A day ago Galaxy Note 9 already received stable One UI/Android Pie update in the US on AT&T network. AT&T is the first carrier in the United States to release the Android 9 Pie update for the Samsung Galaxy Note 9.
The latest update brings January 2019 security patch for the Note 9 users. The software version is getting bumped to N960FXXU2CSA2/ N960FOBE2CSA2/ N960FXXU2CRLT. The size of update 1512.76MB. Keep in mind the size of the update is big and make sure you have enough storage.
If you own an EE Galaxy Note 9 and reside in the UK you can check if the update is available by going into the Settings » Software update menu and tapping the Download updates manually option.