Follow these steps to have a toggle for removing all UI elements:
1) Go to: C:\Program Files (x86)\Steam\steamapps\common\global agenda live\tggame\Config
If you have the HRUS installation of the game, the file location is: C:\Program Files (x86)\Hi-Rez Studios\games\global agenda live\tggame\Config
2) Find Tginput.ini and open in notepad
3) Replace all instances of this line:
with this line
4) When you get in the game, press F5 to toggle the hud on and off.
This will remove the default binding of "Show Dev Notes" from the F5 key.
In combat areas, you will be able to "scope" and have no UI / overlay at all. In Dome City, you will have to do all your shots with the "cameraman" near a wall. If you get next to it and face outward, the character will disappear. For certain walls you will need to crouch.