Welcome to iMore!
From Apple:
Availability
A preview release of Swift Playgrounds is available today to Apple Developer Program members as part of the iOS 10 developer preview and will be available with the iOS 10 public beta in July. The final version of Swift Playgrounds will be available in the App Store for free this fall. Swift Playgrounds is compatible with all iPad Air and iPad Pro models and iPad mini 2 and later running iOS 10. For more information including videos, images and demos, visit, apple.com/swift/playgrounds.