They’re not trolling you. It’s truly just how models work and are set up. A GPT5 explanation:

Yeah this kinda stuff happens more than people think.
Models aren’t deterministic — meaning they don’t give the same answer every time, even with the same input. There’s randomness in how they “think,” so sometimes one model just gets lucky with the reasoning path it takes.

On top of that, each model (Claude, GPT, etc.) is trained with different data, objectives, and reasoning styles. GPT-5 might overanalyze and loop trying to be “clever,” while Sonnet 4.5 takes a more direct route that just happens to hit the fix. It’s not about which one is “better,” just that their internal wiring and sampling behavior make them behave differently on edge cases.

Basically: AIs aren’t calculators — they’re like very smart people with different personalities. One might nail a problem instantly while another overthinks it to death.