I mentioned last week that rc3 was unusually small.
Well, we fixed that. The small size of rc3 was clearly just because of pull request timing patterns, and rc4 is back up to normal size and then some.
Part of it is networking - rc3 didn't have any net updates, and rc4 does. But it's not just that, I think we just happened to have several things that shifted to this past week instead of having made it into rc3.
It is worth nothing that while this rc is the largest rc4 (at least in number of commits) that we've had in a couple of years, it's not really outrageously so - it really is just larger than usual by about the same amount that rc3 was smaller than usual.
So I'm not worried, I'm just pointing out a random and somewhat unusual pattern.
Outside of the networking changes that came in this week, there's a little bit of everything - drivers being most of it as usual (sound, gpu, hid, pinctrl, usb, misc - in addition to the networking drivers, of course). But we also have the usual arch updates (x86, arm64, s390), various tooling updates (selftests and perf), documentation, and filesystems fixes (gfs2, nfs). And fall-through comment updates (although the current discussion is about hopefully fairly soon turning the comments into actual statement attributes, which is the modern non-lint way of doing it).
The rc isn't so big that you can't just scroll through the shortlog below to get a feel for the kind of details we have. Nothing looks particularly scary, although the swapgs speculation thing made the news, I guess.