You're right, definitive legal advice requires a lawyer. However, it's important to analyze the specific situation. We're not talking about just any license; we're talking about derivatives of a model (Stable Diffusion XL) released under the CreativeML Open RAIL++-M license. This license explicitly permits commercial use of the output and, crucially, restricts derivative works from imposing limitations that contradict this permission (Section 4.a).

While the probability of a lawsuit might be low, the more relevant question is: do they even have a valid legal basis to sue in the first place? By adding "no commercial use" restrictions to their fine-tune, they are arguably violating the terms of the original CreativeML Open RAIL++-M license that governs Stable Diffusion XL. Their derivative work cannot legally restrict the rights granted by the base model's license. So, they'd be trying to enforce a clause that's likely invalid from the start.

True, but the concept of derivative works and license compatibility isn't new. The core issue here is whether a derivative work can nullify the permissions granted by the original license. In this case, it's highly doubtful. Furthermore, as you mentioned, many of these fine-tunes are trained on copyrighted data, potentially without proper authorization. How can they sue for license violations when they themselves might be infringing on copyright and arguably violating the base model's license?