After releasing beta 2 a couple of weeks ago, Apple today released the third build of macOS High Sierra 10.13.4 for testing on the Mac before a public release in the future. To install the build, head over to the “Updates” tab in the App Store and check for updates. There, you’ll find the new build ready to install. Just click the “Update” button next to the macOS High Sierra 10.13.4 beta listing and restart your Mac. The process may take a little while, so be patient and don’t turn off your Mac manually if you don’t have to.
So far, there hasn’t been any noticeable changes spotted in the new beta but we’ll let you know if we find anything down the line. As for now, it looks like only bug fixes and system stabilities are present. Messages in iCloud is present, however.