No, I have not got the wrong number. Apple this afternoon launched the macOS Big Sur 11.4 first beta, even though version 11.3 is still in the preliminary phase (the Release Candidate version was released yesterday, after the event). If you are part of the Apple Developer Program, you can download this beta as if it were another stable update.
Bearing in mind that we are going to see important news in macOS Big Sur 11.3, version 11.4 it will perhaps be a version with less details. Anyway, you have to wait for the experts to search the source code of the new beta in search of surprises, which can always exist.
Latest development builds before WWDC21
macOS 11.4 it may be the latest relevant macOS Big Sur update before seeing macOS 12, the successor to Big Sur, unveiled at WWDC21. We do not know if it will be related to more hardware news, although there are no rumors to corroborate it. Maybe we have minor news in some service.
If you are not a programmer we do not recommend that you install this beta: it is an unstable version and intended to be tested by an expert. The best thing to do is wait to download the final and stable version of macOS Big Sur 11.4 as soon as it is available.