I posted this on another Amazon thread (that already existed), but here's the email I received...
We have some great news for you – going forward, there will be no extra charge for HD as part of your Amazon Music Unlimited subscription.
You will continue to have full access to all of your HD content, but at no additional cost. This change will be reflected in your next billing cycle.
I've been using AmazonHD since they announced it. Ended the Tidal (Masters?) subscription. Tidal was ok, but the focus on Rap/R&B/Pop was annoying. I play it with BluOS products, NAD C388 (with BluOS2i MDC card), and Node2i - they have been great, and both stream at 24/192 while listening through LXmini + OB-subs with either ATI 6012 (class AB) or Hypex FA123 (Ncore class D).
BluOS is great, control either Blu units with phones, tablets, PCs and even group (at will) for whole home (same stream). Also plays nice by voice, with Alexa skill.
Allows access to AmazonHD custom playlists (unlike Denon/Marantz HEOS - which does not). However doesn't allow creation of custom playlists from within BluOS.
Another cool thing is AmazonMusic family plan, which allows multiple (think 6) family member accounts. So each family member can have their own favorites/custom playlists/history/etc. and they're not all mixed into one account. That means I don't have to listen to Pretty Wife's country music when I choose to listen to my UHD favorites playlist! UHD shows as FLAC (BTW). Family plan also allows multiple simultaneous UHD streams being played on any devices. Example: I'm listening to my "Chill Sounds" on 2-ch system, wife's on Sun porch on her phone BT to Edifiers, Son is streaming to IEMs from his phone, Nephew is in basement on the HT system (Denon HEOS) via Echo Dot control.
It's actually very futuristic now that I think about it. A massive catalog (I've never not been able to find a track I've search for), playable in CD+ quality, anywhere an internet connection is available. Tech has come a long way since my early audio years with cassettes and LPs. "Someone go flip the record over." - not!