Apple today seeded the second beta of an upcoming macOS Mojave 10.14.3 update to developers, a little over a week after releasing the first beta and two weeks since the launch of macOS Mojave 10.14.2.
The new macOS High Sierra 10.14.3 beta can be downloaded through the Software Update mechanism in System Preferences after the proper profile has been installed from Apple's Developer Center.
We don't yet know what improvements the third update to macOS Mojave will bring, but it is likely to include bug fixes and performance improvements for issues that weren't able to be addressed in the macOS 10.14.2 update.
No new features were found in the first beta of macOS 10.14.3, but if we find anything new in the second beta, we'll update this post.
Update: Apple has made a new beta of macOS Mojave 10.14.3 available to public beta testers.