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Anthropic launches Fable 5.1 and Mythos 5.1
A shared-model update expands research and coding under differentiated access.
Model labAnthropic
AnthropicTopics
OCCURRED1 Sept 2026
PUBLIC ACCOUNT1 Sept 2026
EVIDENCEFirst-party account
About these dates
Date of the developer announcement or dated release record.
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 ↗
Sources & attribution
- Organizational disclosure 1 Sept 2026Anthropic launches Fable 5.1 and Mythos 5.1 ↗
Anthropic. Original developer announcement.
- Organizational disclosure Accessed 11 Sept 2026Anthropic newsroom: September 1 launch ↗
Anthropic. Developer newsroom.