Should we not necessarily assume that it would have some FastHTML training with that March 2025 cutoff date? I'd hope so but I guess it's more likely that it still hasn't trained on FastHTML?

Claude 4 actually knows FastHTML pretty well! :D It managed to one-shot most basic tasks I sent its way, although it makes a lot of standard minor n00b mistakes that make its code a bit longer and more complex than needed.

I've nearly finished writing a short guide which, when added to a prompt, gives quite idiomatic FastHTML code.