Finally, after a long wait, LG G3 AT&T d850 is managed to get Official Cm13 rom for now you can Update LG G3 (D850) ATT to marshmallow by installing official CM 13 nightly for LG G3 ATT D850.As of now first official cm13 nightly is released by the cyanogenmod team based on latest Android marshmallow 6.0.You can download cm13 official nightly for LG G3 D850 from official CyanogenMod website from the provided in the download section below.Download official cm13 for LG G3 D850 At&T from below link.
As the rom is new and no one yet tests it, so we request your to test it out and report in the comment section.As this is first cm13 nightly, there may be bugs in it.I refer you to make the backup of your current rom before flashing this rom.Let’s start the guide on How to install Official CM13 rom on LG G3 AT&T D8550.
#How to install Official CM13 rom in LG G3
1.Download official CM 13 nightly for LG G3 D850 .and the appropriate Gapps 6.0 package from the link given below Copy it in your in your device.
2.Now place the Official Cyanogenmod 13 rom and gapps 6.0 zip file in sd card.
3.Now reboot to Recovery mode.
4.Then flash CM13 rom and Gapps 6.0 from a recovery in it.
5.Now Clear Cache and Clear Data.
6.Reboot your device.Done! You just flash Official CyanogenMod 13 rom in your L.G G3.
Enjoy Android Marshmallow 6.0 !.