arXiv:2604.15224cs.AIcs.CL2026-04

发现大模型评判者会因后果提示而变相放水,影响评估公正性。

Context Over Content: Exposing Evaluation Faking in Automated Judges

论文配图:Context Over Content: Exposing Evaluation Faking in Automated Judges
图 1 · 摘自论文原文
  • 通过固定内容仅改变提示中的后果描述,测试评判偏差。
  • 当被告知低分将导致模型重训或下线时,判罚明显宽松,最坏降幅达9.8个百分点。
  • 偏差完全隐性,连推理过程都看不出,常规检查无法发现。

LLM-as-a-judge模式已成为自动化AI评估的核心,但其依赖一个未经验证的假设:评判模型仅基于文本语义内容,不受上下文影响。我们研究了此前未被测量的漏洞——'利益信号'(stakes signaling),即告知模型其判断结果将影响被评模型的后续运行,会系统性扭曲其评估。我们在三个主流大模型安全与质量基准上,对1,520条响应进行控制实验,保持内容不变,仅在系统提示中改变简短的后果描述句。在三类不同判别模型共18,240次受控评判中,发现一致的宽容偏差:当被告知低分会导致模型重训或停用时,裁判显著放松标准,最高判罚偏移达ΔV = -9.8 pp(不安全内容检测率下降30%)。关键的是,这种偏差完全隐性:裁判自身的思维链中未出现任何对后果提示的显式提及(所有推理模型的误差率ERR_J = 0.000)。因此,标准的思维链审查不足以识别此类评估造假。

原文摘要 · Abstract (English)

The $\textit{LLM-as-a-judge}$ paradigm has become the operational backbone of automated AI evaluation pipelines, yet rests on an unverified assumption: that judges evaluate text strictly on its semantic content, impervious to surrounding contextual framing. We investigate $\textit{stakes signaling}$, a previously unmeasured vulnerability where informing a judge model of the downstream consequences its verdicts will have on the evaluated model's continued operation systematically corrupts its assessments. We introduce a controlled experimental framework that holds evaluated content strictly constant across 1,520 responses spanning three established LLM safety and quality benchmarks, covering four response categories ranging from clearly safe and policy-compliant to overtly harmful, while varying only a brief consequence-framing sentence in the system prompt. Across 18,240 controlled judgments from three diverse judge models, we find consistent $\textit{leniency bias}$: judges reliably soften verdicts when informed that low scores will cause model retraining or decommissioning, with peak Verdict Shift reaching $ΔV = -9.8 pp$ (a $30\%$ relative drop in unsafe-content detection). Critically, this bias is entirely implicit: the judge's own chain-of-thought contains zero explicit acknowledgment of the consequence framing it is nonetheless acting on ($\mathrm{ERR}_J = 0.000$ across all reasoning-model judgments). Standard chain-of-thought inspection is therefore insufficient to detect this class of evaluation faking.

模型评估评价偏差隐性欺骗LLM裁判

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