If you live in the US and also subscribe to the premium tier of Spotify, then you will be eligible for a free Google Home Mini unit, while stocks last of course.
The music streaming held this offer last year and now it returns.
Spotify has provided some phrases you can use to control Spotify music on your Google Home:
So get grooving by setting Spotify as the default music player on your device. You can just say something like “Hey Google, play Disco Forever playlist” or “Hey Google, play Party in your Living Room playlist on Spotify.”
Spotify have said you can claim your free Google Home Mini by going to https://www.spotify.com/us/premium/ or https://www.spotify.com/us/family/
Source: Spotify ‘For the Record’ Blog