In addition to all of the great user facing changes that iOS 9 will bring, it will also add some new functionality for developers to take advantage of.
Apple has unveiled at WWDC 2015 some of the changes that come behind the scenes in iOS 9 that developers will be able to take advantage of. One of the new features is app thinning, which makes apps smaller in size, including just what is needed within the app.
Additionally, Apple has enhanced a number of existing tools, like Metal, SceneKit, and SpriteKit. For gaming they have added GamePlayKit, Model I/O, and ReplayKit. With ReplayKit users can now record and save gaming video, right from their device.