GitLab follows a true-up model that allows you to have more users than you paid for, and then pay for them when you renew your license. You can read more about it on our license FAQ.
All of the features and benefits of the different GitLab offerings can be found on the products page.
You can see all the differences between GitLab and other popular Git solutions on our comparison page.
GitLab Libre is open source and completely free for anyone to use. We don’t currently offer any discounts for the Enterprise subscriptions.
If you want to upgrade from GitLab Libre to one of the Enterprise subscriptions, you can follow the guides in our documentation.