This year Apple stopped including a Lighting to 3.5mm adapter with its iPhones (even the old models). Will OnePlus follow suit now that its upcoming phone doesn't have a 3.5mm jack? We don't know for sure, but a leaked price list gives us a glimpse of the OnePlus 6T accessories. A USB-C to 3.5mm adapter cable will cost 8.95 in Europe. Apple sells its adapter for 10.00 so about the same. However, OnePlus doesn't have the practice of including headphones in its retail box, so our guess is that the adapter will not be included either. The new Bullets V2 headphones with USB-C plug...
Source: https://www.gsmarena.com/prices_of_oneplus_6t_accessories_leak-news-33531.php