As expected, the new tier offers 50 million tracks with a CD-quality bitrate of 16 bit/44.1kHz (Amazon refers to these as HD tracks) plus millions more in 24bit and up to 192kHz (which Amazon refers to as Ultra HD).
The service is now live in the UK, US, Germany and Japan. It costs £12.99/$12.99 a month for Prime subscribers, or £14.99/$14.99 if you don't have Prime. If you're a current Amazon Music subscriber, you'll need to pay an additional £5/mth to get access to the HD tier.
There's also a launch deal to wrap your ears around: Amazon Music subscribers can get 90 days of Music HD free, while new subscribers will get a free 90-day trial.
The service will automatically offer the best quality stream available depending on your situation and device. Albums available in Ultra HD include Kendrick Lamar's Alright and St Vincent's Digital Witness.
Musician-turned-tech-evangelist Neil Young said in a statement: "Earth will be changed forever when Amazon introduces high-quality streaming to the masses. This will be the biggest thing to happen in music since the introduction of digital audio 40 years ago."
Amazon's top tier undercuts streaming rivals Tidal and Qobuz, so that sound you hear is a gauntlet being laid down. Will it be able match them for quality, though? Prepare yourselves for an in-depth What Hi-Fi? First Test. coming soon.
See our Amazon Music Unlimited review
See our Tidal review