Game company Microsoft shared that video games installed on the Xbox Series S will not have the same size when installed on the Xbox Series X.
Director of Program Management Jason Ronald recently explained to IGN about the difference in game sizes on both next-gen console systems. Since the Xbox Series S is not 4K native and will only be on 1440p, the assets installed in the hard drives will be smaller. The Xbox Series X is the opposite since it has capabilities that go up to 8K resolution, so the assets needed to be installed will be larger.
Ronald explains further:
With a performance target of 1440p at 60 fps, our expectation is that developers will not ship their highest level mipmaps to Xbox Series S, which will reduce the size of the games. Ultimately the controls in the developer’s hands. We’ve had this technology for a while that allows developers to intelligently choose which assets to install on which device they’re playing on. So the flexibility is in the developers’ hands to make sure the right assets are there.
This correlates to a news article reported here at Sirus Gaming where the Xbox Series S will not have Xbox One X enhancement when it comes to backwards compatibility. Since it can only display native 1440p resolutions, it does not have the capability to enhance it further.