Claude Fable 5 API

Complete API reference for Claude Fable 5 LLM models powered by Anthropic.

Model Variants

This API supports three Claude Fable 5 model variants:

Quick Comparison

Claude Fable 5 Text to Text

Endpoint

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POST /api/v1/chat/completions

Request Parameters

Required

Message Support

Optional

Example Request

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const response = await fetch('https://api.flaq.ai/api/v1/chat/completions', {
  method: 'POST',
  headers: {
    'Authorization': 'Bearer YOUR_API_KEY',
    'Accept': 'text/event-stream',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    model: 'claude-fable-5-text-to-text',
    messages: [
      {
        role: 'user',
        content: 'Draft a technical decision memo for this architecture choice.'
      }
    ],
    stream: true,
    max_tokens: 2048,
    top_p: 0.9,
    top_k: 50
  })
});

Claude Fable 5 Web Search

Endpoint

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POST /api/v1/chat/completions

Request Parameters

Required

Message Support

Optional

Example Request

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const response = await fetch('https://api.flaq.ai/api/v1/chat/completions', {
  method: 'POST',
  headers: {
    'Authorization': 'Bearer YOUR_API_KEY',
    'Accept': 'text/event-stream',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    model: 'claude-fable-5-web-search',
    messages: [
      {
        role: 'user',
        content: 'Find the latest public information about Claude Fable 5 and summarize it for a product brief.'
      }
    ],
    stream: true,
    max_tokens: 2048,
    top_p: 0.9,
    top_k: 50
  })
});

Claude Fable 5 File Analysis

Endpoint

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POST /api/v1/chat/completions

Request Parameters

Required

Message Support

Optional

Example Request

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const response = await fetch('https://api.flaq.ai/api/v1/chat/completions', {
  method: 'POST',
  headers: {
    'Authorization': 'Bearer YOUR_API_KEY',
    'Accept': 'text/event-stream',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    model: 'claude-fable-5-file-analysis',
    messages: [
      {
        role: 'user',
        content: [
          { type: 'text', text: 'Summarize this file and extract the key risks.' },
          {
            type: 'file',
            file: {
              filename: 'demo.pdf',
              file_data: 'https://example.com/demo.pdf'
            }
          }
        ]
      }
    ],
    stream: true,
    max_tokens: 4096,
    top_p: 0.9,
    top_k: 50
  })
});

Response Format

Claude Fable 5 LLM models return OpenAI-compatible completion responses. With stream: true, the response is Server-Sent Events; with stream: false, the response is a single JSON object.

Successful Response

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data: {"id":"chatcmpl-...","object":"chat.completion.chunk","created":1710000000,"model":"claude-fable-5-file-analysis","choices":[{"index":0,"delta":{"role":"assistant"},"finish_reason":null}]}

data: {"id":"chatcmpl-...","object":"chat.completion.chunk","created":1710000000,"model":"claude-fable-5-file-analysis","choices":[{"index":0,"delta":{"content":"Here is a concise summary"},"finish_reason":null}]}

data: {"id":"chatcmpl-...","object":"chat.completion.chunk","created":1710000000,"model":"claude-fable-5-file-analysis","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}

data: {"id":"chatcmpl-...","object":"chat.completion.chunk","created":1710000000,"model":"claude-fable-5-file-analysis","choices":[],"usage":{"prompt_tokens":12,"completion_tokens":8,"total_tokens":20}}

data: [DONE]

Error Response

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event: error
data: {"error":{"message":"API requests too frequent, exceeding rate limit","type":"rate_limit_error","code":"1302","param":null}}

Best Practices

1. Use structured messages: Send conversation history through messages[] instead of flattening context into one prompt.
2. Choose the right model variant: Use Text to Text for text-only reasoning, Web Search when current online context is needed, and File Analysis when files or images are required.
3. Tune Claude parameters carefully: top_p and top_k are supported across Claude Fable 5 variants and can change output diversity.
4. Consume SSE events: Append choices[0].delta.content for streaming display and treat data: [DONE] as successful completion.
5. Send only supported inputs: Do not send file or image parts to Text to Text or Web Search routes.