---
title: Responses API
description: Use Responses-compatible structured input, instructions, and model-supported reasoning or tools.
lastUpdated: 2026-09-08
---

Send a JSON request to `POST /v1/responses` with `Authorization: Bearer YOUR_API_KEY`.

## Parameters

| Parameter | Required | Meaning |
| --- | --- | --- |
| `model` | Yes | Exact currently available model ID. |
| `input` | No | Text or supported multimodal input. |
| `instructions` | No | System-level instructions controlling the model's role or behavior. |
| `previous_response_id` | No | Previous response ID, only where the selected model and route support continuation. Context billing also depends on that route. |
| `truncation` | No | Truncation policy: `auto` or `disabled`, where supported. |

Responses compatibility does not guarantee that every model supports every tool, reasoning setting, or continuation feature. Check [Model Square](https://infistar.ai/pricing), then test the exact capability your application needs.

For the Codex client, see [Codex setup](/en/client-integrations/codex). For message-based clients, see [Chat Completions](/en/api-reference/chat-completions).