The recode[0] and cnet[1] articles have some additional details that people seem to be asking about here.
> In a briefing this week, the company promised it will be closing gaps between the two services over the next month, so Google Play Music members don't lose the features they've grown accustomed to, including a cloud-based MP3 storage locker.
* Anyone paying today will be grandfathered in at their current price into Youtube Premium. If you aren't paying, Music will cost $10, Premium will be $12 for new subscribers.
> In a briefing this week, the company promised it will be closing gaps between the two services over the next month, so Google Play Music members don't lose the features they've grown accustomed to, including a cloud-based MP3 storage locker.
* Anyone paying today will be grandfathered in at their current price into Youtube Premium. If you aren't paying, Music will cost $10, Premium will be $12 for new subscribers.
[0] https://www.recode.net/2018/5/16/17363334/youtube-music-laun...
[1] https://www.cnet.com/news/youtube-music-is-googles-latest-st...