OnePlus has now started rolling out Oxygen OS 4.0.1 update for the OnePlus 3/3T smartphones shortly after the company rolled out OxygenOS 4.0 Nougat based update on December 31st. Read More: Install Official Android 7.0 Nougat on OnePlus 3/3T
This incremental update fixes a few bugs for those who had already updated to 4.0, for the rest it adds Android 7.0 Nougat with new notifications design, new settings menu, multi-window support, direct reply in notifications, improved shelf and more.
With the 4.0.1 OxygenOS update, OnePlus has also fixed proximity sensor issues during calls, updated APN settings for some carriers and then there's better system stability as well.
There are still some bugs and known issues that OnePlus has listed on their forum here, which you can have a look at and decide to update or nor