Apple has upscaled the glass on the front too. It now says the iPhone 6S Plus now has the strongest mobile phone glass around, a clear suggestion that it's better than the Gorilla Glass 4 we see in quite a lot of phones these days.
I cracked my iPhone 6 which I got a year ago, it's whatever I'm going to upgrade when the 7 comes out. Plus it's only cracked on the corner and not the actual screen