API ReferenceResponses API Alpha

Basic Usage

Getting started with the Responses API Alpha
Alpha API

This API is in alpha stage and may have breaking changes.

The Responses API Alpha supports both simple string input and structured message arrays, making it easy to get started with basic text generation.

Simple String Input

The simplest way to use the API is with a string input:

1const response = await fetch('https://openrouter.ai/api/alpha/responses', {
2  method: 'POST',
3  headers: {
4    'Authorization': 'Bearer YOUR_OPENROUTER_API_KEY',
5    'Content-Type': 'application/json',
6  },
7  body: JSON.stringify({
8    model: 'openai/o4-mini',
9    input: 'What is the meaning of life?',
10    max_output_tokens: 9000,
11  }),
12});
13
14const result = await response.json();
15console.log(result);

Structured Message Input

For more complex conversations, use the message array format:

1const response = await fetch('https://openrouter.ai/api/alpha/responses', {
2  method: 'POST',
3  headers: {
4    'Authorization': 'Bearer YOUR_OPENROUTER_API_KEY',
5    'Content-Type': 'application/json',
6  },
7  body: JSON.stringify({
8    model: 'openai/o4-mini',
9    input: [
10      {
11        type: 'message',
12        role: 'user',
13        content: [
14          {
15            type: 'input_text',
16            text: 'Tell me a joke about programming',
17          },
18        ],
19      },
20    ],
21    max_output_tokens: 9000,
22  }),
23});
24
25const result = await response.json();

Response Format

The API returns a structured response with the generated content:

1{
2  "id": "resp_1234567890",
3  "object": "response",
4  "created_at": 1234567890,
5  "model": "openai/o4-mini",
6  "output": [
7    {
8      "type": "message",
9      "id": "msg_abc123",
10      "status": "completed",
11      "role": "assistant",
12      "content": [
13        {
14          "type": "output_text",
15          "text": "The meaning of life is a philosophical question that has been pondered for centuries...",
16          "annotations": []
17        }
18      ]
19    }
20  ],
21  "usage": {
22    "input_tokens": 12,
23    "output_tokens": 45,
24    "total_tokens": 57
25  },
26  "status": "completed"
27}

Streaming Responses

Enable streaming for real-time response generation:

1const response = await fetch('https://openrouter.ai/api/alpha/responses', {
2  method: 'POST',
3  headers: {
4    'Authorization': 'Bearer YOUR_OPENROUTER_API_KEY',
5    'Content-Type': 'application/json',
6  },
7  body: JSON.stringify({
8    model: 'openai/o4-mini',
9    input: 'Write a short story about AI',
10    stream: true,
11    max_output_tokens: 9000,
12  }),
13});
14
15const reader = response.body?.getReader();
16const decoder = new TextDecoder();
17
18while (true) {
19  const { done, value } = await reader.read();
20  if (done) break;
21
22  const chunk = decoder.decode(value);
23  const lines = chunk.split('\n');
24
25  for (const line of lines) {
26    if (line.startsWith('data: ')) {
27      const data = line.slice(6);
28      if (data === '[DONE]') return;
29
30      try {
31        const parsed = JSON.parse(data);
32        console.log(parsed);
33      } catch (e) {
34        // Skip invalid JSON
35      }
36    }
37  }
38}

Example Streaming Output

The streaming response returns Server-Sent Events (SSE) chunks:

data: {"type":"response.created","response":{"id":"resp_1234567890","object":"response","status":"in_progress"}}
data: {"type":"response.output_item.added","response_id":"resp_1234567890","output_index":0,"item":{"type":"message","id":"msg_abc123","role":"assistant","status":"in_progress","content":[]}}
data: {"type":"response.content_part.added","response_id":"resp_1234567890","output_index":0,"content_index":0,"part":{"type":"output_text","text":""}}
data: {"type":"response.content_part.delta","response_id":"resp_1234567890","output_index":0,"content_index":0,"delta":"Once"}
data: {"type":"response.content_part.delta","response_id":"resp_1234567890","output_index":0,"content_index":0,"delta":" upon"}
data: {"type":"response.content_part.delta","response_id":"resp_1234567890","output_index":0,"content_index":0,"delta":" a"}
data: {"type":"response.content_part.delta","response_id":"resp_1234567890","output_index":0,"content_index":0,"delta":" time"}
data: {"type":"response.output_item.done","response_id":"resp_1234567890","output_index":0,"item":{"type":"message","id":"msg_abc123","role":"assistant","status":"completed","content":[{"type":"output_text","text":"Once upon a time, in a world where artificial intelligence had become as common as smartphones..."}]}}
data: {"type":"response.done","response":{"id":"resp_1234567890","object":"response","status":"completed","usage":{"input_tokens":12,"output_tokens":45,"total_tokens":57}}}
data: [DONE]

Common Parameters

ParameterTypeDescription
modelstringRequired. Model to use (e.g., openai/o4-mini)
inputstring or arrayRequired. Text or message array
streambooleanEnable streaming responses (default: false)
max_output_tokensintegerMaximum tokens to generate
temperaturenumberSampling temperature (0-2)
top_pnumberNucleus sampling parameter (0-1)

Error Handling

Handle common errors gracefully:

1try {
2  const response = await fetch('https://openrouter.ai/api/alpha/responses', {
3    method: 'POST',
4    headers: {
5      'Authorization': 'Bearer YOUR_OPENROUTER_API_KEY',
6      'Content-Type': 'application/json',
7    },
8    body: JSON.stringify({
9      model: 'openai/o4-mini',
10      input: 'Hello, world!',
11    }),
12  });
13
14  if (!response.ok) {
15    const error = await response.json();
16    console.error('API Error:', error.error.message);
17    return;
18  }
19
20  const result = await response.json();
21  console.log(result);
22} catch (error) {
23  console.error('Network Error:', error);
24}

Multiple Turn Conversations

Since the Responses API Alpha is stateless, you must include the full conversation history in each request to maintain context:

1// First request
2const firstResponse = await fetch('https://openrouter.ai/api/alpha/responses', {
3  method: 'POST',
4  headers: {
5    'Authorization': 'Bearer YOUR_OPENROUTER_API_KEY',
6    'Content-Type': 'application/json',
7  },
8  body: JSON.stringify({
9    model: 'openai/o4-mini',
10    input: [
11      {
12        type: 'message',
13        role: 'user',
14        content: [
15          {
16            type: 'input_text',
17            text: 'What is the capital of France?',
18          },
19        ],
20      },
21    ],
22    max_output_tokens: 9000,
23  }),
24});
25
26const firstResult = await firstResponse.json();
27
28// Second request - include previous conversation
29const secondResponse = await fetch('https://openrouter.ai/api/alpha/responses', {
30  method: 'POST',
31  headers: {
32    'Authorization': 'Bearer YOUR_OPENROUTER_API_KEY',
33    'Content-Type': 'application/json',
34  },
35  body: JSON.stringify({
36    model: 'openai/o4-mini',
37    input: [
38      {
39        type: 'message',
40        role: 'user',
41        content: [
42          {
43            type: 'input_text',
44            text: 'What is the capital of France?',
45          },
46        ],
47      },
48      {
49        type: 'message',
50        role: 'assistant',
51        id: 'msg_abc123',
52        status: 'completed',
53        content: [
54          {
55            type: 'output_text',
56            text: 'The capital of France is Paris.',
57            annotations: []
58          }
59        ]
60      },
61      {
62        type: 'message',
63        role: 'user',
64        content: [
65          {
66            type: 'input_text',
67            text: 'What is the population of that city?',
68          },
69        ],
70      },
71    ],
72    max_output_tokens: 9000,
73  }),
74});
75
76const secondResult = await secondResponse.json();
Required Fields

The id and status fields are required for any assistant role messages included in the conversation history.

Conversation History

Always include the complete conversation history in each request. The API does not store previous messages, so context must be maintained client-side.

Next Steps