MIUI 8 Chinese Beta build and Global Alpha build is now available for the Xiaomi Mi 5, Mi 4, Mi 3, Mi 2s, Mi 2 and Mi Note. You can just head over to the source link to download the update file and flash it based on the tutorial here.
The Chinese beta ROM for above devices is already available to download for above mentioned devices alongwith the Mi Max and a developer ROM is also scheduled to arrive in June 17th which would add support for the Redmi Note 3 and other devices including the Mi 4c and Mi 4s. MIUI 8 is a major design change for the company, apart from the big dollop of color there is a whole new notification system in place where the quick toggles and notifications from various apps occupy a single page, like stock Android.
There's a new improved Gallery app, Wallpaper Carousel, New Power Saving mode and a lot more which you can read about here.
Most of the stock Xiaomi apps have also been redesigned with performance improvements in tow. Now, just a word of caution, this ROM is not meant for prime-time and is only available to select developers who have been chosen on the Forum for testing.
Update: MIUI 8 Global Beta ROM now available for Redmi Note 3, Mi 4i, Mi 3/4, Redmi 2 Prime and others. Learn more on installing it on your Xiaomi smartphone.
Source: MIUI Forum