Cognition & learningGlobal+4 clusters01
Claude Opus 5 is more capable—and slightly more prone to factual hallucinations
Anthropic’s system card reports broad gains for Claude Opus 5 in agentic coding, computer use, long-horizon knowledge work, and scientific reasoning. It also documents a reliability tension: on one closed-book factuality benchmark, accuracy was 11% higher than Opus 4.8 while the hallucination rate was 6% higher. Anthropic found cases where the model confidently answered despite internal uncertainty, even as its automated alignment scores and prompt-injection robustness improved.