It should be at least Gorilla Glass 2 as its not like the first one is available anymore unless you buy an old device. Gorilla Glass is NOT scratch proof, shatter proof, or anything magical. It will get scratched eventually. There is a newer Gorilla Glass 3. That isn't magical either. Corning claims its xx % better at reducing scratches and surviving from a fall without cracking and uses their own skewed test methods, but glass isn't like looking at the latest processor that comes out every six months that is smaller, faster, and kills in benchmarks. It's...glass. Hasn't changed in eons. You can't just improve it every year. Lots of crazy spec heads get angry because the 1520 doesn't have the 3rd generation version, but all the generations are largely the same and the numbers don't mean anything. Even worse is the new structure may have improved one facet of its durability, but significantly reduced another. Like when a drug company changes the formula for one of their drugs that recently went generic when the patent expired, gives it a new name, and charges you up the wazoo even though the change is insignificant or even more detrimental than the original.
The glass doesn't matter in other words, so don't worry about it. All mid-range to high-end phones all use some form of mineral glass / gorilla glass / dragontail glass that perform about the same and there isn't any breakthroughs or must have glass panels. Glass is not invincible.