An early demo from CNBC:

https://www.cnbc.com/2019/09/17/amazon-music-hd-promises-high-quality-music-difference-hard-to-hear.html

"Maybe I need better headphones, not a cheapo set that came in the box with a phone....The point is: Sound quality is not just about file size..."    : )

David, thanks for posting. I'm hoping Amazon has a deep catalogue and the GUI is easy to use. I have a Lumin T2 streamer dac and expect Lumin will update their software so I can access.

@tuberist  The catalog rivals Spotify's catalog. No MQA (that I know of). The key (for us) will be how the different services adopt and integrate it into their systems. In my case, Roon.
Interesting development.
Will there be a discount for Prime members?
And Spotify will need to follow suit (finally)!!!
Will there be a discount for Prime members?

Yes.
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@david_ten 

Thanks for the info.  This indeed looks promising.  Certainly not the first time Amazon has undercut the market and killed competitors.
You are welcome.

Spotify is still the leader in our markets (Western) with 100 million plus paid subscribers to Amazon's ~ 32 million plus paid.
Got the email today. Over 50 million songs at CD quality. Maybe I'll get that Amazon Prime account after all and experiment. If it is good, it'll disrupt things a bit, and that would be a good thing.

All the best,
Nonoise
I wonder where Amazon is going to go with 3rd party hardware integration. 
Today is the day High Resolution Audio went mainstream. This will do much, much more than "disrupt things a bit." The implications for our hobby are significant.

I’m excited for the wider catalog access, but truly excited for what this means for impact on hardware (major) choices and software support solutions.

Normally you get trickle down, but in this case we will get the opposite...a trickle up effect. Good news for everyone.

As a single example, can you imagine the impact on sales for Audioquest’s Dragonfly Cobalt....or OEM DAC chips...
I have a TIDAL account with a Scott Nixon dac so no hi-rez necessary. Do you think switching over to Amazon is worthwhile? Yes I have a Prime account.
Hopefully the added competition will result in lower prices from Tidal and/or Qobuz.  I don't buy anything from Amazon if I can help it for a number of reasons, so I won't be using their music service even if the prices for other services remain the same or go up.
I have a TIDAL account with a Scott Nixon dac so no hi-rez necessary. Do you think switching over to Amazon is worthwhile? Yes I have a Prime account.

I don’t know which Scott Nixon DAC you have, but if it is only decodes / outputs CD quality I don’t see why not. How you value the other factors related to streaming, I can’t say.

From the Scott Nixon site, for his newer DACs:

"The usb models are not hi-rez, but I really think most listeners don’t need it yet (or ever). For hi-rez I recommend the s/pdif models and a pro-interface or usb/spdif dongle that will output 24/96. The Chibi and TD2.2 will decode 24/96 and output 16/96. There are usb hi-rez models in the works, but will be 4 to 5 times the cost of these offerings."
Hopefully the added competition will result in lower prices from Tidal and/or Qobuz.

@big_greg  It will definitely be interesting to see how Tidal and Qobuz respond. Spotify and Apple also.
I think it's a usb version of the TD2.2. I've had it since 2006 and don't change equipment often. I think I'll be okay.
@digepix  You'll be fine. Either way (for Tidal and for Amazon) you will be limited to CD resolution. Share your findings if you sign up.
Regarding Amazon's files:  "Both types of HD audio will stream as uncompressed FLAC rather than the MQA format used on Tidal."

From Extreme Tech: https://www.extremetech.com/internet/298538-amazon-pulls-the-rug-out-from-under-tidal-with-new-hd-music-streaming-service
Okay hw do I sign up? The website hasn't been helpful.
Here is the link:

https://www.amazon.com/music/unlimited/hd

Please note I'm not affiliated with Amazon. I also don't plan on signing up at present. I'm a happy Tidal and Qobuz via Roon streamer. : )
Usually I'm not too thrilled about Amazon taking over markets, brick and mortar, etc.  And I'm no expert on the economics of this.  That disclaimer aside, it does seem like it will put market pressure on all to stream higher resolution and that is a good thing for the hobby. 

Off to check out the terms. 
I've signed up now trying to figure out how to get it to work on my system. I'm using JRiver on my laptop and bubbleupnp on Android tablet. I'm going load the Amazon music app on to the laptop.  If anyone is successful please post instructions. 
Yes.  Like being able to control the Amazon music on your main computer with an iPad.
I’ve been using Amazon Music Unlimited, and pay $79/year. I control the program with my phone.

HD is $5 more a month.

Free trial for current and existing customers. I’m trying to upgrade now, but the webpage is very busy according to customer service.

I’m looking forward to trying it out
So download Amazon Music on your iPhone or iPad and you can control the new HD Music on your main computer?
Same question.  Can I sit in the listening chair and use my Android tablet to control the laptop that is feeding data from this Amazon service to an external DAC?  (Like JRiver's JRemote)
How does this work ? With Tidal you have an app  if I could stream this 
from my computer through my dac to Ludspeakers  Thst is Hirez 
 not listening through an iPad . Please advise .thanks much.
Already a Prime member.
Looking forward to trying it.

JD
Giving it a 90-day free trial. Angus and Julia Stone have an album in Amazon UltraHD quality - that type of music sounds so good on electrostats (guitars and vocals). I like that Amazon has clearly identified which music (albums/tracks) are in UltraHD (similar to Tidal MQA)! Will give it a listen on music system tomorrow evening. Interested to see how well it integrates with BluOS2i MDC module (built into NAD C-388 integrated), controlled by BluOS Win10 app. Tidal MQA worked very well on the system, now we’ll see if Amazon UltraHD will recognize the account upgrade, play through it - and how it sounds. The Amazon Prime Music app recognized the account upgrade immediately upon opening the app on my outdated Samsung tablet, so likely BluOS will too, especially since there is no ’unfolding’ to be done (like MQA). As I read in this thread, ’UltraHd’ are FLAC files - will be interesting to see how much WAN bandwidth is required. I did notice the afore mentioned UltraHD album downloaded nearly instantly to the tablet, but suspect it’s likely actually downloading in the background; although, I haven’t noticed any lag on the tablet, so that’s good.
I am using the m-control app (bubbleupnp) recommended by PS Audio with their direct stream DAC. I currently subscribe to tidal and qobuz but am interested in trying Amazon HD, just don't know how to get it on my dac. If anyone figures this out, please let me know
will be interesting to see how much WAN bandwidth is required

From GSMArena:

"If you want to stream music, you’ll need at least a 1.5-2Mbps LTE connection for HD quality and 5-10Mbps for Ultra HD. A large data allowance is a must too – a 3 and a half minute song eats up 51MB in HD quality and 153MB in Ultra HD. A lossy track is 9MB."

https://www.gsmarena.com/amazon_music_hd_launches_with_two_lossless_audio_options_in_four_countries-news-39226.php

Note: these figures are not verified.
My initial thoughts were that Amazon might be trying to go after Apple like they have done in the movie market (i.e. Netflix) - maybe go after the audiophile market as a longer-term objective.  For me Roon integration would be essential.
Yes it must offer Roon integration! I use both Qobuz and Tidal. Both services sound different from each other in Roon. Thus far I like Qobuz a little more. It is less aggressive and more relaxed sounding..,warmer.  Others will like Tidal more as this is subjective and system dependent. Comparing the exact same 16/44 recording on both services reveals a sonic difference.  Seems these services have a “sound” beyond the numbers. 
Amazon wants $9.99 from me for a trial. $14.99 after that.
That’s because I did a free trial of the old service. Then cancelled it.
Makes me wonder if I log in on my Node2i, will I get HD?
Of course I'd have to resubscribe
I’m not a prime member
How does it work with Aurender?
@grannyring   Agree. Roon integration is key for me as well. It will be interesting to see how all of this shakes up the streaming marketplace.
Brief early "experience / use" feedback. Might be of help to those just starting out with the service.

Those of you with Bluesound / NAD products will be sitting pretty. : )

https://www.t3.com/news/amazon-music-hd-review
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"If you want to stream music, you’ll need at least a 1.5-2Mbps LTE connection for HD quality and 5-10Mbps for Ultra HD. A large data allowance is a must too – a 3 and a half minute song eats up 51MB in HD quality and 153MB in Ultra HD. A lossy track is 9MB."

Above (posted earlier) verified from multiple outlets. [Quote is from GSMArena]
Pertinent information from Apple Insider:

"HD tracks are 16-bit audio with a sample rate of 44.1kHz, or CD-quality, and an average bit rate of 850 kilobits per second. Ultra HD tracks 24-bit audio with a sample rate of up to 192kHz, and an average bit rate of 3730 kilobits per second. As Amazon points out, most streaming services only offer standard definition quality music, which reduces some of the detail in order to save on file size.

Because the files are lossless, it should be noted that they are significantly larger. A standard song comes in at just around 9 megabytes, where as an HD song comes in at 50 megabytes. An Ultra HD song comes in at 153 megabytes, meaning that devices will be able to hold less music at higher qualities.

This also means that streaming HD and Ultra HD songs will use up more of your data plan, so it's advised that people with lower data caps listen to music via Wi-Fi or download the music for offline listening later.

Additionally, the quality of the music is going to be heavily dependent on how you're listening to it as well. Playing the music through low-quality speakers is going to render a low-quality result."

https://appleinsider.com/articles/19/09/17/heres-what-you-need-to-know-about-lossless-amazon-music-unlimited-hd
In a lazy and totally non-scientific comparison across a couple of my 2nd-tier hifi systems:

Amazon Music "HD" and "Ultra HD" quality levels seem comparable to similar-res audio from Tidal and Qobuz (16-bit/44khz and 24-bit/48kHz). I didn’t compare to Tidal MQA. If anyone thinks they can objectively ’hear’ and distinguish hifi audio ’quality’ differences above 48kHz, or if you don’t but really-think-it-matters, read this: https://people.xiph.org/~xiphmont/demo/neil-young.html. <= the irony is poignant, given Mr. Young’s latest gushing about how "Earth will be changed forever when Amazon introduces high-quality streaming to the masses."

Amazon’s web- and Mac/Win native players are consistent with other services’ apps: a race-to-the-bottom in effective UX and functional design. In an equally non-scientific and lazy study I have the Spotify, Qobuz and Amazon apps tied for dead-last, then Tidal at barely better. All of them suck in various ways.

Amazon is still working out issues in their catalog play-back (wrong tracks behind some albums, no tracks behind some "Ultra HD" albums etc). Catalog curation is also kinda ’wtf?’ in places. No surprise - greed/fear/hubris rushes most consumer digital media services to market. What are free trials for, anyway?
So far so good. I upgraded Amazon to HD and it sounds very good. The interface is different than TIDAL but it shouldn't be too difficult to navigate. My stereo is far from great YBA electronic into Vandersteens with a Scott Nixon dac but for CD quality streaming it's not bad. As I get further into it I'll update.
just started my free trial--initially i find the UI inferior to and less intuitive than spotify but better than tidal. catalog seems deep, if not as extensive as spotify. ultra hd sounds great; hd sounds better than spotify, though it's not a night-and-day difference and there's less ultra hd content than expected. playlists are ok, though not as well-done as spotify--i expect they'll markedly up their game and add content as they gain traction, since amazon is very customer-focused and has long-term vision on their road to world domination.
Only if Amazon have off-line ultra HD. LTE is not reliable at some location and insider building. I would do hard wired streaming at home or off-line on the road. Doing away from MQA is good if Amazon can do 192/24 or at least 96/24. My Oppo HA-1 and 105D can't take MQA.
Logged into Amazon Music on Node2i,  HD option shows up as menu item. When you click on it it asks you to sign up
Aurender says they are in contact with Amazon and will update in the coming weeks.
@cedargrover  Thanks for that update. It's great news!