Quiet will be added to Metal Gear Online along with new maps in an upcoming content update.
According to an announcement made by Konami during Tokaigi 2016, Quiet can be selected as a unique character.
Unique characters such as Quiet, per Gematsu, are selected as a mission setting prior to beginning a game round.
Once selected, the character is assigned to a random player in the team for the whole round.
As for the new maps, there will be three total and are Azure Mountain, Coral Complex and Ruse Palace.
A release date for the new content wasn't provided.