The State of GPL Propagation to AI Models

Summary

When GitHub Copilot was launched in 2021, the fact that its training data included a vast amount of Open Source code publicly available on GitHub attracted significant attention, sparking lively debates regarding licensing. While there were issues concerning conditions such as attribution required by most licenses, there was a particularly high volume of discourse suggesting that the conditions of copyleft licenses, such as the GNU General Public License (GNU GPL), would propagate to the model itself, necessitating that the entire model be released under the same license. The propagation of the GPL is a concept that many modern software engineers have naturally accepted; thus, for an engineer with a straightforward sensibility, it is a perfectly natural progression to think that if GPL code is included in some form, copyleft applies and the license propagates. However, as of 2025, the theory that the license of the source code propagates to AI models trained on Open Source code is not seen as frequently as it was back then. Although some ardent believers in software freedom still advocate for such theories, it appears they are being overwhelmed by the benefits of AI coding, which has overwhelmingly permeated the programming field. Amidst this trend, even I sometimes succumb to the illusion that such a theory never existed in the first place. Has the theory that the license of training code propagates to such AI models been completely refuted? Actually, it has not. This issue remains an indeterminate problem where lawsuits are still ongoing and the judgments of major national governments have not been made clear. In this article, I will explain the current situation of this license propagation theory, namely “GPL propagates to AI models trained on GPL code,” and connect it to points of discussion such as the legal positioning of models and the nature of the freedom we pursue in the AI domain. The Current Standing in Two LawsuitsDoe v. GitHub (Copilot Class Action): T...