The display protection used on the Xiaomi Mi 4 is not Gorilla Glass but something called Concore Glass. What is interesting is that Concore is made by Corning too. The question you must be asking is, What is ConcoreGlass and how is it different from the famous Gorilla Glass?
What is Concore Glass?
In lay man’s language, Concore Glass is as hard, resistant to scratches and damage as Gorilla Glass is. The only difference has to do with the type of display. If you are not technically inclined, this is where you should stop. If your smartphone has Corning ConcoreGlass, it is just as well protected as if it had Gorilla Glass.
The Technical Jargon
Gorilla Glass is used for protecting traditional discrete-cover glass manufacturing. In other words, the protection is implemented on top of the display. On the other hand, with Concore, the protection is a single unit with the display – OGS full screen lamination technique is combined with the glass touch panel, making it possible to make thinner displays.
We have an article explaining all the different Gorilla Glass competitors. You can check it out here: Gorilla Glass competitors: the other screen protection you should know of