@inproceedings{uddin-bauer-2026-conformal,
    title = "Conformal {LLM} Routing with Distribution-Free Safety Guarantees",
    author = "Uddin, Iqtedar  and
      Bauer, Andr{\'e}",
    editor = "T.Y.S.S., Santosh  and
      Rodriguez, Juan Diego  and
      de Gibert, Ona",
    booktitle = "Proceedings of the 64th Annual Meeting of the {A}ssociation for {C}omputational {L}inguistics ({ACL} 2026)",
    month = jul,
    year = "2026",
    address = "San Diego, California, United States",
    publisher = "Association for Computational Linguistics",
    url = "https://preview.aclanthology.org/ingest-acl/2026.acl-srw.70/",
    pages = "791--799",
    ISBN = "979-8-89176-393-7",
    abstract = "LLM routing directs queries to a cheaper model when it suffices and to an expensive model otherwise, reducing inference cost. Existing input-based routers optimize cost-performance trade-offs but provide no formal bound on how often the cheaper model fails among routed queries. We adapt a proactive conformal gate framework to LLM routing. A logistic regression gate trained on text embeddings predicts per-query safety, and Clopper-Pearson conformal calibration selects a routing threshold that guarantees the violation rate among routed queries stays below $\alpha$ (the violation tolerance) with probability at least $1 - \delta$ (the confidence level). On two benchmarks covering math reasoning (GSM8K) and multi-domain knowledge (MMLU), routing between Mixtral-8x7B and GPT-4 (a 24.5$\times$ cost difference), our method maintains the target $\alpha$ within the $\delta$ tolerance across a sweep from 0.05 to 0.50, while a validation-tuned baseline crosses the violation boundary on GSM8K. A feasibility analysis across all 10 RouterBench models reveals that routability is jointly model- and task-dependent. To our knowledge, this is the first input-based LLM router with distribution-free safety guarantees."
}