The screen on my Galaxy S6 doesn't have scratches after one month of intensive usage without a screen protector. And by intensive I mean letting my girlfriend use it with her long nails, my 8 year old nephew plays games on it with his greasy and crumbly fingers from eating potato chips and peanuts. I put it in and out of my pocket a lot of times a day, also during cycling with a lot of friction. Sometimes the screen comes in contact with things like hair combs, remote controls and those kind of things. I have inspected my screen under all kinds of lighting and not a single hairline scratch or whatsoever.
A friend of mine used his Galaxy S4 for two years naked without a scratch on his screen. And believe me, there are enough people who are able to find even the smallest hairline scratches. But if it they aren't there, they aren't there. The Gorilla Glass 4 on my S6 feels great and already came through the durability test after one month, and I'm positive that further down the line there's a big chance that the screen will stay pristine. Here are a couple of pictures of my S6's screen, I know it's still not 100% proof that it's scratch free, but trust me it really is
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