When are they going to let us do this? Why haven’t they yet? I remember doing this in Halo 3 and it was great fun. I’d like to be able to do this in Halo 4!
? You can play Campaign Co-op online
Yeah, the 1st thing I did back in November last year was run through campaign co-op, even before I looked at it solo 
There will be no online co-op matchmaking in Halo 4, but you can play co-op online in a party.
I know this works with two players, but does anyone know if Halo 4 supports 4-player co-op?
Yes it supports 4 player co-op
I mean Campaign MM I think, like in the nature of Spartan Ops.