The Series S runs the quality mode 55% lower than the other two consoles at 2560x1440 — if this is a dynamic solution, which there is always a chance that it is, then I never spotted any points where it dropped below.
The Series S still tops out at 1440p… so long as you look at the sky, because in action it is often 2080x1170 or a straight 1080p resolution, and can even go as low as 1792x1008 in a good selection of areas.