这篇论文发现大多数大模型判断概率时普遍乐观，只有Anthropic的模型偏悲观，还揭示对齐训练会改变偏差方向，值得AI开发者和伦理研究者关注。
为了检测语言模型在概率判断中的方向性偏差，研究者提出OptimismBench，使用反向配对法计算符号偏差分数。对8个提供商的16个模型测试发现，14个模型呈现乐观偏差，仅Anthropic的旗舰层表现悲观。11组基座模型与聊天模型对比显示，后训练方向在不同模型家族中产生相反偏差。在17个模型、6种语言的比较中，模型身份主导语言因素，模型间方差是语言间方差的4.7倍。研究者发布了3870个条目、覆盖10种语言的偏差审计数据集。
OptimismBench: Forecasting Bias and the Alignment Effect in Language Model Judgment
Large language models are increasingly used as decision aids whose probability judgments shape downstream choices. Whether those judgments carry a systematic directional tilt has been hard to detect: calibration metrics aggregate unsigned errors, and naturalistic uncertainty offers no ground-truth probability. When an LLM rates a startup's success at 70% but its failure at 15%, the missing 15 points expose a distortion no aggregate score flags. We introduce OptimismBench, which detects directional bias with inverted pairs: each scenario elicits both P(success) and P(failure), and asymmetry between the two framings yields a signed bias score without ground truth. Across 16 models from 8 providers, fourteen are optimistic; pessimism appears only in Anthropic's frontier tier. Eleven matched base-versus-chat pairs across four families show post-training sets the sign of the bias, with opposite shifts in different families. The pattern survives prompt, temperature, perspective, and self-debiasing ablations. A seventeen-model six-language comparison further shows model identity dominates language, with inter-model variance at 4.7x inter-language variance. We release 3,870 items across 10 languages for per-model directional-bias auditing. When alignment makes a model more helpful, it also tilts its probabilities; downstream pipelines inherit the tilt by default.