MIUI 9 was announced along with the Xiaomi Mi 5X last week and its official rollout is starting in a week. The first two phones to get it are the Xiaomi Mi 6 and the Xiaomi Redmi Note 4X and they will only have to wait until August 11. Two weeks after the first dispatch, on August 25, 12 other phones will get MIUI 9. They are the Mi Mix, the Mi Note 2, the Mi 5, the Mi 5s, the Mi 5s Plus, the Mi 5c, the Mi Max and its newer sibling the Mi Max 2, the Mi 4s, the Mi 4c and the Redmi 4X. There will be a third wave of updates come September. That will include some entry level...
Source: http://www.gsmarena.com/xiaomi_mi_6_and_redmi_note_4x_to_get_miui_9_on_august_11-news-26583.php
