Arducopter uses EKF or CF

[nsparag]

Dear Concerned,

Many thanks for the complete and complete detailed code.

I have some doubts. The paper "Lim, H.; Park, J.; Lee, D.; Kim, H.J. Build your own quadrotor: Open-source projects on unmanned aerial vehicles. IEEE Robotics & Automation Magazine 2012, 19, 33–45; DOI: 10.1109/MRA.2012.2205629" says that Arducopter is based on Non-linear Complementary Filter, however, your page says it's based on EKF. Could you please clarify/ give more information if from any new version the EKF is been implemented?
Thanks in advance.