Linus has tagged the 5.4-rc1 release, thus ending the merge window for this development cycle. An apparent linux-kernel outage means that there is no announcement to post yet; we'll do that as soon as it becomes available. Meanwhile, though, everything can be seen in his repository.
Update: the 5.4-rc1 announcement is now available. "I didn't really extend the merge window by a day here, but I gave myself an extra day to merge my pending queue. Thus the Monday date for the rc1 rather than the usual Sunday afternoon."