News: Claude
Claude Fable 5.1 and Mythos 5.1 release on September 1, 2026
Claude Fable 5.1 release: Anthropic shipped Fable 5.1 and Mythos 5.1, one model with two safeguard levels, on Sep 1.
Anthropic Claude Opus 5.5 release on September 22, 2026: what's new
Claude Opus 5.5 release: Anthropic shipped the model on September 22, 2026, at Fable 5.1 level on most work.
Anthropic Claude Sonnet 5.5 release on September 28, 2026: what's new
Claude Sonnet 5.5 release: Anthropic shipped the first Sonnet with cyber safeguards on September 28, 2026.