Fable 5.1 and Mythos 5.1 are here
Anthropic: Introducing Claude Fable 5.1 and Claude Mythos 5.1
Claude Fable 5.1 and Claude Mythos 5.1 are the same model, but with different levels of safeguards.
I think a lot of us believed Fable 5 was the same as Mythos, just with different safeguards, but I don't believe Anthropic ever officially confirmed that. It's good to have the confirmation in this model update.