ArticlePublished June 10, 2026
Claude Fable 5: Anthropic Just Shipped Its Most Powerful Model Yet — and Split It in Two
On June 9, 2026, Anthropic released Claude Fable 5, the most powerful AI model it has ever made broadly available — and did something unprecedented: it shipped one frontier model as two products. Fable 5 introduces the new "Mythos" tier above Opus, leading benchmarks like SWE-Bench Pro (80.3%) and excelling at long-horizon coding, vision, and research. Its locked-down twin, Mythos 5, is the same model with safeguards lifted, restricted to vetted partners. With a 1M-token context window, always-on reasoning, and smart Opus 4.8 fallbacks, Fable 5 is built for complex, autonomous work. Here's what changed and what it means for builders.