Mythos? No, meet the new Claude Fable
Considered as a Mythos-class model, Anthropic’s new release is now available to the public.
According to an official video and materials released by Claude, Mythos is a model class that is too strong and intelligent to be widely used by the public, primarily due to its capabilities related to identifying vulnerabilities and other high-risk domains.
Claude Fable 5
Therefore, efforts were directed toward Claude Fable 5. The goal was to deliver Mythos-level capability, but with strong enough safeguards so that the model wouldn’t pose a danger in sensitive areas currently present on the internet.
The safeguards were specifically aimed at cybersecurity and biology content. Interestingly, these topics will not simply be ignored, but rather passed on to Opus 4.8 when necessary.
According to Anthropic, these safeguards are triggered erroneously in less than 5% of sessions.
In the text released on their website, it is quite explicit that more models will be released in the coming months, which is amusing considering that Anthropic itself recently proposed a global pause on the development of increasingly powerful AI systems.
“We believe it would be good for the world to have the option to temporarily slow down or pause AI development, to allow social structures and alignment research to keep pace with the advance of the technology,” stated Anthropic.
Pricing and availability
Fable 5 is priced at $10 per million input tokens and $50 per million output tokens.
This value is lower than the Claude Mythos Preview and, at the same time, positions the model as a highly advanced public option within Anthropic’s lineup.
The marketing this time around is not just about the model’s intelligence, but also the amount of time it can spend on a given task, which they claim can span days.
“The more time it spends on a task, the wider the gap between Fable and other models.”
Practical cases
In testing, Stripe stated that Fable 5 was able to mitigate months of work in just a few days.
Within a system with 50 million lines of Ruby code, the model executed a complete structural migration in 24 hours, a task that would have required more than two months of work.
Vision and prolonged execution
Anthropic promises that Fable 5 provides a new baseline for activities involving visual processing.
It even managed to beat Pokémon FireRed using only a minimal, exclusively vision-based interface, without tools and without a proper harness.
