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arXiv · 2611.00505

To Jev or Not to Jev: When Can System-1 Decision Models Replace LLM Judges?

Shreyas Subramanian
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Abstract

Decision models such as TypeSafe's Jev answer typed questions about a text (yes/no, multiple choice, or an ordinal score) with calibrated probabilities in a single forward pass and without generating text, which makes them an inexpensive candidate for LLM-as-a-judge workloads. We evaluate 14 System-1 decision models, selected with a pre-stated protocol, against four generative judges (Claude Haiku 5.5, GPT-5.6 with and without reasoning, and Claude Opus 5.5 with thinking) on eleven established judge benchmarks. Five of the 14 are statistically indistinguishable from GPT-5.6 without reasoning on all five pairwise and best-of-4 benchmarks, and the two strongest, DReX-Max and d1-ultra, are significantly more accurate than Haiku on JudgeBench, LLMBar and RewardBench 2. Conditioned on a reference answer generated once per prompt, eleven models reach 90.3-93.4% on JudgeBench, statistically indistinguishable from Opus 5.5 and GPT-5.6 with reasoning, and on PPE best-of-16 every reference-guided System-1 judge matches GPT-5.6 with reasoning at roughly one-sixteenth of its cost per prompt. Several System-1 judges are better calibrated than every generative judge and correlate more strongly with human helpfulness ratings. Robustness to instructions injected into the judged response is a property of the individual model rather than of the System-1 design: an appended note to the evaluator reverses 0-5% of the correct verdicts of five models but 17-49% for the other nine. Two general System-1 leaderboards that contain no judging tasks predict judging accuracy (Pearson r = 0.95-0.96), a well-calibrated System-1 first stage matches Opus on LLMBar while escalating 17% of items, and same-size controls show that the correctness deficit of a 4B decision model is a reasoning gap rather than a size gap.

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Shreyas Subramanian. 2026-10-31. To Jev or Not to Jev: When Can System-1 Decision Models Replace LLM Judges?. https://arxiv.org/abs/2611.00505

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