Due to privacy or commercial constraints, large pre-trained language models (PLMs) are often offered as black-box APIs. Fine-tuning such models to downstream tasks is challenging because one can neither access the model's internal representations nor propagate gradients through it. This paper addresses these challenges by developing techniques for adapting PLMs with only API access. Building on recent work on soft prompt tuning, we develop methods to tune the soft prompts without requiring gradient computation. Further, we develop extensions that in addition to not requiring gradients also do not need to access any internal representation of the PLM beyond the input embeddings. Moreover, instead of learning a single prompt, our methods learn a distribution over prompts allowing us to quantify predictive uncertainty. Ours is the first work to consider uncertainty in prompts when only having API access to the PLM. Finally, through extensive experiments, we carefully vet the proposed methods and find them competitive with (and sometimes even improving on) gradient-based approaches with full access to the PLM.

本文提出了一种适应预训练语言模型的技术，这种技术在只有 API 访问的情况下，通过软提示调整的方法进行微调，并且不需要访问 PLM 的任何内部表示，同时学习的提示分布可以量化预测的不确定性。通过大量实验证明这种方法可以和基于梯度的完全访问PLM方法相竞争甚至超过它们。

可靠的免梯度和免似然函数提示调整