From a quick look, it is on Bandcamp, for those that would rather have it DRM free (FLAC, MP3 and derivatives):
https://garoad.bandcamp.com/album/va-11-hall-a-prologue-ost-sounds-from-the-future
It's also on ITunes (only AAC and MP3), but worth noting getting to the store page is a bit cumbersome even with the link:
https://music.apple.com/us/album/va-11-hall-a-prologue-orignal-soundtrack-sounds/1190726465