The newer build of Lollipop (Android 5.1.1) with software version G900TUVU1FOF6 finally released for T-Mobile variant of the Galaxy S5, this is good news for its users, as some glitches that they experienced before will soon go away after installing this official OTA update. As we know, the initial release of Lollipop (Android 5.0) has some bugs such as memory leaks, and the performance is not better than the official KitKat release.
You should get an update notification now, you can also force the phone to check the update by going to update options on Settings -> About device. If your T-Mobile Galaxy S5 has been rooted with custom recovery like TWRP, you can also download the flashable stock ROM zip that available at xda. However, this will trip the Knox counter (Knox 0x1). If you are familiar with FlashFire app by Chainfire, you can use it to flash the stock ROM, in contrast with TWRP, FlashFire will not trip the counter (Knox 0x0).
Although the update brought many improvements, but there’s no way to root this Android 5.1.1 for the T-Mobile Galaxy S5 for now. This was confirmed by dev from xda – muniz_ri, a dev who had discovered a method to retain root on several Samsung devices after it get updated.
He said that there’s no go for official Android 5.1.1 (OF6) updates, and SuperSU likely will need updating to cooperate with the new OTA update (G900TUVU1FOF6).
If you prefer root access over the most recent official update, it looks like you have to wait until the root method for Android 5.1.1 found out.