Tokenization Risk as a Control Signal for Adaptive RAG

Norbert Braunschweiler, Rama Doddipatla, Nigel Collier


Abstract
Retrieval-Augmented Generation (RAG) systems can degrade on inputs containing specialized, low-frequency vocabulary, where subword tokenization introduces fragmentation that disrupts both retrieval and generation. We introduce tokenization risk, a lightweight metric that predicts these failures. We show that (i) tokenization risk strongly correlates with degradation in retrieval and answer quality, and (ii) static mitigations (e.g., hybrid retrieval) provide only partial gains. To address this, we propose risk-based routing, which adaptively switches retrieval and generation strategies based on risk. Experiments on SpecialVocabBench, a risk-stratified benchmark of technical documents, demonstrate that this approach consistently improves retrieval accuracy and answer correctness with small system changes, establishing tokenization risk as an effective control signal for adaptive RAG.
Anthology ID:
2026.uncertainlp-main.2
Volume:
The Proceedings of the Third Workshop on Uncertainty-Aware NLP
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Wilker Aziz, Jonathan Berant, Bryan Eikema, Evgenia Ilia, Marie-Catherine de Marneffe, Barbara Plank, Artem Shelmanov, Swabha Swayamdipta, Jörg Tiedemann, Artem Vazhentsev, Raúl Vázquez, Chrysoula Zerva
Venues:
UncertaiNLP | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
19–29
Language:
URL:
https://aclanthology.org/2026.uncertainlp-main.2/
DOI:
Bibkey:
Cite (ACL):
Norbert Braunschweiler, Rama Doddipatla, and Nigel Collier. 2026. Tokenization Risk as a Control Signal for Adaptive RAG. In The Proceedings of the Third Workshop on Uncertainty-Aware NLP, pages 19–29, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Tokenization Risk as a Control Signal for Adaptive RAG (Braunschweiler et al., UncertaiNLP 2026)
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PDF:
https://aclanthology.org/2026.uncertainlp-main.2.pdf