Xiaomi released its first iterations of the Mi Max line in 2016, and they have received regular software updates ever since. However, the OEM has announced that the Mi Max and Mi Max Prime will see its final stable build in April 2019. It will be MIUI 10.3 based on Android Pie.
https://www.notebookcheck.net/Xiaomi-will-cease-official-software-support-for-the-Mi-Max-and-Mi-Max-Prime-in-April.412106.0.html