Anthropic Releases Claude Fable 5, a Guardrailed Public Version of Its Powerful Mythos AI

Anthropic is rolling out a public version of its Mythos AI model, but with guardrails barring its use in risky areas such as cybersecurity, after a preview earlier this year sent shockwaves globally with its ability to find software flaws. The new Claude Fable 5 is the most powerful model Anthropic has ever made for wider use, touting its performance in software engineering and analytics. In high-risk areas like cybersecurity, biology, chemistry, and distillation, the model blocks responses and falls back to Claude Opus 4.8. The big question is whether the guardrails are strong enough to withstand jailbreaking attempts — Anthropic says it "extensively" tested the model with hackers who tried to bypass its safeguards, and none were successful. Anthropic has so far limited Mythos access to about 200 organizations, including the U.S. government, under the Glasswing program, after announcing in April that Mythos had uncovered thousands of software vulnerabilities. Anthropic also rolled out an upgraded Mythos 5 to select customers, which "has the strongest cybersecurity capabilities of any model in the world." Offering its capabilities more widely may allow the $965 billion company to extend the momentum that has powered its valuation above rival OpenAI. Pricing on both models is $10 per million input tokens and $50 per million output tokens.