The model is designed to accelerate software engineering workflows.
Fable should meaningfully accelerate what you can build! Truly a step change in capabilities that delivers what we’ve come to expect from the model but weren’t quite there yet. You can move as fast you think.
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.
Users are excited about Anthropic's Claude Fable 5 model because it has accelerated their research and delivered major gains in frontier coding, drug design, and molecular biology hypothesis generation.
A new data retention policy: 30 days of all traffic on Mythos-class models, wherever they're accessed, including third parties (e.g. AWS Bedrock). Not used for training, human access logged, deleted after 30 days. Meant to thwart misuse that a classifier for a single conversation would miss.
Moving the ceiling on Frontier code, improving drug design process by 10x, coming up with novel hypothesis and research in molecular biology and genomics are some of my favorite Mythos5 capability examples.
https://www.anthropic.com/news/claude-fable-5-mythos-5
Harder to jailbreak than before: 1,000+ hours of external red-teaming turned up no universal jailbreak. Though the UK AISI "has made progress towards one" in a brief testing window. Maybe AISI will do it again?
They're setting up trusted-access programs for cyber + bio. Basically, a safeguarded model for everyone (Fable 5) – downgraded to Opus 4.8 if classifiers fire – the full-capability version for vetted users (Mythos 5).
They've also clearly put work into vision, where Claude has historically been poor. Fable 5 rebuilt a web app's source code from screenshots alone, and beat Pokémon FireRed with a minimal vision-only harness.
Our own research has moved faster these last few months than anything before it. I’ve found it most useful to implement complex infra pieces, set up experiments, debug system issues, understand all the tiny little details and surface them, and analyze my results.
The model is designed to accelerate software engineering workflows.
Fable should meaningfully accelerate what you can build! Truly a step change in capabilities that delivers what we’ve come to expect from the model but weren’t quite there yet. You can move as fast you think.
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.