o3 and o4-mini are large language models recently realeased by OpenAI and augmented with chain-of-thought reinforcement learning, designed to “think before they speak” by generating explicit, multi-step reasoning before producing an answer. How good these reasoning models are in chess? Using a simple four-move sequence, I suceed to force o3 into an illegal move, and across multiple matches both o3 and o4-mini struggle dramatically, by generating illegal moves in over 90% of cases and even...
