We have been observing the next generation of the Audi A4 on the streets since December 2021, but its wagon-shaped S4 counterpart has only hit the road now.
Quad tailpipes are a sure sign that it is a premium spec: the standard A4 Avant spotted back in May only had two tailpipes.
Other than that, the prototype looks like it still has some improvement to go through before production: note the obviously placeholder taillights, for example. The interior photo is particularly interesting with a new dashboard, wheel and drive mode selector.
As for the engine bay contents, your guess is as good as ours. The big question is whether the new S4 will keep its V6 or become a hybrid. Audi plans to discontinue ICE cars completely by 2025, so this is uncertain at best.