https://developer.apple.com/library/prerelease/content/documentation/DeveloperTools/Conceptual/WhatsNewXcode/introduction.html
Compatibility
Xcode 8 beta requires a Mac running macOS El Capitan version 10.11.4 or later. It includes SDKs for iOS 10.0, watchOS 3.0, macOS Sierra version 10.12, and tvOS 10.0.