There's no guarantee that this rumor is true, so as usual take this with a grain of salt. Don't worry; I'm not going to be posting any spoilers since I don't want to know what was written just in case it is true. That said, it is worth mentioning that there are allegations that the ending to Horizon: Zero Dawn has been leaked on 4chan. A thread on NeoGAF popped up earlier today and talks at length about details regarding the game's ending.
These details were apparently derived from a series of mock reviews of Horizon: Zero Dawn which appeared to be in line with known facts that have been revealed from developer interviews and promo materials. Developer Guerilla Games has not commented on these supposed leaks as of yet, but doing so could potentially have harmful effects. In a way, they are caught between a rock and a hard place, where commenting on them or having them removed could confirm their legitimacy.
So in this case, the best course of action for Guerilla Games is just to sit tight, and let fans decide for themselves whether or not to click on it. If you don't mind spoilers and wish to read them, you can do so by heading over here.
Horizon: Zero Dawn releases exclusively for PS4 on February 28th, 2017.
