Today, Josh Holmes, the creative direction at 343 industries tweeted a teaser picture. Shown above is a screenshot of Halo 4's co-op (apparently), though there's nothing in there to suggest this to be the case outside of Holmes' tweet. This is all it said:
Campaign takehome coop action!
So, uh, take from that what you will. It looks like a jungle or something in there though.
Halo 4 is reported to have 4 player co-op for the campaign, and the episodic multiplayer DLC (called "Spartan Ops") will also include co-op.
This latest screenshot is just one of a few newly released details about Halo 4, the last of which was the reveal of the game's button layouts. We'll be sure to keep you up to date with the latest details as they become available.
Halo 4 releases on November 6th, which also happens to be a couple of days after election day.