entities`` / ``classify_text`` / ``extract_json`` / ``ner`` / ``schema``). The unified schema on ``text.format.schema`` disambiguates the task automatically. Submitting this field emits ``Deprecation: true`` and ``Sunset: <RFC 7231 date>`` headers on the response.
  - `temperature` number, nullable
  - `text` ResponsesTextRequest: Responses text controls.
    - `format` ResponsesTextFormatRequest: Structured-output controls for Responses text formatting.
      - `name` string, nullable
      - `schema` object, nullable
      - `strict` boolean, nullable
      - `type` string, nullable
    - `verbosity` string, nullable
  - `tool_choice` union
    - string
    - object
  - `tools` object[]
  - `top_p` number, nullable

## Response `200`

Successful Response

- unknown

## Other responses

- `422`: Validation Error
- `425`: The model is temporarily warming. Wait the number of seconds in `Retry-After`, then retry the same request with a bounded retry policy.

## Changes

- **2026-10-12** `43d7e06a824b`: 1 info
  - added the non-success response with the status `425`
- **2026-09-28** `54da122a2879`: 2 warning
  - removed the request property `effort`
  - removed the request property `models`
- **2026-09-23** `620970c6f5f2`: 1 info
  - endpoint added

[Operation history](https://skmtc.dev/fastino-ai/apis/pioneer-inference-api/changes/v1/responses/post.md)

---

[API](https://skmtc.dev/fastino-ai/apis/pioneer-inference-api.md) - [All operations](https://skmtc.dev/fastino-ai/apis/pioneer-inference-api/llms.txt) - [OpenAPI document](https://skmtc.dev/fastino-ai/apis/pioneer-inference-api/revisions/81465e18c1d2?raw)