Anthropic launches Fable 5.1 and Mythos 5.1

Anthropic introduced Fable 5.1 for general access and Mythos 5.1 for trusted partners on September 1, 2026, reporting improvements in research, coding and extended work. Fable gained permission for vulnerability discovery while some exploit-generation requests continued to be redirected to another model. Some biological research capabilities remained restricted to the Mythos program. Anthropic Anthropic