[en] X-Band and K-Band gyroklystrons are being evaluated for possible application to future linear colliders. So far the authors have examined ten different two- and three-cavity configurations. They have achieved a maximum peak power of 27 MW in ∼ 1 μs pulses at a gain of 37 dB and an efficiency exceeding 32%. The nominal parameters include a 430 kV, 150-200 A beam with an average perpendicular to parallel velocity ratio near one. In this paper, they detail their progress to date and describe their plans for future experiments that should culminate in amplifier outputs in excess of 100 MW