T-Mobile rolling out Android 9.0 Pie for Samsung Galaxy Note 8
As always, T-Mobile is deploying this on a scheduled daily limit to prevent network congestion, which means it will not be available to everyone at the same time. However, by the end of the next week, all T-Mobile Galaxy Note 8 owners should receive the update, so make sure to check back again the next day if it doesn't show up on your phone immediately.
As far as the contents of the update go, T-Mobile is a bit vague, but it does mention that besides Android 9.0 Pie, users will get “various bug fixes and system improvements.” Also, it would make sense for the update to include the March security patch as well.
Now, in order to make that you'll be able to download the update, make sure that your Samsung Galaxy Note 8's battery is at least 50% charged and that you have 1.8GB storage available. To check whether or not you can update to Android 9.0 Pie, head to Settings / Software update / Download update manually.