Premium OS licences billed per vCPU-hour.
A separate charge for the operating system licence on VMs running RHEL, SUSE, Windows Server, or SQL Server. It is billed per vCPU-hour on top of the compute charge, so it scales with instance size and can quietly exceed the compute cost on large instances.
Billed: Per vCPU-hour, on top of the instance charge. Rates vary by OS and sometimes step at 4+ vCPUs.