The license key is valid for one domain, its subfolders(sub applications based on Sitefinity) and its subdomains. The license key for Sitefinity 3.x is not valid for 4.x edition.
All the best,
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items