Microsoft has decided that Spotify is probably quite a lot better than its own service, Groove Music, and decided to kill off the latter at the end of this year.
The Music Pass subscription and individual purchases will stop working at the start of 2018, although the Groove Music app will remain for playing music stored locally or on One Drive.
The good news is that Microsoft has partnered directly with Spotify to make this process less painful, and will allow subscribers to migrate their playlists and music collections to Spotify. You'll have until the end of January to sort everything out.
Apparently there will also be some refunds and free trials of Spotify Premium for certain users, so check out the Microsoft website for details.