ZenML is and always will be open-source at its heart. The core framework is freely available on
Github and you can run and manage it in-house without using the Pro product. On the other hand, ZenML Pro offers one of the best experiences to use ZenML, and includes a managed version of the OSS product, including some Pro-only features that create the best collaborative experience for many companies that are scaling their ML efforts. You can see a more detailed comparison
here.