A simple prompt that still stumps frontier LLMs most of the time is “create a pinball game”. They’ll put all the right pieces there but then fail to arrange them such that the game is truly playable. They’ll put a wall in the way of the launch chute so the ball can’t be launched. Or the flippers will pivot the wrong way. Or there will be holes such that the ball drops off the bottom without getting within reach of the flippers, etc.

Opus 5 is the first I’ve seen to “one shot” it (in a harness, so it was more than one LLM call).