Mean Accuracy Is the Wrong Estimand for a Release Decision

arXiv:2610.16825v1 Announce Type: new Abstract: A release decision about a fine-tuned model is an operational commitment about the next rerun of its training recipe. Yet standard benchmark reporting gives only the mean accuracy of past seeds. These target fundamentally different questions: release decisions depend on catastrophic tail risk, whereas standard evaluation reports only central tendency. Because fine-tuning induces bimodal mode collapse, high average accuracy frequently conceals severe failure rates. Auditing 2,124 fine-tuned models across eleven language models, we show that shipping models based on mean accuracy violates a 10% deployment failure budget 48.0% of the time. Common heuristics like ar b - 2sigma prove equally dangerous: by underestimating variance on small samples, they become most permissive when evidence is weakest. We introduce extbf{recipe cards}, an evaluation framework that directly certifies rerun tail failure rates using exact finite-sample binomial bounds. Recipe cards reduce held-out budget violations to 0.6%, enforce a mathematical sample floor (N ge 22) that prevents certification on thin evidence, and explicitly refuse unverified claims under domain and task shifts.

Source: arXiv cs.LG | 2026-10-14