Released June 2016, identified by model number A3003 in Europe, A3000 in China and North America (according to https://forums.oneplus.net/threads/oneplus-3-regions-model-numbers.452381/)
The front camera was changed, and the battery is a little bigger.
The USB -port seams to be the same as the speaker.
I would say that apart from the logic board and the changed parts like the camera or the battery, other parts might be replaceable from 3 to 3T or wise versa.