Download links for a Spotify app for iOS have appeared on its community website. In addition, a Redditor also claims that there is also a WatchOS variant of the same in beta. However, the app is still in beta and does not much more beside the control of playback using the streaming service.
https://www.notebookcheck.net/Spotify-now-reportedly-working-on-Apple-Watch-app.355306.0.html