It's probably just a placeholder, but US retailer Walmart has listed Halo for Xbox One, suggesting an October 1 release date. What the listing also offers is a possible look at the front cover for the next Halo game, although that too might be a placeholder.
What this listing does do is conflict with existing reports that suggest Halo 2: Anniversary is in the works and that Halo 5 is coming in 2015. Somebody's right, although we might have to wait a while before we find out who.