Anthropic launches Claude Fable 5 and Mythos 5
Anthropic launched two frontier models on June 9: Fable 5, the public version with a reinforced safety layer, and Mythos 5, which shares the same underlying weights.
The launch
On June 9, 2026, Anthropic launched two models: Claude Fable 5, the public version with a reinforced safety layer, and Claude Mythos 5, which shares the same weights and training as Fable 5, differing only in the safety layer wrapped around it.
Availability
Fable 5 became available in GitHub Copilot for Pro+, Max, Business and Enterprise subscribers on the same day, June 9, reinforcing Anthropic's strategy of distributing its models through developer-tool partners in addition to direct access.
What happened next
Three days after launch, the US government ordered the suspension of access to both models over national security concerns — an episode covered in another article in this edition.
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