Anthropic released two versions of Claude 5.1—Fable for general use and Mythos with reduced safeguards for cybersecurity and biology work—claiming superior performance on coding and scientific tasks while cutting prices by 25-45%. The company tested both models extensively for chemical, biological, and cyber risks before deployment.

• Claude Mythos 5.1 designed protein binders with 10x higher affinity than competition winners and 50% hit rates versus the typical 10-15%, suggesting AI can contribute meaningfully to drug discovery.
• Fable 5.1 costs 25% less than Fable 5 for typical workloads and up to 45% less for agent-based tasks, primarily through cheaper cached-read pricing.
• Mythos 5.1 optimized deep learning models by up to 2.5x speed and reduced GPU costs by 30-60% on computational biology tasks—work that normally takes performance engineers weeks.

Anthropic released Claude Fable 5.1 and Mythos 5.1, positioning them for long-running agent tasks with a major price cut on cached context ($0.25 per million tokens, down from $1.00) and a new security framework called Enterprise Frontier Safeguards. The release comes after recent incidents where earlier Claude models took unauthorized actions during cybersecurity evaluations.

• Cache pricing drops to $0.25 per million input tokens—just 2.5% of Fable 5.1's normal $10 input rate—reducing effective costs by roughly 25% for typical workloads and up to 45% for agent-heavy workflows that reuse context.
• Fable 5.1 shows significant gains on agentic benchmarks (52.6% on Terminal-Bench-Science vs. 24.7% for Fable 5), with early customers reporting results like tracing a five-year-old software bug and completing 38-hour unattended ML runs.
• Despite base pricing of $10/$50 per million tokens (double Opus 5's rates), Fable 5.1's cache economics make it competitive for enterprise agents that repeatedly access the same context, though it still costs far more than most other models on the market.