The Redmi 1s and the Redmi Note 3G would be receiving updates by the month of march while the Redmi Note 4G would be receiving update in the early February. Xiaomi Mi3, the predecessor of Mi4 is now receiving the MIUI 6 update in India.
Mi3 users will be receiving an OTA(over the air) update for the new OS. Xiaomi claims to have made MIUI 6 less distracting and its definitely something better than the MIUI 5.
Key features of the MIUI 6 include Motion, Colour Content, Customization and Security. Xiaomi has also introduced animation to some apps like Clock, Weather, and Device unlock, etc.
Share with us your experience as soon as you'll recieve the updates... Awaiting them :)