NO ITS NOT!! its not optional, its mandatory, if you don't have the maps you WILL NOT be able to play matchmaking i believe.
And you buy it for the Halo (xbox1) Dashboard and charge you Credit Card, just like you Bought/Downloaded the old maps.
And if you wanna Explore the New Maps April 17th SEND ME A FRIEND REQUEST!! i will Be online playing Halo that day untill they come out, so we can explore them together as soon as they come out.