T-Mobile's version of the OnePlus 6T has consistently been receiving software updates at a different (read:later) pace than the unlocked model. Today a new one has started making its way to those units sold by the magenta carrier.
It's a 110MB download that enables activating the Google Assistant by holding the power button for 0.5s. If you turn this on this in Settings > Buttons & gestures, you'll need to hold the key for 3s in order to reach the power off menu. The Assistant shortcut is very handy if you have full screen gesture navigation enabled, as that takes away the option of holding the Home button for a bit to achieve the same purpose.
Additionally, the new software comes with an updated camera app, an updated algorithm for the in-display fingerprint scanner, optimized Face Unlock and login for hidden Wi-Fi access points, enhanced unlocking speed with live wallpapers, and improved audio quality. A Play Store download notification issue has been fixed as well.
OnePlus estimates it will take you around 5 minutes to install this release once you've downloaded it. After you do, your phone will be on software version A6013_34_181121.