[AINews] Claude Fable/Mythos 5.1: new SOTA model, 75% cache price cut but 70% more output tokens

Anthropic launched Claude Fable 5.1 and Mythos 5.1, claiming new SOTA benchmarks, with 75% cache-read price cut and 1M-token context.

Anthropic released Claude Fable 5.1 and Mythos 5.1 as flagship models for coding and knowledge work, with a 1M-token context window and pricing of $10/$50 per million input/output tokens and cache reads cut 75% to $0.25. Artificial Analysis Intelligence Index scored Fable 5.1 at 66 versus 63 for Claude Opus 5, with HLE at 59.1% and Terminal-Bench v2.1 at 91.4%, though per-task cost rose ~20% due to 1.7x output token usage. Community analysis suggested Fable and Mythos may share underlying weights with different safety/routing behavior, and release notes highlighted Enterprise Frontier Safeguards and zero-data-retention support.

• Fable 5.1 positioned for autonomous long-horizon work; Mythos 5.1 paired for knowledge work
• Benchmark gains: GDPval-AA v2 +130 Elo, AA-Briefcase +122 Elo, tau3-Banking +9 points over Fable 5
• On agentic knowledge work Fable 5.1 is roughly tied with Opus 5 on some measures
• ~4% of eval output tokens came from server-side fallback routing to Opus 4.8/Opus 5
• Launch coincides with competing releases: OpenAI Astra, Grok 4.7 and Gemini Flash 3.8 on the way