The Mate 9 and Mate 9 Pro had their Oreo beta testing programs opened a few months ago, so it comes as no surprise that both devices are finally getting stable Oreo rollouts, with the P10 and V9 to follow soon.
https://www.notebookcheck.net/Mate-9-and-Mate-9-Pro-set-for-stable-Oreo-release.268360.0.html