There's not really a standard definition of an AI PC, but if there's anything beyond marketing, it would take the form of a neural processing unit, which supposedly makes some AI-related task fast by providing hardware acceleration. Cited examples include voice recognition and "training models", although I'm pretty sceptical about the later being at any significant scale.

I suspect what it will actually boil down to in many cases is having recall enabled by default and an always-listening voice assistant.