Introducing Claude Fable 5.1

Claude Fable 5.1 is the latest upgrade to our most capable class of models. It excels at complex, long-running tasks, and its research capabilities offer an early glimpse of how AI will contribute to scientific progress. It excels at complex, multi-step work, like a long mathematical proof or a contract with hundreds of cross-references. It avoids shortcuts and is smart enough to fix the root causes of software issues. Across our benchmarks, Fable 5.1 sets a new standard, and at lower effort levels it can achieve similar or better results than Fable 5 at a much lower cost. Claude Fable 5.1 is available everywhere today. Read more: https://www.anthropic.com/claude-fable-and-mythos-5-1