From Lattner: "While our community has generally been very kind and understanding about Swift evolving under their feet, we cannot keep doing this for long. Wh

From Lattner: "While our community has generally been very kind and understanding about Swift evolving under their feet, we cannot keep doing this for long. While I don’t think we’ll want to guarantee 100% source compatibility from Swift 3 to Swift 4, I’m hopefully that it will be much simpler than the upgrade to Swift 2 was or Swift 3 will be." https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160125/007737.html https://lists.swift.org/pipermail/swift-evolution/Week-of-Mo... Swift 4 won't have anything like Swift 3's Cocoa renaming. It'll be minor language changes. ABI stability and source compatibility should start with Swift 4.