VASTU: Language Models Struggle to Recognize Online Community Values

Agam Goyal, Xianyang Zhan, Charlotte Lambert, Koustuv Saha, Eshwar Chandrasekharan


Abstract
Online communities develop distinct norms for content they collectively value, yet it remains unclear whether current language models can recognize locally valued contributions in context. We formalize this as community-conditioned preference prediction and introduce Vastu (Value-Aware Social Tuning), a benchmark of 75,000 Reddit comments from 15 communities spanning Gaming, Science, Q&A, Advice, and Politics. We evaluate four model families—prompted LLMs, LoRA-adapted SLMs, supervised encoders, and feature-based classifiers—across global, local, and context-conditioned settings. Our central finding is that parametric adaptation consistently outperforms prompting: supervised encoders reach 0.74 AUROC and fine-tuned SLMs 0.64–0.71, while the best prompted result is only 0.62. This gap is not merely quantitative—vanilla prompting yields over 80% false-negative rates, systematically discarding content communities actually value. Conversational context narrows but does not close this divide. Together, these results suggest that local preference recognition requires community-specific training signal, not just better prompting. Our work supports future research on community-aware reward modeling, feed curation, and positive moderation.
Anthology ID:
2026.emnlp-main.231
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:
5311–5327
Language:
URL:
https://aclanthology.org/2026.emnlp-main.231/
DOI:
Bibkey:
Cite (ACL):
Agam Goyal, Xianyang Zhan, Charlotte Lambert, Koustuv Saha, and Eshwar Chandrasekharan. 2026. VASTU: Language Models Struggle to Recognize Online Community Values. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 5311–5327, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
VASTU: Language Models Struggle to Recognize Online Community Values (Goyal et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.231.pdf