Samsung pitched Milk Music this spring as a totally free music service exclusive to its devices, but slipped in at the end that it might not be free forever. You can still stream tunes for free without ads (or so the description says), but the new update to Milk adds the expected $3.99 monthly subscription for additional features.
You'll have to sign in with a Samsung account to even have the option of upgrading.
Samsung's Milk Music Update Adds $3.99 Premium Subscription Option was written by the awesome team at Android Police.