Preview at WWDC likely in June, followed by September launch.
Apple Seeds Second OS X 10.11 El Capitan Beta to Developers
The update, build 15A204h, is available through the software update mechanism in the Mac App Store and through the Apple Developer Center. Apple has also released OS X Server 5.0 beta 2.
OS X El Capitan largely builds on the features introduced with OS X Yosemite, focusing on improving performance and user experience. Behind-the-scenes improvements in El Capitan have made a number of apps and processes on the Mac much faster, and the introduction of Metal makes system-level graphics rendering 40 percent more efficient.
Along with a new systemwide font, El Capitan includes a revamped Mission Control feature, a new Split View feature for using two full-screen apps at once, deeper functionality for Spotlight, and several new features for Safari, including Pinned Sites for housing frequently-visited websites and a universal mute button that quiets all tabs.
Mail's been updated with new iOS-style gestures and Smart Suggestions, and Photos, Notes, and Maps have also gained small improvements.
OS X 10.11 El Capitan is currently only available to registered developers, but Apple plans to offer a public beta of the software in July. Following testing, El Capitan will see a final release in the fall of 2015.