Apple has just released iTunes 12.5.1 in the Mac App Store, just head of its public iOS 10 release.
This updated version comes with an all-new Apple Music design (to match the upcoming update in iOS 10), support for iOS 10, plus support for Siri to play music. The update will also support picture-in-picture, so you can watch videos while you multitask (a feature from macOS Sierra).
You can download the latest update by going to the Updates tab in the Mac App Store. Update: PC version now available as well.