MIUI 9 is a fully optimized Android based custom ROM and offers faster and smoother experience to users. Dynamic resource allocation, intelligent CPU allocation, optimized haptic feedback and optimized thread scheduling turns it into a fast and responsive OS.
The MIUI 9 also features Smart assistant (lets you search for almost anything within your device), universal search (powerful search engine that can differentiate your image like you do by typing in keywords), Smart app launcher (suggest apps based on what is on your screen), Split-Screen multi-tasking, and more. The ROM has also some visual changes. Xiaomi has also announced MIUI 9 update schedule for Redmi and Mi devices. The update is scheduled to release in three phases for most devices. Newest devices of 2017 will get the update first and other devices will get in the second and third phases. MIUI 9 update scheduled release on August 21, 2017 for following devices: MIUI 9 update scheduled release on August 25, 2017 for following devices MIUI 9 update scheduled release on September, 2017 for following devices: (Source 1, 2)
