It has nothing to do with the Rx standards. K/N has direct interop with Obj-C, not Swift. Going the other way, it annotates it's header to make the classes feel nice from Swift. But for direct interop, RxSwift isn't usable from Obj-C (90% sure on that), so K/N won't be able to see it (assuming you wanted to use it in Kotlin). You'd have to add some bridging somewhere (possibly Obj-C)