The Windows Server operating systems are licensed according to the core license model in Cloud Servers.
The number of core licenses required is based on the number of cores per server. Each core requires a license. If you increase the number of cores used, then you require additional licenses. The additional licenses are invoiced automatically.
For the servers created before 11/30/2016, the Windows license will be charged flat-rate. If you reinstall the operating system on this server, the Windows license will be licensed according to the Core license model.