https://www.theverge.com/2019/1/29/18202448/samsung-galaxy-s9-note-9-android-pie-one-ui-update-us-rollout-carriers

Samsung has just begun rolling out a promised update for the Galaxy S9 and S9+ that brings them up to the latest version of Android 9 Pie, and switches everything over to Samsung’s new interface, One UI. And by “just,” I mean “just for Xfinity Mobile customers,” as Android Police notes. That makes for very a limited rollout indeed for the US, though the update has been coming to international customers for over a month.

US customers on other networks (or who have unlocked devices) will need to wait a bit longer. Samsung tells us that “the update for Galaxy S9, Galaxy S9+ and Galaxy Note9 will continue to roll out to other carrier providers in the coming days and weeks.”