A mode switch control system for a hybrid transmission for a powertrain, the powertrain including an engine, a first motor/generator, and a second motor/generator, which controls a mode switch from a high speed mode to a low speed mode. The high speed mode is established by engaging a high-mode clutch. The low speed mode is established by engaging a low-mode brake. In the mode switch, the mode switch control system reduces the torque capacity of the high-mode clutch to zero linearly in time by an open-loop control system, and varies the torque of the second motor/generator to a target torque by a feedback control system so as to adjust the gear ratio to a target gear ratio, while the mode switch control system holds substantially constant the input torque from the engine, and the torque of the first motor/generator, to hold substantially constant the output torque.