Official device list is as Follow, but not sure if Xiaomi.eu will also give all of them Miui 9;
Mi 6, Mi 5s Plus, Mi 5s, Mi 5c, Mi 5, Mi 4S, Mi 4c, Mi 4, Mi 3, Mi 2/2S, Mi MIX, Mi Max 2, Mi Max, Mi Note 2, Mi Note/Pro, Mi Pad 2, Mi Pad 1, Redmi Note 4X (MTK), Redmi Note 4X (SD), Redmi Note 4...