Stateful Visual Encoders for Vision-Language Models

Zirui Wang, Junwei Yu, Adam Yala, David M. Chan, Joseph E. Gonzalez, Trevor Darrell


Abstract
Vision-language models (VLMs) are increasingly used in multi-image, multi-turn agentic settings where decisions depend on visual changes. However, in existing open-weight VLMs, visual comparisons happen only inside the language model, while the visual encoder itself remains stateless: each image is encoded independently, without access to the prior visual context. As a result, small but task-critical changes may be attenuated before the language model has a chance to compare them, especially when those changes do not affect the high-level semantics of the scene. We introduce a Stateful Visual Encoder, which conditions each visual representation on prior visual features. Under supervised finetuning, VLMs equipped with stateful encoders achieve consistent improvements on controlled tasks involving cross-image spatial aggregation, multi-object visual differencing, and visual trajectory behavior cloning. These improvements are consistent across input resolutions, language model sizes, and VLM backbones. Finally, we validate our model on real-world tasks, including longitudinal radiology, fine-grained image comparison, and remote sensing, where stateful encoders consistently improve generalist VLM baselines and can match or surpass specialized models in selected domains.
Anthology ID:
2026.emnlp-main.707
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
16377–16399
Language:
URL:
https://aclanthology.org/2026.emnlp-main.707/
DOI:
Bibkey:
Cite (ACL):
Zirui Wang, Junwei Yu, Adam Yala, David M. Chan, Joseph E. Gonzalez, and Trevor Darrell. 2026. Stateful Visual Encoders for Vision-Language Models. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 16377–16399, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Stateful Visual Encoders for Vision-Language Models (Wang et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.707.pdf