Having already been made available in the United States, Germany, France, Korea, and a few other regions, Samsung has finally launched the One UI beta for the unlocked for Samsung Galaxy Note 9 in the US. Till now, the One UI carrying Pie update was available — as beta — only for the Galaxy S9 and Galaxy S9+ in the country.
Apart from Sprint and Verizon (with U1 firmware), no other carrier carries support for One UI beta. It is very likely that in the near future, this will change. As Samsung has never developed a beta program for the Note series of mobile phones, this is a first. The official date for the release of Android Pie is January 2019.
The genesis of One UI is Samsung Experience 10, which has been majorly modified and restructured to produce the final product. With One UI, Samsung is refreshing the whole software experience of the devices, which should help them a lot as they plan to produce next-gen phones like the Galaxy S10 and Galaxy Flex foldable phone, powered by the next-gen processor in Snapdragon 865 (often called Snapdragon 8150).
XDA member Nochlab1 managed to share screenshots of the sign-up page of the One UI beta from the latest Samsung APK+.