The co-op mode in Halo Infinite won't have online matchmaking.
Players of the recent beta noticed matchmaking wasn't available, but Xbox has confirmed to GamesRadar the feature won't be in the final release.
"Online matchmaking will not be available with final co-op," said an Xbox representative. "We encourage you to continue to use the Halo LFG and the new Discord voice call feature on Xbox to find players to party up with as you continue playing the beta."
Clearly, the co-op mode is designed for friends to team up and blast Grunts together, rather than playing with random others.
That does mean if your friends don't have access to the game, you may need to scour LFG (looking for group) message boards in order to play co-op.
That quote is also a nice little bit of promo for the new Xbox and Discord voice chat integration.
On the flip side, online play is often rife with toxicity and abuse, so restricting co-op mode does mean players will be safe from harassment from randoms online.
Developer 343 Industries is targeting an August release for the full Halo Infinite co-op mode.