Models / Claude Fable 5

Claude Fable 5

Anthropic · claude-fable-5 Best for agents

Overview

Mythos-class reasoning for autonomous knowledge work.

Claude Fable 5 is Anthropic's Mythos-class flagship, built for long-horizon autonomous work: multi-file refactors, research synthesis and agentic pipelines that run for hours. Reasoning is always on and the effort level is tunable from low to max, so you can trade latency for depth per request. It accepts text, images and documents across a one-million-token context window.

Capabilities
Extended reasoning Tool calling Structured outputs Vision Document input Streaming Prompt caching

Call this model

curl https://open-gray.com/api/v1/chat/completions \
  -H "Authorization: Bearer sk-og-v1-..." \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-fable-5",
    "messages": [
      { "role": "user", "content": "Summarise our Q3 revenue drivers." }
    ]
  }'
Pass "stream": true for server-sent events.

Worked example

A request with a 20,000-token prompt and a 2,000-token answer on Claude Fable 5:

Input 20,000 tokens20.00 cr
Output 2,000 tokens10.00 cr
Total charged30.00 cr / $0.30