Effective November 11, 2020, new constrained vCPU capable virtual machines are available from Microsoft. In this type of VM the vCPU count can be constrained to a half or a quarter of the original VM size. This allows customers to reduce the cost of software licensing, while maintaining the same memory, storage, and I/O bandwidth.
For instance, in the E8-4as v4 virtual machine there are 4 active vCPUs and 8 underlying vCPUs, and licensing for SQL Server is constrained to the active vCPU count, with only the operating system cost based on the underlying vCPUs.
For the announcement, please visit: https://azure.microsoft.com/en-us/updates/new-constrained-vcpus-capable-vms-now-available/.
For all the VMs of this type, and their pricing, search for “constrained” on this page: https://azure.microsoft.com/en-us/pricing/details/virtual-machines/windows/.