Finally AT&T started seeding Stock Marshmallow update to LG G3. The Android 6.0 Marshmallow firmware carries security patch for the last month with build number MRA58K along D85030K software version, usually carriers took delay as compared to unlocked devices for releasing firmware updates as they put their own apps inside firmware and then release it after multiple testing. The Marshmallow update for AT&T LG G3 is also packed with amazing new features including Doze Mode, and better apps permission further you would be on latest firmware. We are just waiting for the KDZ file, as soon as it becomes available we will update the link so that you can install it manually without waiting for the OTA.
LG Flashtool Method (Manual process): To manually update AT&T LG G3 via LG Flashtool requires Marshmallow firmware KDZ files [will be available soon] So lets begin with the OTA method.
Update D85030K Stock Marshmallow on AT&T LG G3 via OTA
To update AT&T LG G3 on Android 6.0 Marshmallow D85030K firmware you don’t need to download multiple file for it, just you need your device and the working internet connection. You must also remember that OTA process works only on Stock devices which means your device is no longer rooted while you searching for latest firmware via OTA. If you think your device is rooted then don’t waste your time switch to alternative firmware update processes or if possible un-root it and then give it a try. But we don’t recommend you to get stuck in such a long un-rooting process just manually if the download link is available. If you think you are all set to go, then
Go to device Settings >> tap on About device >> Software updates.
Now tap it to check the latest available firmware. Upon it’s availability you will be prompted about the update, now what just tap “Download Now” to instantly download the firmware or “Download later” if you wish to download later. Some times it depends on the region too for example, if the update is released for a specific region but you are not present there it will take some delay until firmware update reaches that region.