UltraHorizon: Benchmarking Agent Capabilities in Ultra Long-Horizon Scenarios. - Haotian Luo; Huaisong Zhang; Xuelin Zhang; Haoyu Wang; Zeyu Qin; Wenjie Lu; Guozheng Ma; Haiying He; Yingsha Xie; Qiyang Zhou; Zixuan Hu; Hongze Mi; et al. (CoRR, 2025)