Apple today seeded the fourth beta of an upcoming macOS High Sierra 10.13.3 update to developers, one week after seeding the third beta and more than a month after releasing macOS High Sierra 10.13.2, the second major update to the macOS High Sierra operating system.
The new macOS High Sierra 10.13.3 beta can be downloaded from the Apple Developer Center or through the Software Update mechanism in the Mac App Store with the proper profile installed.
It's not yet clear what improvements the third update to macOS High Sierra will bring, but it's likely to include bug fixes and performance improvements for issues that weren't addressed in macOS High Sierra 10.13.2.
The previous macOS High Sierra 10.13.2 update focused solely on security fixes and performance improvements, with no new features introduced.
Update: Apple has also seeded a new public beta of macOS High Sierra 10.13.3 to public beta testers.