It looks like Android Version 6.0 (also known as Marshmallow or Android M) is rolling out to all kinds of newer Android devices, and it looks like certain phones from LG are getting it. This is the latest news on Android M Version 6.0 Marshmallow Release Date for LG G5, G4, G3, G Flex 2, G4 Style, and V10 on Sprint, Verizon, US Cellular, T-Mobile, and AT&T.
So when it comes to the LG G5, this is pretty much covered with having Android Marshmallow right out of the box. The next one down the line is the flagship from one year ago with the LG G4, which currently has Android M available for it in Korea. It is reported that here in the United States, the LG G4 has been upgraded if you are a AT&T or Verizon subscriber.
Often, some carriers receive the upgrade before others, so it is possible that those who are on Sprint, T-Mobile, and US Cellular might be getting the Android 6.0 upgrade assuming that it isn't available for an Over The Air (OTA) upgrade already.
So what about the flagship from two years ago with the LG G3? The Lawyer Herald reports that the official 6.0.1 Marshmallow upgrade on the G3 units started rolling out as of March 31. When it comes to carriers in the United States, such as Verizon, T-Mobile, Sprint, AT&T, and US Cellular, this same article states that neither of these companies have released the Marshmallow update to their G3 devices.
However, this was the same source that stated that Verizon started rolling out Android M on the G3. This source also says that once these carriers passed on the upgrade for the G3, so there is some mixed messages transmitted here. From what it sounds like, it seems that the upgrade is on its way to the G3. In fact, if you own a G3, it is recommended that you go to your "Settings" and "System Update" to see if it isn't available, particularly if you are a Verizon subscriber of this device.
Other phones that are going to get the upgrade, according to Tech Radar, include the LG V10, the LG G Flex 2, and the LG G4 c but "there's no official word yet". However, it is apparently "Rolling Out" for the V10, according to the Android Pit, but that is in Turkey, so it might be a while before it hits United States carriers.
There is a recent report from Neurogadget saying that the LG G2 is a flagship that is too old, so it won't get the upgrade, but there is a custom ROM that can be installed for it, and you can click here if you are interested in trying that out for yourself. It would be a good idea if you knew what you were doing before you attempted something such as this, though.