After releasing the first beta of iOS 9.2.1 to developers earlier today, Apple also seeded OS X El Capitan 10.11.3 beta 1 to members of the Apple Developer Program.
The first beta of what would become El Capitan’s third major software update since its October 2015 debut carries a build number of 15D9c and is available as a standalone download through Apple’s portal for developers or through the Mac App Store’s Update tab on Macs enrolled in the beta program.
Release notes accompanying the download say that this pre-release edition of the OS X El Capitan 10.11.3 software update will improve the stability, compatibility and security of your Mac, but make no mention of potential new features or enhancements.
We’ll be updating the post with changes as we encounter them. As a refresher, OS X El Capitan 10.11.2 Â was released for public consumption less than two weeks ago.