OpenAI's latest reasoning models are hallucinating more than ever
OpenAI just revealed that its newest reasoning models, o3 and o4-mini, hallucinate significantly more than their predecessors. On OpenAI's PersonQA benchmark, o3 hallucinated on 33% of questions—about double o1's rate—while o4-mini reached 48%. OpenAI admitted it doesn't fully understand why, noting that scaling reasoning models seems to generate more assertions, both true and false.