Preview at WWDC likely in June, followed by September launch.
Apple Seeds Fifth OS X 10.11.2 El Capitan Beta to Developers and Public Beta Testers
The fifth beta, build 15C48a, is available through the Software Update mechanism in the Mac App Store and can be downloaded through the Apple Developer Center. Public beta testers can download the beta through the Mac App Store.
OS X 10.11.2 appears to be an under-the-hood update as the four previous betas have not included any apparent outward-facing changes. OS X 10.11.2 is likely to include bug fixes, security enhancements, and performance improvements to address problems that have popped up since the release of OS X 10.11.1.
Apple's release notes for OS X 10.11.2 have asked developers to focus on Networking, Graphics, Mail, Wi-Fi, Calendar, USB, Notes, Photos, and Spotlight.