Manual annotation is just as burdensome as it is necessary for some legal text analytic tasks. Given the promising performance of Generative Pretrained Transformers (GPT) on a number of different tasks in the legal domain, it is natural to ask if it can help with text annotation. Here we report a series of experiments using GPT-4 and GPT 3.5 as a pre-annotation tool to determine whether a sentence in a legal opinion describes a legal factor. These GPT models assign labels that human annotators subsequently confirm or reject. To assess the utility of pre-annotating sentences at scale, we examine the agreement among gold-standard annotations, GPT’s pre-annotations, and law students’ annotations. The agreements among these groups support that using GPT-4 as a pre-annotation tool is a useful starting point for large-scale annotation of factors.