Preview at WWDC likely in June, followed by September launch.
Apple Seeds Fifth OS X El Capitan Beta to Developers
Today's update is available through the software update mechanism in the Mac App Store and through the Apple Developer Center.
It is not clear if this update will add any outward-facing changes to El Capitan, as the past few betas have focused on under-the-hood performance improvements and bug fixes to optimize the operating system ahead of its public release. We'll add new features and bug fixes in beta 5 to this post should any tweaks be discovered.
As an update complementary to OS X Yosemite, OS X El Capitan builds on the myriad features introduced last year. Behind-the-scenes improvements in El Capitan make a number of apps and processes on the Mac faster, and the introduction of Metal makes system-level graphics rendering 40 percent more efficient.
El Capitan introduces a new system-wide font, a revamped Mission Control feature, a split-view feature for using two full-screen apps at once, deeper functionality for Spotlight, and improvements to Safari that include Pinned Sites and a universal mute button.
OS X 10.11 El Capitan is currently available to both registered developers and public beta testers. Apple plans to release El Capitan to the public in the fall.