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.

A Twitter user posted a strongly negative reaction to Claude Opus 5, expressing frustration without specifying what issues they encountered. The post is vague complaint rather than detailed technical feedback.

• A Twitter user posted a vague, negative reaction to Claude Opus 5 with no specifics or evidence.
• The post offers no benchmarks, examples, or technical details explaining what went wrong.