LoRA Soups: Merging LoRAs for Practical Skill Composition Tasks

Akshara Prabhakar, Yuanzhi Li, Karthik Narasimhan, Sham Kakade, Eran Malach, Samy Jelassi


Abstract
Low-Rank Adaptation (LoRA) is a popular technique for parameter-efficient fine-tuning of Large Language Models (LLMs). We study how different LoRA modules can be merged to achieve skill composition—testing the performance of the merged model on a target task that involves combining multiple skills, each skill coming from a single LoRA. This setup is favorable when it is difficult to obtain training data for the target task and when it can be decomposed into multiple skills. First, we identify practically occurring use-cases that can be studied under the realm of skill composition, e.g. solving hard math-word problems with code, creating a bot to answer questions on proprietary manuals or about domain-specialized corpora. Our main contribution is to show that concatenation of LoRAs (CAT), which optimally weights LoRAs that were individually trained on different skills, outperforms existing model- and data- merging techniques; for instance on math-word problems, CAT beats these methods by an average of 43% and 12% respectively. Thus, this paper advocates model merging as an efficient way to solve compositional tasks and underscores CAT as a simple, compute-friendly and effective procedure.
Anthology ID:
2025.coling-industry.55
Volume:
Proceedings of the 31st International Conference on Computational Linguistics: Industry Track
Month:
January
Year:
2025
Address:
Abu Dhabi, UAE
Editors:
Owen Rambow, Leo Wanner, Marianna Apidianaki, Hend Al-Khalifa, Barbara Di Eugenio, Steven Schockaert, Kareem Darwish, Apoorv Agarwal
Venue:
COLING
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
644–655
Language:
URL:
https://aclanthology.org/2025.coling-industry.55/
DOI:
Bibkey:
Cite (ACL):
Akshara Prabhakar, Yuanzhi Li, Karthik Narasimhan, Sham Kakade, Eran Malach, and Samy Jelassi. 2025. LoRA Soups: Merging LoRAs for Practical Skill Composition Tasks. In Proceedings of the 31st International Conference on Computational Linguistics: Industry Track, pages 644–655, Abu Dhabi, UAE. Association for Computational Linguistics.
Cite (Informal):
LoRA Soups: Merging LoRAs for Practical Skill Composition Tasks (Prabhakar et al., COLING 2025)
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PDF:
https://aclanthology.org/2025.coling-industry.55.pdf