Go to Microsoft's official Xbox One Wireless Controller product page. Go ahead, I'll wait. Now, if you scroll down, you'll notice on the right side under additional features that up to eight wireless controllers can be connected at once to the Xbox One. As one of my favorite childhood characters Winston Zeddmore (portrayed by Ernie Hudson) would say, "That's a big Twinkie."
As you probably know, the Xbox 360 can only support up to four controllers. I'm not sure how big of a bragging right supporting eight controllers is, since I can't imagine any games actually supporting that. When will you ever have eight people in a room playing one game on a single screen? At least there's potential for eight people at once. Maybe Fusion Frenzy 3 is in the works?
Another notable feature is that the Xbox One controller has a wireless range of 30 feet.
Just for comparison, The PS3 supports seven controllers, but no games utilize that. ***EDIT: It has been pointed out to me that two games, in fact, support 1-7 players: FIFA and NHL.***
There's no word on how many controllers the PlayStation 4 will support.