Claude models: Fable vs. Opus vs. Sonnet vs. Haiku

Anthropic’s Claude family has four primary models: Haiku, Sonnet, Opus, and Fable. The version numbers are inconsistent between them; as I write this, Opus 5.5 just dropped, Fable 5.1 came out on September 1, 2026, Sonnet 5 was released on June 30, 2026, and Haiku is still on 4.5 and launched in October 2025—though a new model is due out soon. There’s also Mythos, but the general public doesn’t have access to that.