Yes and 4k will mean not-always-4k.
Codemasters have already confirmed they will be employing dynamic resolution in DIRT 5 and that the game, whilst unfinished, isn't a locked 60 in some modes - they also mentioned how they'd be dialling back crowds, cloud quality, shadowing and so on for Series S in the same way they would do for base models vs. pro models which was another confirmation that Series S is not just Series X at a lower resolution.