Following in the footsteps of the Galaxy S6 and S6 Edge on T-Mobile, Android 5.1.1 is now coming to the Un-carrier's Galaxy S5. The phone's support page shows that the goods have started going out under software version G900TUVU1FOF6.
According to the provided changelog, anti-theft features accompany 5.1.1's various bug-fixes. Users can wait for the update to arrive over-the-air or install it manually using Samsung Kies or Smart Switch for PC. The folks over at SamMobile have made the firmware available for direct download. If you choose to go that route, instructions are listed on the same page.