/AI6h ago

Anthropic launches Claude Fable 5, its first Mythos-class model, claiming it outperforms all its previous systems

The model targets coding, computer vision, and scientific research

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Markus Anderljung@Manderljung#1981inAI

Anthropic's Fable 5 is out – the first Mythos-class model the public can use. A few things I found notable in the blog post, beyond it seeming like a very impressive model (I'm excited to try it out!):

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.

10:56 AM · Jun 9, 2026 · 2K Views
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Markus Anderljung@Manderljung

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.

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Markus Anderljung@Manderljung

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).

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Markus Anderljung@Manderljung

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?

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Markus Anderljung@Manderljung

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.

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