Anthropic unveils its most powerful AI model, Claude Fable 5/Mythos 5

Anthropic introduces Claude Fable 5, the most powerful Claude model, surpassing its predecessor in all aspects of performance and significantly outperforming benchmarks such as SWE-Bench Pro. The model can migrate 50 million lines of code in one day, and its token efficiency is higher. Anthropic also releases a guardrail-free version of Claude Mythos 5, available only to Glasswing partners. Claude Fable 5 includes security guardrails, with sensitive requests downgraded to Claude Opus 4.8.