Amazon has announced via its Help & Customer Service page that its music storage subscription plans will be discontinued starting from January 15, 2018. If you are planning to subscribe to the music storage service of Amazon, the move means that you must sign up for the subscription plans or upgrade your current storage plan if you are an existing user before the above-mentioned date. Keep in mind, though, that these changes affect only the music files you have saved on Amazon's servers so that they can be played via Amazon Music. In other words, your MP3 files or Prime Music content purchased directly from the Amazon store as well as your Music Unlimited libraries won't go away from your Amazon Music storage plans once the update takes effect early next year.
Quite recently, on December 18, Amazon also removed the ability for PC and Mac users to store music on Amazon Music, though the ability to play and download music that has already been uploaded to Amazon's servers will stay in place until January 2019. What's more, if you're a premium subscriber, Amazon will still allow you to upload music to its servers or renew your subscription plan over the long term. It should be noted that paying subscribers have the ability to store as many as 250,000 songs on the Amazon Music app. As a matter of course, Amazon won't allow you to renew your subscription once your existing storage plan runs out without being reactivated. That means you will no longer have the ability to upload music through the Amazon Music tool once your subscription expires, though your purchased content will remain stored at no cost on Amazon's servers.
It's also worth bearing in mind that once your subscription plan has ended, additional songs on top of your first 250 songs will no longer be available to you via the service, as those pieces of music content will be removed and only 250 songs will remain on your Amazon Music storage. Additionally, those remaining pieces of songs will be available for download and playback for one more year following the expiration of your plan, after which those content will be removed from Amazon's servers.