The Joetsu Thermal Power Station Unit No. 1 of Tohoku Electric Power Co., Inc., which started operation in December 2022, employs a 1,650°C class JAC gas turbine from Mitsubishi Heavy Industries, Ltd. (MHI) and has achieved the world's highest plant thermal efficiency of 63.62%. Even with regard to the operability, which generally has a trade-off relationship with the thermal efficiency, this plant attained about 25% shorter start-up time and about 3 times higher power output change rate (ramp rate) compared to conventional gas turbine combined cycle plants, and has a minimum output as low as 25% of the rated output. Thus, it is also expected to promote the introduction and expansion of renewable energy sources with large fluctuations. This report describes the features of the plant, which we believe will contribute to the development of the electric power industry toward further environmental load reduction and carbon neutrality due to its high efficiency and high operability.