This has been rumoured for weeks, received an email from Songza today announcing that it's now official.
Songza is a fun way to select a playlist based on time of day, activities, your mood, the weather, etc. Google Music doesn't have anything like it currently. Beats has something similar, but Songza, IMO, works a good bit better than Beats' method.
Google sure didn't pay $3 billion for Songza.
Estimates I've seen are $15 million, give or take.