Preview at WWDC likely in June, followed by September launch.
Apple Seeds First OS X 10.11.5 El Capitan Beta to Developers
The new OS X 10.11.5 update can be downloaded through the Apple Developer Center.
We don't yet know what improvements the fifth update to OS X El Capitan will bring, but like prior updates, it's likely to focus on security enhancements, performance improvements, and bug fixes to address issues that have been discovered since the release of OS X 10.11.4. We'll update this post with any changes that are discovered in the beta.