Although Google has already started testing Android N with developers, Android handset makers are still busy updating their wares to Marshmallow. Case in point: LG, and its G3. The flagship smartphone from 2014 is now receiving the update to Android 6.0 Marshmallow both on AT&T and T-Mobile, according to multiple reports from owners.
T-Mobile's model isn't currently enjoying an over-the-air rollout of the update, so to download and install it you'll need to use LG's desktop software. Even so, the new release may not yet show as being available for everyone.
If you bought your G3 from AT&T, then you can check for the update by going to the phone's settings and hopefully grab it over-the-air. If you do succeed in updating, you'll then be on software version D85030k, as you can see from the screenshots above.
The update also includes the March security patches, but unfortunately not this month's. Another interesting tidbit is that this is Android 6.0, and not Android 6.0.1 - even though that iteration has been out since last November. Hopefully LG will issue another Marshmallow update for the G3 in the future, bringing it up to date.