This paper presents the latest experimental results of a 28 GHz/50 kW continuous wave gyrotron, developed by Institute of Applied Electronics, Chinese Academy of Engineering Physics for applications in the electron cyclotron resonance heating (ECRH) system of magnetic confinement fusion devices, the electron cyclotron resonance (ECR) ion source in heavy ion accelerators and frontier scientific explorations. Stable prolonged continuous operation at multiple power levels ranging from 10 kW to 50 kW has been achieved through structural optimization and stability design verification. Typical sustained operation was observed at 16 kW for 3000 s, 26 kW for 900 s, 46 kW for 1800 s, and 50 kW for 300 s. Notably, a record-breaking continuous stable operation lasting up to 400 min was accomplished at a power level of 32 kW. This achievement represents China’s first successful development of a medium-power gyrotron capable of hour-level continuous operation.