On this site about its recent launch it mentions both version having a 6GB VRAM GTX 1060.
BUT, when i look at it on newegg, it says it's only 3GB of VRAM. I have never seen a laptop 1060 with 3GB of vram. I can't tell if Tom's is off or if newegg is off about the specs. http/www.newegg.com/Product/Product.aspx?Item=N82E16834234295
3 minutes of Googling showed an almost endless stream of vendors (excaliber pc, xotic, amazon, hidevolution, B&H Photo, etc...) claiming it is 6GB.
EDIT: Apparently it (the 1060) is available in either 3 or 6GB versions, and that's what it shows on Newegg as well. Seems odd though...
Indeed i saw that to but on deeper look at newegg, the 6GB 17.3 inch version is only avaible with the SSD version. Drop the SSD and you loose 3GB of vram for some odd reason. Unless you go with the 15.6 inch. It would make so much more sense if Asus would list the laptop on their website for official specs.