https://www.gamespot.com/articles/far-cry-5s-vietnam-expansion-gets-a-release-date-a/1100-6459193/

Far Cry 5's first expansion, Hours of Darkness, will launch on June 5, Ubisoft announced today. You play as Far Cry 5 story character Wendell "Red" Redler, but in a different period in time. Namely, Hours of Darkness is set during the Vietnam War and follows Red as he finds and rescues his squadmates in the jungle as he fights against NVA and VC soldiers.

Hours of Darkness is playable solo or in co-op, just like the main game, and it also includes "new gear and abilities." There are also two new modes that you unlock after completing the story, the first of which is Survivor Mode. As its name suggests, this is a more challenging mode that limits your loadout. The other mode is Action Movie Mode, which is basically the opposite, as it gives you a "generous" loadout for more action.