Although OnePlus has prided itself on having an open channel of communication with its supporters, there have been instances in the past where it clearly decides on what it sees and what it doesn't.
Perhaps the most famous of these instances is the group of users who that purchased the OnePlus 2 and were promised an update to Android 7.0 Nougat. After a year of avoiding the topic, the firm finally came out and admitted that it wouldn't be providing the update.
Luckily, the company is being a bit more clear when it comes to its OnePlus 3 and OnePlus 3T as it has stated in a forum post that Android O will be the last OS update the handsets receive. While this might be the case, the firm did state that they would be delivering security updates "for the foreseeable future, and offer support for individual application updates". Hopefully, Project Treble should help streamline the Android O update experience for both OnePlus and handset owners.
For those looking for OS updates beyond Android O, you'll most likely have to turn to a custom OS from the likes of Lineage.