In the United States, Kit Kat is owned by Hershey's while the rest of the world gets these treats made by Nestle. As a result, the US doesn't always have all of the flavors everyone else gets, but we're finally getting one of the more coveted ones: Mint Chocolate.
Starting in December 2019, Mint + Dark Chocolate Kit Kat Duos will be available in retailers nationwide. This is the first of several different Duo flavors that Kit Kat USA plans to be releasing in the near future. The Mint Chocolate Duo flavor works by using dark chocolate for the lower half of the Kit Kat and a mint creme on top.
Kit Kat USA is making this their first flavor release in over a decade, and has confirmed that they plan to be making more in the future. Whether that means we'll finally get to taste trendy global varieties like Ruby Chocolate remains to be seen.