> ## Documentation Index
> Fetch the complete documentation index at: https://openrouter.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Responses API

> OpenAI-compatible Responses API

<Info>
  **Stateless Only**

  This API is **stateless** - each request is independent and no conversation state is persisted between requests. You must include the full conversation history in each request. Requests that set `store: true` or a non-null `previous_response_id` are rejected with a `400` error.
</Info>

OpenRouter's Responses API provides OpenAI-compatible access to multiple AI models through a unified interface, designed to be a drop-in replacement for OpenAI's Responses API. This stateless API offers enhanced capabilities including reasoning, tool calling, and web search integration, with each request being independent and no server-side state persisted.

## Base URL

```lines theme={null}
https://openrouter.ai/api/v1/responses
```

## Authentication

All requests require authentication using your OpenRouter API key:

<CodeGroup>
  ```typescript title="TypeScript" lines theme={null}
  const response = await fetch('https://openrouter.ai/api/v1/responses', {
    method: 'POST',
    headers: {
      'Authorization': 'Bearer YOUR_OPENROUTER_API_KEY',
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      model: 'openai/o4-mini',
      input: 'Hello, world!',
    }),
  });
  ```

  ```python title="Python" lines theme={null}
  import requests

  response = requests.post(
      'https://openrouter.ai/api/v1/responses',
      headers={
          'Authorization': 'Bearer YOUR_OPENROUTER_API_KEY',
          'Content-Type': 'application/json',
      },
      json={
          'model': 'openai/o4-mini',
          'input': 'Hello, world!',
      }
  )
  ```

  ```bash title="cURL" lines theme={null}
  curl -X POST https://openrouter.ai/api/v1/responses \
    -H "Authorization: Bearer YOUR_OPENROUTER_API_KEY" \
    -H "Content-Type: application/json" \
    -d '{
      "model": "openai/o4-mini",
      "input": "Hello, world!"
    }'
  ```
</CodeGroup>

## Core Features

### [Basic Usage](./basic-usage)

Learn the fundamentals of making requests with simple text input and handling responses.

### [Reasoning](./reasoning)

Access advanced reasoning capabilities with configurable effort levels and encrypted reasoning chains.

### [Tool Calling](./tool-calling)

Integrate function calling with support for parallel execution and complex tool interactions.

### [Web Search](./web-search)

Enable web search capabilities with real-time information retrieval and citation annotations.

## Error Handling

The API returns structured error responses:

```json lines theme={null}
{
  "error": {
    "code": "invalid_prompt",
    "message": "Missing required parameter: 'model'."
  },
  "metadata": null
}
```

For comprehensive error handling guidance, see [Error Handling](./error-handling).

## Rate Limits

Standard OpenRouter rate limits apply. See [API Limits](/docs/api_reference/limits) for details.