Huawei had previously outlined plans to update its late-2016 and early-2017 flagships - the P10 and Mate 9 series - to Android 9.0 (Pie) by March 2019. It appears the OEM is finally ready to make a start on these commitments with an update for Mate 9 users in China. This version of Pie includes new features such as Huawei HiVision.
https://www.notebookcheck.net/The-Huawei-Mate-9-is-receiving-an-update-to-Pie-in-China-now.401221.0.html