Quaternium, a European company that designs and develops multi rotor drones, claims to have set the world record of endurance with a flight of 4 hours and 40 minutes with its HYBRiX.20 fuel-electric quadcopter. In a release they state that “this flight time beats any former demonstration ever made with an electric, hybrid of hydrogen multicopter.” This flight would be 4 minutes longer than one made by Skyfront.
You can view their video demonstrating the flight time here. From the video it appears the drone simply hovered for the time that it was in the air.
The HYBRiX.20 RPA was designed in 2014 and the first model was built in 2015. The drone incorporated a hybrid technology to power drones. This technology overcomes the primary limitation of multi rotor drones which is limited flight time. HYBRiX.20 is a fuel-electric aircraft, which means that it is an electric multirotor with a powerful genset based on a 2-stroke engine that keeps the battery charged during flight.