Anthropic introduced Claude Fable 5.1 and Claude Mythos 5.1.

They're the world’s most advanced models for coding and knowledge work.

As well as being capable of much higher performance than Fable 5, it can also achieve similar or better results at a much lower cost when set to lower effort levels.

Cache reads with Fable 5.1 cost 75% less than Fable 5’s.

This reduces the cost of the model in practice by around 25% for typical workloads, and up to 45% for highly agentic ones.

Also introduced Enterprise Frontier Safeguards (EFS), which give enterprise customers complete privacy (the same as zero data retention), while still being state-of-the-art at preventing adversarial use. EFS rolls out in phases, starting this fall.