Samsung is making two different Galaxy S8 sizes next year, new rumors from its home country of South Korea are saying. One, called Galaxy S8, will have a display around 5 inches in size, just like its predecessor - the Galaxy S7. The other phone, however, will go where Samsung hasn't gone before when it comes to the screen size of a flagship. The Galaxy S8 Plus is rumored to arrive at the same time as the S8 (and sharing most of the specs), but sporting a 6-inch AMOLED panel. Past reports have mentioned both phones would have curved displays, and this new speculation doesn't contradict...
Source: http://www.gsmarena.com/6inch_samsung_galaxy_s8_plus_is_on_the_way_alongside_5inch_s8-news-22345.php