Hello @Matt Britton
Thank you for reaching out to the Microsoft Q&A platform.
Unfortunately, it seems that only the Standard_D4s_v4 and Standard_D8s_v4 virtual machine sizes support nested virtualization in Azure Lab Services. If you require a virtual machine with 64GB of memory for your lab, you may want to consider using a different Azure service that supports nested virtualization, such as Azure Virtual Machines.
Azure Virtual Machines supports a wider range of virtual machine sizes, including sizes with up to 416 GB of memory. You can also use Azure Virtual Machines to create custom virtual machine sizes that meet your specific requirements.
Keep in mind that Azure Virtual Machines is a different service than Azure Lab Services, and it may require more setup and configuration to use. However, it may be a better option if you require a virtual machine with more memory than what is available in Azure Lab Services
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