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wednesday, june 10, 2026
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Anthropic released Claude Fable 5 on June 10, 2026, a public-facing version of its Mythos-class model with strict safety guardrails that prevent it from answering certain questions like basic biology. The model ranks #1 on the Artificial Analysis Intelligence Index but faces criticism from cybersecurity researchers over overly restrictive safeguards and from users over limited free access and opaque content filtering.
- Claude Fable 5 is the public version of Mythos, a model family Anthropic previously deemed too dangerous for public release due to cybersecurity capabilities.
- Model ranks #1 on Artificial Analysis Intelligence Index but is slower and more expensive than predecessors.
- Fable 5 free access limited to June 22, 2026 across Pro, Max, Team, and Enterprise plans; permanent access requires paid subscription.
- Anthropic uses classifiers to block Fable from answering certain questions (e.g., basic biology), routing them to Claude Opus 4.8 instead.
- Cybersecurity researchers report guardrails too strict for legitimate security work; model has been jailbroken to bypass safety filters.
- System prompt leaked; users report opaque filtering and uncertainty about what the model will refuse to answer.