More specifically, there's the iOS 7.1 to 8.0 API Diffs: https://developer.apple.com/library/prerelease/ios/releaseno.... Note that a huge number of the changes are just small changes to argument lists (there are a gazillion of these in Accelerate, filling the top chunk of the diff doc) and a number of other change come from the switch from (id) return types to (instancetype) in init: methods. Also, getter and setter methods have been replaced with properties in many classes, which doesn't break any existing code, but generates changes in the API diffs.
More specifically, there's the iOS 7.1 to 8.0 API Diffs: https://developer.apple.com/library/prerelease/ios/releaseno.... Note that a huge number of the changes are just small changes to argument lists (there are a gazillion of these in Accelerate, filling the top chunk of the diff doc) and a number of other change come from the switch from (id) return types to (instancetype) in init: methods. Also, getter and setter methods have been replaced with properties in many classes, which doesn't break any existing code, but generates changes in the API diffs.