Apple today released, for developers, the fourth beta versions of iOS 11.4 (compilation 15F5071a), from macOS High Sierra 10.13.5 (17F66a), from watchOS 4.3.1 (15T5565a) and the tvOS 11.4 (15L5570a).
They arrive a little less than a week after the third betas and should not bring big news beyond what we already know: Messages in iCloud are again being tested on iOS and macOS, like the AirPlay 2 protocol. It is worth noting that iOS 11.4 beta 3 implied that HomePod now also has support for the Calendar app (Calendar). At watchOS, we have a new incompatibility alert for old apps and a long possibility for third-party displays on Apple Watch.
Soon, these new test compilations should also paint for members of the Apple Beta Software Program with the exception of watchOS, of course, which does not participate in it.