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Claude Fable 5.1

claude-fable-5-1

Claude Fable 5.1 is a high-performance Claude model for demanding reasoning, long-horizon agentic coding, multistep research, and document, spreadsheet, and slide work. Supports text and image inputs through the OpenAI-compatible chat completions endpoint with a 1M-token context window, up to 128K output tokens, and always-on adaptive thinking controlled by effort.

Authentication

authorization string required

All APIs require authentication via Bearer Token.

Get API Key:

Visit API Key Management Page to get your API Key.

Usage:

Add to request header:

Authorization: Bearer YOUR_API_KEY

Parameters

model string required

Model ID to use for the request

Value: claude-fable-5-1

messages array required

Array of message objects representing the conversation history

role string required

Message role

Options: user, assistant, system, developer

content string | array required

Text string or multimodal array supporting text and image inputs

max_tokens integer

Maximum tokens to generate in the completion

Range: 1 - 128000

temperature number

Sampling temperature to use. Claude Fable 5.1 accepts only the default value

Default: 1.0

top_p number

Nucleus sampling parameter. Claude Fable 5.1 accepts only the default value

Default: 1.0

stream boolean

Whether to stream response incrementally

Default: false