Three in the booth itself, and then CC Sabathia is sitting in the front row somewhere with a headset on chiming in wherever they throw it to him. NBC, in its first season doing MLB in a while, has opted to go with one p-b-p guy plus a non-permanent rotating crew of color commentators, one each with ties to the two teams playing that particular day. So Zeile is 'representing' the Mets for today with Geoff Blum carrying the flag for the Astros.
For decades this sport managed to present the game, even on network telecasts, almost exclusively on two man booths: Curt Gowdy/Tony Kubek, Scully/Garagiola, Buck/McCarver. Keith Jackson/Cosell, etc.. Now it seems that none of them can survive with fewer than four.