@inproceedings{zhang-etal-2025-iopo,
    title = "{IOPO}: Empowering {LLM}s with Complex Instruction Following via Input-Output Preference Optimization",
    author = "Zhang, Xinghua  and
      Yu, Haiyang  and
      Fu, Cheng  and
      Huang, Fei  and
      Li, Yongbin",
    editor = "Che, Wanxiang  and
      Nabende, Joyce  and
      Shutova, Ekaterina  and
      Pilehvar, Mohammad Taher",
    booktitle = "Proceedings of the 63rd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)",
    month = jul,
    year = "2025",
    address = "Vienna, Austria",
    publisher = "Association for Computational Linguistics",
    url = "https://preview.aclanthology.org/ingestion-acl-25/2025.acl-long.1079/",
    pages = "22185--22200",
    ISBN = "979-8-89176-251-0",
    abstract = "In the realm of large language models (LLMs), the ability of models to accurately follow instructions is paramount as more agents and applications leverage LLMs for construction, where the complexity of instructions are rapidly increasing. However, on the one hand, there is only a certain amount of complex instruction evaluation data; on the other hand, there are no dedicated algorithms to improve the ability to follow complex instructions. To this end, this paper introduces Trace, a benchmark for improving and evaluating the complex instruction-following ability, which consists of 120K training data and 1K evaluation data. Furthermore, we propose IOPO (Input-Output Preference Optimization) alignment method which takes both input and output preference pairs into consideration, where LLMs not only rapidly align with response preferences but also meticulously explore the instruction preferences. Extensive experiments on both in-domain and out-of-domain datasets confirm the effectiveness of IOPO, showing 8.15{\%}, 2.18{\%} improvements on in-domain data and 5.91{\%}, 2.83{\%} on out-of-domain data compared to SFT and DPO respectively. Our code and dataset are released at https://anonymous.4open.science/r/Code7-34A5."
}