Anthropic just shipped the most capable model they have ever released to the public.
The clever part is not the raw power, it is how they handled the risk.
What Claude Fable 5 actually changes:
1. It is "Mythos-class", a tier that until today only ran inside Anthropic. First time this level is open to everyone.
2. Built to run for days, not minutes. It plans across stages, hands work to sub-agents, and checks its own output.
3. Stripe tested it on a 50 million line codebase and ran a migration in one day that would have taken a team two months by hand.
4. Costs $10 per million input tokens and $50 per million output. Worth it for heavy long projects, overkill for small daily tasks.
5. The safety move: dangerous queries like cybersecurity or biology do not get refused. They quietly get answered by a weaker model, Opus 4.8, instead.
Refusing every risky question looks safe but punishes real users.
Downgrading only the dangerous edge while keeping full power everywhere else is the smarter call.
Claude (@claudeai)
Introducing Claude Fable 5: a Mythos-class model that we’ve made safe for general use.
Its capabilities exceed those of any model we’ve ever made generally available.
Video
— https://nitter.net/claudeai/status/2064394146916229443#m