GEPO: Group Expectation Policy Optimization for Stable Heterogeneous Reinforcement Learning - Zhang, Han; Zheng, Ruibin; YI, ZEXUAN; Zhang, Zhuo; Peng, Hanyang; WANG, HUI; Qi, Jiayin; Fang, Binxing; Xu, Ruifeng; Yu, Yue (International Conference on Learning Representations, 2026)