Swift 4 is now officially released! Swift 4 builds on the strengths of Swift 3, delivering greater robustness and stability, providing source code compatibility with Swift 3, making improvements to the standard library, and adding features like archival and serialization.
You can watch a quick overview of it by watching the WWDC 2017: What’s New in Swift presentation, and try out some of the new features in this playground put together by Ole Begemann.
