Yeah I’m fairly sure they just rebuilt the whole thing, but also the AI portion of it is all done through its partnership with Google.
So Apple mostly was focusing on keeping the indexing locally on the phone and trying to not get it sent back to Google, but who knows if it’ll work.
Obviously all AI requests still going to Google, but in supposedly the scanning of your local documents/data isn’t.
(This was discussed in the Devlopers keynote, where they openly stated “you know how you would search for things in mail or elsewhere and it just wouldn’t show up when you knew it’s there, us too…” Paraphrasing but yeah, they started over with how it indexes ALL of your data apparently)