AT&T starts rolling out Android 9 Pie for Samsung Galaxy Note 9
Galaxy S9, and S9+ received the update a few days ago. In any case, if you own an AT&T Galaxy Note unit, you should now be eligible for an Android 9 Pie update.
Keep in mind that this is a fairly sizeable update, so be prepared to wait and make sure you have enough storage. According to a thread on reddit, the update weighs in at around 1.85GB, and it's only available from AT&T.
If you're looking to update your Samsung Galaxy Note 9 via T-Mobile or Verizon, you'll have to wait a while longer since nothing has popped up for these models yet. But the bad news is unlocked units are once again getting a major Android update after carrier-bound phones.