57% of paraphrase gradients in a prompt-mixing training set disagreed in sign
AspireAI community · arXiv
Models are highly sensitive to prompt wording, and the usual fix is inference-time prompt optimisation, which is manual and does not scale. This work pushes prompt robustness into training instead, and starts from an observation about the standard remedy of mixing paraphrases of each prompt into training: across trainable parameters, the per-paraphrase gradients interfere, with 57% exhibiting sign conflicts, and the naive gradient average discards roughly a fifth of the magnitude. The authors develop two gradient-merging methods, Prompt-TIES and Prompt-DARE, that resolve the interference using operators from model and gradient merging. Across four models from two families at two scales, the interaction between prompt phrasing and the specific examples accounts for 54% of per-example variability on average and exceeds 70% on ANLI and WiC. The merging methods nearly halve per-example variance on fully fine-tuned models at little cost to overall accuracy, while the other train-time methods the authors compared improve raw performance but fail to improve variance reliably. Note this is a master's thesis whose parts also appear in an EMNLP 2026 paper, and checkpoints are released.
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