https://wccftech.com/samsung-galaxy-s9-and-s9-get-android-pie-on-t-mobile/

Barring T-Mobile, every one of the ‘big four’ carriers in the US rolled out the much-awaited OneUI-based Android Pie update for the Samsung Galaxy S9+ and S9 Plus (and the Galaxy Note 9 in some cases). Today, T-Mobile joins that list. The ‘un-carrier’ just released the Android Pie update for the Galaxy S9 and Galaxy S9++.

As far as the actual update is concerned, you’ll get Samsung’s One UI interface that brings forth a host of changes and features. You get a system-wide Dark Theme, a redesigned UI for several apps such as Samsung Messages, a redesigned camera app and a lot more. Here is the full changelog: