With CBR draw calls don't draw to
the full frame buffer (which would be native) but to a checkerboard pattern with less the pixels (hence the name), the rest of the pixels is extrapolated with data from the last frame (most common used implementation of CBR is a 50/50 split of pixels but you can go with any split you chose to), Temporal injection instead uses data from previous frames of a lower native resolution to extrapolate the 4K image.
Not exact matches
However, during the GDC 2018 Optimizing UE4 for Fortnite: Battle Royale presentation, Epic showed a slide indicated that they are targeting a
full 4K (2160p) resolution as the max
frame buffer soon on the console.
Whether a game streams at 30 or 60
frames per second, you'll be able to play it in
full 1080p with very little
buffering and only a few moments of lag or stuttering.