Anthropic has introduced Claude Fable 5.1 and Claude Mythos 5.1, described as the world's most advanced models for coding and knowledge work. Fable 5.1 is generally available, while Mythos 5.1 targets trusted access programs with enhanced safeguards for cybersecurity and life sciences. A key update is pricing, with Fable 5.1 costing an estimated 25% less than its predecessor, driven by reduced cache read costs.

For highly agentic workloads, savings can reach up to 45%. In terms of data privacy, Anthropic unveiled Enterprise Frontier Safeguards (EFS), allowing customers to store data in their own cloud infrastructure, effectively providing zero data retention while maintaining state-of-the-art adversarial prevention. Until EFS launches later this fall, eligible customers can use Fable 5.1 with zero data retention.

Regarding safety, the new safeguards have reduced false positives by 60% in cybersecurity, allowing the model to discover software vulnerabilities without generating exploits. In biology, an access program partnered with the US government will enable Mythos 5.1's advanced capabilities. Performance benchmarks indicate Fable 5.1 sets a new standard for coding and long-running problem-solving tasks, achieving results similar to Fable 5 but at lower cost and default effort levels.