> imagine EU iPhones being imported into US to use with OpenAI or Claude Cowork

That's not the case. it's merely software (exactly like my iPhone 16 lacking the promised AI features claimed at WWDC24).

Anyway as I'm now within the EU with phone I bought before moving to the EU, regional features (or restrictions) depends on the logged in account and device regional settings. Except physical considerations (eSIM design, actual radio transceivers). The hardware is the same thank god.