Open climb should be a speed based pitch mode with auto thrust commanding climb thrust, not the autothrust commanding speed
Off course it is but the way it is initiated is through VS, speed in the background. The pitch up occurs to give you a pre set VS and thrust comes up to maintain speed till 95% N1 and then continues to THR CLB and speed maintanence is switched to pitch. Had it not been so and thrust would have moved to climb then to control speed the pitch up may have been too harsh. It's Airbus design I don't how Boeing does it.