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arXiv Machine Learning · 2026/7/30 17:38:23

Sample More, Reflect Less: Self-Refine and Reflexion Lose to Repeated Sampling at Equal Token Cost, from 1.5B to 7B

AI 中文解读
新研究给AI“自省”泼了盆冷水:让AI反复检查、批评、改写自己的答案,效果可能还不如最简单的“多试几次,选出现次数最多的答案”。科学家在1.5B到7B的不同规模模型上做了严格对比,统一计算生成的每一个词,结果发现,所有“自我反思”类方法都没有稳定胜出,甚至有十种明显更差。最有趣的发现是,让AI自己挑选最佳答案,反而不如机械地统计哪个答案出现最多,在小模型上差距明显,到了大模型上差距虽缩小,但也没带来额外好处。原因是AI在“反思”时会产生大量额外文字,而这些文字本身就帮它提高了准确率,真正起作用的不是“思考”,而是“多写”。更尴尬的是,有一款经典的反思方法在小模型上从不触发重试,每次都觉得自己答对了,实际上偷偷变成了普通回答。这项研究提醒开发者:与其给AI设计复杂的反思流程,不如老老实实多抽几次样,成本更低,效果还可能更好。
Methods that make a language model plan, criticise and rewrite its own answer, reflect on mistakes, pick the best of several attempts, or debate with copies of itself nearly all make it generate far more text than a single chain of thought. Because generating more text raises accuracy by itself, a gain over one chain of thought does not show the method's idea is what helped. Wang et al. (2024) reported that a simple baseline, sampling the same question repeatedly and keeping the most common answer, often wins once budgets are comparable, but gave point estimates with no confidence intervals or significance tests. We rerun that comparison as a designed experiment: seven methods, open models of 1.5B, 3B and 7B parameters, two mathematics benchmarks, 150 questions each. We count every generated token, including those spent on critiques, reflections, debate turns and checking, and compare each method against repeated sampling at its own measured cost. All 36 comparisons are paired by question, with bootstrap intervals and multiplicity correction. No method is reliably better than repeated sampling at equal cost anywhere. Ten are reliably worse, all of them methods where the model inspects its own output, and all 18 self-inspection comparisons are negative. The two kinds of self-inspection part company as models grow. Choosing stops hurting: taking Best-of-N's eight samples and just counting the most common answer beats letting the model pick by 8.0 and 11.3 points at 1.5B, but only 2.0 and 1.3 at 7B, no longer distinguishable from zero. Rewriting does not recover: Self-Refine and a forced Reflexion stay 3.6 to 10.1 points below baseline at 7B. Reflexion as published never triggered its own retry on the smallest model. It judged itself correct every time and silently became a single chain of thought. We release code, prompts, all generations, and our verification scripts.
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