Preview at WWDC likely in June, followed by September launch.
Apple Releases OS X 10.11.5 El Capitan With Bug Fixes and Performance Improvements
The OS X 10.11.5 update can be downloaded through the Software Update mechanism in the Mac App Store. It is available to all OS X El Capitan users.
Most of the updates to OS X El Capitan have focused largely on under-the-hood improvements, bug fixes, and security enhancements rather than outward-facing changes, and OS X 10.11.5 is no exception. No obvious feature changes were discovered in the beta, and according to Apple's release notes, OS X 10.11.5 includes bug fixes, performance improvements, and security updates.
Prior to releasing the OS X 10.11.5 update, which has been in testing since April 6, Apple seeded four betas to developers and public beta testers.