Claude Opus 5: The System Card
Zvi (Don't Worry About the Vase) 1 month ago 2 ● 17 sources
Anthropic released Claude Opus 5, a model positioned between Opus 4.8 and their larger Mythos 5, claiming comparable performance to Fable 5 at half the price and faster speed. Key concrete improvements include reducing prompt injection attack success rates from 5.5% to 2.0% on the IPI benchmark, cutting safety classifier false positives from 42% to 5% in FrontierBench, and achieving 69% multi-turn appropriate response rates for self-harm queries versus 58% for Fable. The model now permits vulnerability analysis in source code while maintaining blocks on binary analysis, and shows improved agentic safety and alignment compared to previous versions, though it lacks the full multi-step exploit capability of Mythos 5.
