Abstract
When vendors relicense their open source projects under non-open source licenses, communities often respond with public backlash, forks, and concerns about long-term sustainability, but the concrete impact on contributor activity remains underexplored. We investigated how contributor activity levels change following such license changes in vendor-controlled open source projects. Using a case study approach, we analyze four projects—Schema Registry, Kibana, MongoDB, and Terraform—whose licenses were changed from OSI-approved licenses to non-open source licenses. Drawing on core-periphery and episodic contributing models, we classify contributors into core, regular, and occasional levels and distinguish between vendor-affiliated and external contributors. Using trace data from Git repositories collected via CHAOSS GrimoireLab, we compare contributor levels and affiliation in the year before and the year after each project's relicensing. Across cases, we observe that overall project activity is mostly stable or modestly declining rather than growing after relicensing, and vendor-affiliated contributors remain responsible for the majority of commits both before and after the change. We do not find evidence of a mass exodus of external core contributors; instead, we see redistribution across contributor levels, with some core contributors shifting to lower engagement and inactive contributors moving into active roles. Our findings suggest that relicensing may stall community growth.