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Will it Merge? On The Causes of Model Mergeability

Published: January 10, 2026 | arXiv ID: 2601.06672v1

By: Adir Rahamim , Asaf Yehudai , Boaz Carmeli and more

Potential Business Impact:

Makes AI models combine better by using what they already know.

Business Areas:
Machine Learning Artificial Intelligence, Data and Analytics, Software

Model merging has emerged as a promising technique for combining multiple fine-tuned models into a single multitask model without retraining. However, the factors that determine whether merging will succeed or fail remain poorly understood. In this work, we investigate why specific models are merged better than others. To do so, we propose a concrete, measurable definition of mergeability. We investigate several potential causes for high or low mergeability, highlighting the base model knowledge as a dominant factor: Models fine-tuned on instances that the base model knows better are more mergeable than models fine-tuned on instances that the base model struggles with. Based on our mergeability definition, we explore a simple weighted merging technique that better preserves weak knowledge in the base model.

Country of Origin
🇮🇱 Israel

Page Count
20 pages

Category
Computer Science:
Computation and Language