Claude Fable 5 Release Deep-Dive — Features, Benchmarks, Pricing, the Mythos Difference, and a New Safety Design
On June 9, 2026, Anthropic released Claude Fable 5 — unleashing, for the first time in a form ordinary users and developers can use, capability at the level of "Mythos," the frontier model long considered its most powerful internally. Anthropic positions it as the most powerful model it offers generally, with the tagline "built for long-running, complex work." This deep-dive, written so beginners can follow, covers what Fable 5 is (a public, safe form of Mythos-class capability, optimized for finishing a marathon rather than a single Q&A; model ID claude-fable-5), how it differs from its twin Mythos 5 (identical inside, only the safeguards differ; the public uses Fable), the benchmarks (SWE-Bench Pro 80.3% vs Opus 4.8 69.2 and GPT-5.5 58.6, a first-ever 90%+ on Hex long-running analysis, top on Cognition FrontierCode and Hebbia finance, new SOTA in vision playing Pokémon unaided), its real strength in long-running autonomy (focus across millions of tokens, 12-hour runs, Stripe completing a 50-million-line Ruby migration in one day versus two-plus months by hand, file memory boosting a game task 3x more than Opus 4.8, GitHub reporting high-autonomy long-horizon coding), pricing and availability ($10 input / $50 output per 1M tokens, 1M context and 128K output, free within each plan June 9-22 then credits, API claude-fable-5 and GitHub Copilot), a direct comparison with Opus 4.8 (standard $5/$25 vs $10/$50, +11.1 points on SWE-Bench Pro, same 1M context, Opus 4.8 Fast Mode at $10/$50; split heavy work to Fable 5 and the everyday to Opus 4.8 standard), the highlight new safety design (cyber, bio-chemistry, and distillation classifiers that fall back to Opus 4.8 only when dangerous, triggering in under 5% of sessions so 95%+ run at full performance, with 30-day retention of Mythos-class traffic), the context of releasing days after warning AI is too dangerous (a third path that closes only the dangerous areas), and when to use it. Figures are quoted from Anthropics announcement and reports and may change.