Routing-Based Continual Learning for Multimodal Large Language Models

Jay Mohta, Kenan E. Ak, Gwang Gook Lee, Dimitrios Dimitriadis, Yan Xu, Mingwei Shen


Abstract
Multimodal Large Language Models (MLLMs) struggle with continual learning, often suffering from catastrophic forgetting when adapting to sequential tasks. We introduce a routing-based architecture that integrates new capabilities while robustly preserving foundational knowledge. While Multi-Task Learning (MTL) is a strong performance reference, its training cost grows linearly with the number of tasks. In contrast, our method maintains fixed per-task training data and compute requirements regardless of the task sequence length. Across models ranging from 2B to 8B parameters, we demonstrate that our routing approach performs on par with MTL while retaining the training efficiency of sequential fine-tuning. Beyond merely mitigating forgetting, we observe that token-level routing facilitates cross-modal transfer, leveraging knowledge from one modality to bolster performance in another. We also show that routing remains robust even with large expert pools and effectively capitalizes on task relatedness. Finally, we show that our method scales favorably, with larger models exhibiting minimal degradation compared to fully specialized fine-tuning.
Anthology ID:
2026.aacl-long.99
Volume:
Proceedings of the 15th International Joint Conference on Natural Language Processing and the 5th Conference of the Asia-Pacific Chapter of the Association for Computational Linguistics (Volume 1: Long Papers)
Month:
November
Year:
2026
Address:
Hengqin, China
Editors:
Yue Zhang, Ruifeng Xu, Ayu Purwarianti, Tong Rong, Jun Suzuki
Venues:
AACL | IJCNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
2177–2192
Language:
URL:
https://aclanthology.org/2026.aacl-long.99/
DOI:
Bibkey:
Cite (ACL):
Jay Mohta, Kenan E. Ak, Gwang Gook Lee, Dimitrios Dimitriadis, Yan Xu, and Mingwei Shen. 2026. Routing-Based Continual Learning for Multimodal Large Language Models. In Proceedings of the 15th International Joint Conference on Natural Language Processing and the 5th Conference of the Asia-Pacific Chapter of the Association for Computational Linguistics (Volume 1: Long Papers), pages 2177–2192, Hengqin, China. Association for Computational Linguistics.
Cite (Informal):
Routing-Based Continual Learning for Multimodal Large Language Models (Mohta et al., AACL-IJCNLP 2026)
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PDF:
https://aclanthology.org/2026.aacl-long.99.pdf