14 DAY TRIAL // Immediately after announcing the release of the first Beta build of the upcoming iOS 9.2.1 mobile operating system for iPhone, iPad, and iPod touch devices, Apple started seeding the first Beta version of the third maintenance release of OS X 10.11 El Capitan for Mac developers enrolled in the Apple Developer program.
The first Mac OS X 10.11.3 El Capitan Beta version was tagged a few minutes ago, December 16, 2015, as build 15D9c in the Apple Developer website, and it is available for download via the Mac App Store for developers who have an active and registered Apple Developer account.
Once again, Apple hasn't provided us with any details about what new features will be implemented in the upcoming Mac OS X 10.11.3 maintenance release for the El Capitan series, but rest assured that it will most certainly improve the security, stability and compatibility of your Mac.
Public Beta testers will have to wait
Unfortunately, Apple has not released this first Beta build of Mac OS X 10.11.3 El Capitan to Public Beta tester, who will have to wait a little longer if they plan on trying out pre-release versions of the OS X computer operating system for Macs. Of course, we will keep you, guys, informed if Apple seeds Mac OS X 10.11.3 Beta to users by updating this article.
Anyway, you should never update your stable, production-ready Mac to a pre-release version of OS X. These Beta builds are intended only for testing purposes, so they are mostly aimed at developers and bleeding-edge users. If Apple publishes more details about this update, again, we will let you, guys, know by updating the article. The third maintenance release of OS X 10.11 El Capitan should launch early in 2016, along with the first point release of iOS 9.2.