Halo 5 is getting a massive update next week titled the Cartographer's Gift. Building the multiplayer experience, this will add a ton of new content to the game and the best part is that it's free to everyone.
The most noteworthy addition is that of Forge which was absent for the initial release of the game. On top of that there are four new maps coming, two for Warzone and two for Arena. There are also a ton of new REQ pack items launching alongside. To visualise it, take a look at this infographic.