The short answer is neither.
The long answer is: technically, Halo Anniversary is not changing multiplayer, but it kind of is. Bungie (the developer of all the Halo games, but the C&C title Halo Wars) no longer runs multiplayer, nor will it develop any more Halo games. The new studio in charge of the future of Halo and multiplayer is 343. A lot of Halo fans have really despised aspects of Reach multiplayer, but Bungie just ignored them. 343 is launching a title update for Reach's multiplayer making changes to the things fans have complained a lot about. Needless to say Halo Anniversary does not have its own multiplayer matchmaking (like ODST did not have its own multiplayer matchmaking), although it has a seperate engine, Reach maintains multiplayer.
Microsoft's goal for the Halo franchise is 1 game a year. As of now the main multiplayer is only changing as games of the main cannon are released.