What is Claude Fable 5?

The "safeguarded twin"

Fable 5 and Mythos 5 are the same model. The difference is that Fable 5 runs a layer of safety classifiers. When a request trips a classifier in one of the covered domains — cybersecurity, biology/chemistry, or distillation — Fable 5 reroutes that specific request to Claude Opus 4.8 instead of answering with the full Mythos-class model. Anthropic reports this affects fewer than 5% of sessions, and the user is notified when a reroute happens.

Where the name comes from

Fable traces to the Latin fabula — "that which is told" — a cousin of the Greek mythos. The naming nods at the Mythos lineage while signalling the safer, public-facing edition.

Specs at a glance

• Context: 1M tokens; output: up to 128k tokens.
• Price: $10 / $50 per million tokens (input / output) after the intro window.
• Covered Model, 30-day retention, no zero-data-retention (ZDR).

Full detail on Fable 5 pricing and Mythos 5 context window.

Where you could use it

At GA, Fable 5 was offered on the Claude API, the Claude Platform on AWS, Amazon Bedrock, Google Cloud and Microsoft Foundry, and was free for Pro/Max/Team/Enterprise from June 9–22 (usage-based after June 23). That access is paused while the export-control suspension is active — see Is Fable 5 available?.