Mythos 5.1

Anthropic launched Claude Fable 5.1 and Claude Mythos 5.1, claiming the top spot on Artificial Analysis's Intelligence Index at 66. Cache-read pricing dropped 75% to $0.25 per million tokens, but a 1.7x increase in output token usage pushes net per-task cost up 20%.

Anthropic has released Claude Fable 5.1, an upgrade to its top-tier Fable 5 model launched in June, alongside a restricted-access sibling called Mythos 5.1. The company claims the new model matches or beats Fable 5's performance while cutting costs by up to 45% on agentic workloads through reduced cache-read pricing.