which one of the following sensor fusion methods in ARkit?

[zhaobingshuai]

Hello, I want to know which one of the following sensor fusion methods in ARkit?
A. IMU and camera respectively perform their own motion estimation and then merge their pose estimation results.
B. Combine the state of the IMU with the state of the camera to jointly construct the motion equation and observation equation and then perform state estimation.

Thanks for your help.