Preview at WWDC likely in June, followed by September launch.
Apple Releases Second iOS 9 and OS X El Capitan Public Betas
Beta testers who have signed up for Apple's beta testing program and already have the first public betas installed can update over-the-air for iOS 9 or through the Software Update mechanism in the Mac App Store for OS X.
The iOS 9 beta includes the return of Home Sharing for music, which was removed in iOS 8.4, and it's the first beta that supports Apple's new iPod touch. Other changes include a new look for Handoff in the app switcher and a bug fix that once again allows the volume buttons on an iOS device to serve as a shutter for the camera. A full list of changes in the beta can be found in our iOS 9 beta 4 tidbits list.
OS X El Capitan beta 4 focused more on performance improvements and bug fixes with few outward changes to the operating system.
Both iOS 9 and OS X El Capitan 10.11 are expected to be released in the fall.