Well this is a bit of a surprise. When Sprint launched its carrier-branded version of the LG G Stylo back in June of this year, it didn't garner too much attention - it's just another big-screen, low-price device filling out the mid range, albeit with a somewhat novel built-in stylus. If you were to make a list of the phones you'd expect to see rocking the latest version of Android by the end of 2015, the G Stylo might be just in front of the Kyocera Echo.
But here we are, only a few days before New Year's, and Sprint has officially announced an Android 6.0 update for the phone. According to this Sprint support article, a Marshmallow OTA should be zipping across the airwaves to G Stylo owners as soon as today (though it will probably be a week or more before the rollout reaches all eligible customers). This is the third OTA update for this particular model - it got Android 5.1 back in June - but aside from the Android software bump, there's no mention of software tweaks or new features.
Sprint's version of the G Stylo and a model specifically for its subsidiary MVNO Boost Mobile launched at around the same time earlier this year, but so far there's no mention of an upgrade for phones on the budget-focused network. T-Mobile also carries the G Stylo, so we can hope that LG will send them the update soon as well.