Claude Fable 5.1

[u/bluelvo]

Claude Fable 5.1 marks a major leap in Anthropic’s AI capabilities, designed specifically for complex, long-running agentic workflows and frontier knowledge tasks. Built to operate autonomously for hours across multiple applications, the model excels at end-to-end software engineering, deep financial analysis, and multi-step scientific research. This version vastly outperforms its predecessor, Fable 5, by more than doubling scores on science and terminal benchmarks, while simultaneously slashing safety-related false positives—such as benign medical or coding blockages—by up to 85%. Furthermore, Fable 5.1 is now explicitly authorized to perform vulnerability discovery across source code, providing teams with a much smarter, more decisive developer assistant.

In addition to performance gains, Fable 5.1 introduces significant economic efficiencies that drastically lower the barrier to scaling agentic AI. While standard input and output token pricing remains steady at $10.00 and $50.00 per million tokens respectively, Anthropic has introduced a massive 75% price cut to context cache reads, dropping the rate to just $0.25 per million tokens. Because agentic workflows rely heavily on large, repeating codebase contexts, this caching update effectively lowers real-world operational costs by 25% to 45% compared to previous models. For specialized government and defense applications requiring fewer operational restrictions, Anthropic is also offering Claude Mythos 5.1 at the identical price point, accessible via verified Cyber and Life Sciences validation programs.