Do we know that? I would expect it works like Apple Watch apps do where compatible apps have an Apple Watch App extension on the phone that the thin Apple Watch App (which is basically just a SwiftUI GUI) talks to, rather than having the phone render and stream the whole screen.
edit: OK, some media outlets are saying Apple has told them "developers can bring over existing CarPlay apps", but there's no mention of it in anything Apple themselves have put out publicly which is why I was confused
edit: OK, some media outlets are saying Apple has told them "developers can bring over existing CarPlay apps", but there's no mention of it in anything Apple themselves have put out publicly which is why I was confused