RCEM: Robust Conversational Search EMbedder in Distributional Shift

Kilho Son, Bo-June Paul Hsu, Cha Zhang, Dinei Florencio


Abstract
We propose RCEM, a Robust Conversational search EMbedder that augments text embedders with LLM query reformulation capabilities while approximately preserving their original generalization performance. Unlike prior conversational dense retrieval approaches that learn direct conversation-to-passage matching, RCEM aligns conversations, prepended by special token, to LLM-rewritten queries, while attempting to preserve the original embedding space. The approximately preserved embedding space automatically maps the rewritten queries to the relevant passages. As a result, RCEM (1) reduces overfitting by aligning conversations to shorter rewritten queries rather than full passages, (2) eliminates the need for conversation-to-passage relevance labels for training, and (3) approximately preserves the original embedding space, enabling conversational retrieval over indexes built by the base embedder without re-indexing. Extensive experiments show that RCEM consistently outperforms prior approaches, improving up to 30% retrieval accuracy under distributional shift.
Anthology ID:
2026.emnlp-industry.167
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing: Industry Track
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Pepa Atanasova, Gholamreza Haffari, Minghan Wang
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
2830–2843
Language:
URL:
https://aclanthology.org/2026.emnlp-industry.167/
DOI:
Bibkey:
Cite (ACL):
Kilho Son, Bo-June Paul Hsu, Cha Zhang, and Dinei Florencio. 2026. RCEM: Robust Conversational Search EMbedder in Distributional Shift. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing: Industry Track, pages 2830–2843, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
RCEM: Robust Conversational Search EMbedder in Distributional Shift (Son et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-industry.167.pdf