Can apps created with Xcode 8 / Swift 3 be installed on an iPhone 4 device running iOS 7? Does Xcode 8 / Swift 3 support all iOS 7 devices?
Is there specific documentation detailing what is and isn't compatible that answers this question?
It appears Xcode 8 doesn't seem to ship with an iPhone 4/4S simulator. Currently my experience is that apps created with Xcode 7 / Swift 2 can be installed successfully on iPhone 4S running iOS 7.
EDIT: I've now done some testing with "interesting" results: Do Xcode 8 Swift 3 apps run on iOS 7 successfully?