The title is not a mistake. rx.Observable from RxJava 1.x is a completely different beast than io.reactivex.Observable from 2.x. Blindly upgrading rxdependency and renaming all imports in your project will compile (with minor changes) but does not guarantee the same behavior. In the very early days of the project Observable in 1.x had no notion of backpressure but later on backpressure was ...