Approximately none of the iOS APIs have been adjusted for Swift yet.
Also, at least for Swift 1.0, they won't be. Swift does not guarantee a stable ABI right now or for 1.0. They guarantee binary compatibility with the OS, and ABI compatibility with any application frameworks that are compiled alongside the application (because, well, those can't change), but no compatibility between frameworks and applications. The only way to get that compatibility is to stick to Obj-C APIs (or, well, pure C APIs, but that's no better).
What this means is system frameworks will not be able to take advantage of things like generics or multiple return types until sometime in the future, past Swift 1.0. Of course, they couldn't justify doing that today anyway, because they need to maintain Obj-C compatibility for all of the Obj-C code that still exists.
Also, at least for Swift 1.0, they won't be. Swift does not guarantee a stable ABI right now or for 1.0. They guarantee binary compatibility with the OS, and ABI compatibility with any application frameworks that are compiled alongside the application (because, well, those can't change), but no compatibility between frameworks and applications. The only way to get that compatibility is to stick to Obj-C APIs (or, well, pure C APIs, but that's no better).
What this means is system frameworks will not be able to take advantage of things like generics or multiple return types until sometime in the future, past Swift 1.0. Of course, they couldn't justify doing that today anyway, because they need to maintain Obj-C compatibility for all of the Obj-C code that still exists.