It seems like OnePlus is looking forward in introducing the ‘Face Unlock’ feature across all of its models. With the arrival of OxygenOS 5.0 update, the OnePlus 3 and 3T too have got access to the feature, which was introduced by the company through the recently launched model, OnePlus 5T. That said, with the company not making any official statements, it has to be noted that one should change the custom settings, once s/he migrated the device to OxygenOS 5.0 update.
Interestingly, the ‘Face Unlock’ feature in these devices doesn’t work on conditions, when the screen is turned off.