In an announcement the company said: "After internal discussions and evaluation, we have decided to focus our development resources on the Android P project, instead of upgrading the OnePlus 3 and 3T device to Android 8.1."
So while 3 and 3T owners will miss out on a potential Android 8.1 update in the next few months, the longer term is looking for rosy.
Gotta get in line
OnePlus has been working alongside Google to deliver the Android P Beta to its OnePlus 6 device, and it's understandable that it would rather focus all its attention on the upcoming version of Android.
However, there may be a bit of a wait for Android P to arrive on the 3 and 3T, as OnePlus goes on to say "the Android P update will be available on the OnePlus 6, OnePlus 5/T and OnePlus 3/3T, in this order."
In the past OnePlus has been relatively efficient in getting out software updates, but we expect the Android P update to land on the 3 and 3T either at the end of this year, or early into 2019.