Expanding the Capability Frontier of LLM Agents with ZPD-Guided Data Synthesis - Chen, Xuanzhong; Qiao, Zile; Chen, Guoxin; Su, Liangcai; Zhang, Zhen; Wang, Xinyu; Xie, Pengjun; Huang, Fei; Zhou, Jingren; Jiang, Yong; Chen, Ting (International Conference on Learning Representations, 2026)