T-Mobile's version of the Samsung Galaxy Note5 is now receiving a new software update. This brings with it the latest security patches, both from Google and from Samsung. Thus, after you apply this version, you'll be on the May 1, 2017 Android security patch level. Previously, the Note5 was on the March 1 level, so this is a welcome change.
The update arrives over-the-air as you'd expect, and it's a 209MB download. Even with it installed, you're still running Android 7.0 Nougat - no 7.1 here. Samsung's build number for the update is N920TUVU4EQE1.
As always, such an update may take a few days to reach all of the Note5 units sold by T-Mobile. However, if you can't wait you might want to try manually checking for the new release, by going to Settings > About device.