[2608.14465] You Only Pass Once: Answering and Abstaining Together in a Single Forward Pass of a Frozen Language Model Skip to main content Search Submit Donate Log in Search arXiv Press Enter to search · Advanced search Computer Science > Computation and Language arXiv:2608.14465 (cs) [Submitted on 14 Aug 2026] Title: You Only Pass Once: Answering and Abstaining Together in a Single Forward Pass of a Frozen Language Model Authors: Ziyang Luo , Zhongyao Chu , Xinjie He , Youting Wang , Xukui Qin , Runxiong Wu , Yan-Syuan Chen View a PDF of the paper titled You Only Pass Once: Answering and Abstaining Together in a Single Forward Pass of a Frozen Language Model, by Ziyang Luo and 6 other authors View PDF HTML (experimental) Abstract: A frozen language model on reasoning tasks has two coupled weaknesses: it under-uses evidence its own residual stream already encodes, and it fails to detect when the input is insufficient to answer, so it confabulates. This paper consolidates two research lines that address these on the same residual stream: a conditional steering probe writes the stream at mid-stack layers and recovers reasoning accuracy from a frozen backbone, and a zero-shot sufficiency direction reads the stream and abstains when information is insufficient. Deployed in one forward pass they interfere: the steering write shifts the state the direction reads, costing up to 8 AUROC points of cross-domain transfer on small models; a separate clean pass doubles inference cost. We keep the direction fixed and train a small network to reconstruct the pre-steering residual from the steered one -- mean-squared error on (steered, clean) pairs, no sufficiency labels -- and read the direction on the reconstruction. The resulting system, YOPO (You Only Pass Once), answers, steers, and abstains in one forward pass of a frozen Qwen2.5 backbone (1.5B/3B/7B). End to end, three-way accuracy more than doubles the frozen baseline (0.375->0.798 on 1.5B alphaNLI) and one pass beats the two-pass reference at every scale (0.798/0.830/0.893 vs 0.753/0.790/0.863) and on ten backbones across six model families. We chart the capacity-transfer frontier quantifying the principle that abstention should not be trained in; a source-side audit catches our own alphaNLI construction leaking a surface artifact, so architectural claims are anchored on native-label replications (SQuAD2, RepLiQA, MuSiQue); and on the standard four-domain suite we contribute, to our knowledge, the first answer-or-abstain benchmark, where our gate tops every in-domain dataset and the label-free direction is the only gate family to survive domain transfer. Comments: 24 pages. Ziyang Luo and Zhongyao Chu contributed equally Subjects: Computation and Language (cs.CL) ; Machine Learning (cs.LG) Cite as: arXiv:2608.14465 [cs.CL] (or arXiv:2608.14465v1 [cs.CL] for this version) https://doi.org/10.48550/arXiv.2608.14465 Focus to learn more arXiv-issued DOI via DataCite Submission history From: Ziyang Luo [ view email ] [v1] Fri, 14 Aug 2026 16:44:35 UTC (111 KB) Full-text links: Access Paper: View a PDF of the paper titled You Only Pass Once: Answering and Abstaining Together in a Single Forward Pass of a Frozen Language Model, by Ziyang Luo and 6 other authors View PDF HTML (experimental) TeX Source view license Current browse context: cs.CL < prev | next > new | recent | 2026-08 Change to browse by: cs cs.LG References & Citations NASA ADS Google Scholar Semantic Scholar export BibTeX citation Loading... BibTeX formatted citation × loading... 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