On the Limits of Model Merging for Multilinguality in Pre-Training

Fuente: arXiv
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Autori principali: Aycock, Seth, Vitiugin, Fedor, Umnov, Aleksandr, Monz, Christof, Sima'an, Khalil
Natura: Preprint
Pubblicazione: 2026
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author Aycock, Seth
Vitiugin, Fedor
Umnov, Aleksandr
Monz, Christof
Sima'an, Khalil
author_facet Aycock, Seth
Vitiugin, Fedor
Umnov, Aleksandr
Monz, Christof
Sima'an, Khalil
contents Endowing models with consistent multilingual performance can be achieved by mixing pre-training data, or post-training approaches such as language-specific model merging. In this work, we test whether merging can be applied to monolingually pre-trained models. We conduct a controlled study on the efficacy of mixed, merged, and monolingual pre-training setups. We find that while monolingual pre-training results in strong in-language performance, merging any combination of monolingual models leads to performance collapse due to interference. Our analysis suggests representational similarity is a prerequisite for model merging. We therefore conclude that the flexibility of merging in fine-tuning does not extend trivially to language-specific pre-training.
format Preprint
id arxiv_https___arxiv_org_abs_2605_25846
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle On the Limits of Model Merging for Multilinguality in Pre-Training
Aycock, Seth
Vitiugin, Fedor
Umnov, Aleksandr
Monz, Christof
Sima'an, Khalil
Computation and Language
Endowing models with consistent multilingual performance can be achieved by mixing pre-training data, or post-training approaches such as language-specific model merging. In this work, we test whether merging can be applied to monolingually pre-trained models. We conduct a controlled study on the efficacy of mixed, merged, and monolingual pre-training setups. We find that while monolingual pre-training results in strong in-language performance, merging any combination of monolingual models leads to performance collapse due to interference. Our analysis suggests representational similarity is a prerequisite for model merging. We therefore conclude that the flexibility of merging in fine-tuning does not extend trivially to language-specific pre-training.
title On the Limits of Model Merging for Multilinguality in Pre-Training
topic Computation and Language
url https://arxiv.org/abs/2605.25846