Preview at WWDC likely in June, followed by September launch.
Apple Seeds Fourth OS X El Capitan 10.11.1 Beta to Developers and Public Beta Testers
The new beta is available through the Software Update mechanism in the Mac App Store and through the Apple Developer Center.
OS X 10.11.1, like iOS 9.1, includes support for a range of new emoji like cheese wedge, taco, burrito, popcorn, middle finger, unicorn head, and more. New emoji were introduced in the first OS X 10.11.1 beta. Subsequent betas have not included any other outward-facing changes.
It is unknown what the first update to OS X El Capitan will bring aside from updated emoji, but as a minor .1 update, it's likely to focus primarly on bug fixes and performance improvements for issues encountered following the operating system's official release. According to Apple's beta release notes, OS X 10.11.1 offers stability, compatibility, and security improvements.