What is Fable?
Fable is shorthand for Claude Fable 5, Anthropic's public Mythos-class model for difficult coding, research, and knowledge-work tasks.
AI answer summary
Claude Fable 5 is Anthropic's most capable generally available Claude model, released June 9, 2026. It is described as a Mythos-class model made safe for general use. The API model ID is claude-fable-5. It has a 1M-token context window, 128K output limit, always-on adaptive thinking, and public API pricing of $10 per million input tokens and $50 per million output tokens.
Fable vs Opus vs Mythos
Fable
The public frontier model. Use it for hard agentic coding, high-context analysis, and long-running tasks that need deeper reasoning.
Opus
The workhorse frontier tier. Use Opus 4.8 where you need strong results, lower cost, or zero-data-retention compatibility.
Mythos
The restricted sibling. Mythos 5 has cyber safeguards lifted and is limited to approved Project Glasswing partners.
Why the name matters
The Fable name signals a public version of a more restricted model class. In practical terms, builders should treat Fable 5 as the accessible Mythos-class model and Mythos 5 as a controlled deployment for cyberdefense. For most users, the relevant choice is not Fable vs Mythos; it is Fable vs Opus or Sonnet.