Claude is very "American", just try asking it to use English English spelling instead of American English spelling; it lasts about 3~6 sentences before it goes back. Also there is only American English in the UI (like the spell checker, et al), in Spanish you get a choice of dialects, but not English.

In contrast, o3 seems to be considerably more British - and it doesn't suck up as much in its responses. I thought these were just independent properties of the model, but now that you mention it, could the disinclination to fawn so much be related to its less American style?