While large language models (LLMs) fine-tuned with lightweight adapters achieve strong performance across diverse tasks, their performance on individual tasks depends on the fine-tuning strategy. Fusing independently trained models with different strengths has shown promise for multi-task learning through three main strategies: ensembling, which combines outputs from independent models; merging, which fuses model weights via parameter averaging; and routing, which integrates models in an input-dependent fashion. However, many design decisions in these approaches remain understudied, and the relative benefits of more sophisticated ensembling, merging and routing techniques are not fully understood. We empirically evaluate their trade-offs, addressing two key questions: What are the advantages of going beyond uniform ensembling or merging? And does the flexibility of routing justify its complexity? Our findings indicate that non-uniform ensembling and merging improve performance, but routing offers even greater gains. To mitigate the computational cost of routing, we analyze expert selection techniques, showing that clustering and greedy subset selection can maintain reasonable performance with minimal overhead. These insights advance our understanding of model fusion for multi-task learning.
Multi-Study Boosting: Theoretical Considerations for Merging vs. Ensembling
Harvard T.H. Chan School of Public Health(哈佛陈曾熙公共卫生学院);Dana-Farber Cancer Institute(达纳-法伯癌症研究所);Harvard University(哈佛大学);Boston University School of Public Health(波士顿大学公共卫生学院)
Merging versus Ensembling in Multi-Study Prediction: Theoretical Insight from Random Effects
Massachusetts General Hospital(麻省总医院);Dana Farber Cancer Institute(丹娜法伯癌症研究院);Harvard T.H. Chan School of Public Health(哈佛陈曾熙公共卫生学院);Boston University School of Public Health(波士顿大学公共卫生学院)
Merging Multi-Task Models via Weight-Ensembling Mixture of Experts
National Engineering Research Center for Multimedia Software(国家多媒体软件工程技术研究中心);School of Computer Science, Wuhan University(武汉大学计算机学院);Hubei Luojia Laboratory(湖北珞珈实验室);Sun Yat-sen University(中山大学);JD Explore Academy(京东探索研究院);Mohamed bin Zayed University of Artificial Intelligence(穆罕默德·本·扎耶德人工智能大学);Nanyang Technological University(南洋理工大学)
A Unified Generalization Framework for Model Merging: Trade-offs, Non-Linearity, and Scaling Laws
National University of Defense Technology(国防科技大学);Wuhan University(武汉大学);School of Cyber Science and Technology, Shenzhen Campus of Sun Yat-sen University(中山大学信息科学与技术学院深圳校区);Hebei University of Technology(河北工业大学)
MAP: Low-compute Model Merging with Amortized Pareto Fronts via Quadratic Approximation
University of Pennsylvania(宾夕法尼亚大学);MILA(蒙特利尔人工智能研究院);ServiceNow(ServiceNow公司);Amazon AGI(亚马逊人工智能实验室);Université de Montréal(蒙特利尔大学);HKUST(香港科技大学);University of Florida(佛罗里达大学)
Towards Efficient Pareto Set Approximation via Mixture of Experts Based Model Fusion
School of Computer Science, Wuhan University(武汉大学计算机学院);School of Computer Science and Engineering, Sun Yat-sen University(中山大学计算机科学与工程学院);University of Oxford(牛津大学);School of Computer Science, Beijing Institute of Technology(北京理工大学计算机学院);Nanyang Technological University(南洋理工大学)