LG G3 - QI Charging

Looking for some help. I want to get the LG G3 in the next few days. As I understand it, the US variation does not offer QI charing built in, but is available if you get a replacement back or the circle case. My question is what the model designation of the US Version (specifically Sprint) is. I've googled but can't seem to find. Want to order one and have found sites that offer these replacement backs, but need to know the model.

Thanks for the help