The nightly composes switched over to using XZ today. I am not sure if
something else changed in rawhide last night, but the kde and desktop
spins each dropped about 130 MB which is a lot better than I expected
(which was mostly based on the effect I had seen on the games spin
in tests).
If you see any problems that look like they might be related using XZ for
the spins please file a bug against livecd-tools.