AC4.04 adds GPS yaw support, thanks @, we tested this, and it works great.
hardware:
C-RTK 9P
CUAV nora flight control
CUAV xunwing X4
Air link (CUAV 4g data transmission)
Firmware: AC4.04 official version.
Here is the test video:
https://www.youtube.com/watch?v=Kh_6TynYqEI&t=3s
Configuration:
https://ardupilot.org/copter/docs/common-gps-for-yaw.html