Preview at WWDC likely in June, followed by September launch.
Apple Seeds Fifth Beta of iOS 9.3.3 to Developers and Public Beta Testers
The fifth iOS 9.3.3 beta update can be downloaded from the Apple Developer Center or over-the-air with the proper configuration profile installed.
As a minor 9.x.x update, iOS 9.3.3 features under-the-hood bug fixes, security enhancements, and performance improvements to address issues discovered since the release of iOS 9.3.2. No outward-facing changes or obvious bug fixes were discovered in the first four betas of iOS 9.3.3.
iOS 9.3.3 beta 5 comes following the developer launch of iOS 10, a new version of iOS that will be released to the public this fall, with the second developer beta of iOS 10 having launched just yesterday. iOS 10 includes features like a redesigned Lock screen experience, a revamped Messages app with its own App Store, a Siri SDK for developers, a new Home app for controlling HomeKit devices, a redesigned Apple Music app, and more.