[Compute] Add Flow VMs (FlexProfile) support to az vm #34222

Preconditions

• No need to upgrade Python SDK or the Python SDK is ready.

Related command

• az vm update (urgent fix, see below)
• az vm create --preferred-size
• az vm update --preferred-size
• az vm show / az vm list (output gains flexProfile)

Resource Provider

Microsoft.Compute/virtualMachines

Description of Feature or Work Requested

[Public Preview]
Add Azure CLI support for Flow VMs (API name: FlexProfile), introduced in Compute API version 2026-04-01. A customer states a preferred VM size instead of an exact one. When the preferred size is constrained by capacity or placement, Azure may deploy a compatible alternative size. The VM records the request in properties.flexProfile.preferredVMSize and reports the deployed size in properties.hardwareProfile.vmSize. Using it requires the subscription feature Microsoft.Compute/FlexProfileEnabled and a supported region.

Urgent: az vm update removes FlexProfile today. az vm update does a GET and then a PUT through the AAZ model for 2026-04-01 (aaz/latest/vm/_update.py: VirtualMachinesGet, then VirtualMachinesCreateOrUpdate). That model has no flexProfile, and the AAZ loader skips fields the model doesn't define (azure-cli-core/aaz/_field_type.py, "ignore undefined key"). So the PUT is sent without flexProfile, which the service treats as an opt-out. Any az vm update on a Flow VM, even a tag change, silently takes it off FlexProfile. Regenerating the AAZ VM model from the merged spec at 2026-04-01 fixes this. No API-version change is needed, since az vm already uses 2026-04-01.

API rules the commands must respect:

• A request that adds flexProfile to a VM that doesn't use it yet must not include hardwareProfile.vmSize. The service rejects it with InvalidParameter.
• On a VM that already uses FlexProfile, a hardwareProfile.vmSize equal to the deployed size is ignored, so a GET body can be sent back unchanged. A different size is rejected with InvalidParameter.
• To stop using FlexProfile, send a PUT that omits flexProfile and sets hardwareProfile.vmSize. This pins the VM to that size.

Proposed command changes:

• az vm create: new --preferred-size, mutually exclusive with --size. --size has a default today, and _template_builder.py always sets hardwareProfile.vmSize. With --preferred-size, the template sets flexProfile.preferredVMSize and leaves out hardwareProfile.vmSize. Steps that depend on the VM size use the preferred size.
• az vm update: keeps flexProfile on ordinary updates after the AAZ regeneration. New --preferred-size sets or changes the preferred size, and also switches a VM that doesn't use FlexProfile yet. When it's used, the PUT leaves out hardwareProfile.vmSize.
• Opt-out: az vm update --size <size> --remove flexProfile.
• az vm show / az vm list: output gains flexProfile after the AAZ regeneration.
• Please also check az vm resize and any other command that sends a full VM PUT.

The PowerShell design with the same behaviour rules is https://github.com/Azure/azure-powershell-cmdlet-review-pr/issues/1578.

Minimum API Version Required

2026-04-01

Swagger PR link / SDK link

Azure/azure-rest-api-specs#46694

Request Example

• https://github.com/Azure/azure-rest-api-specs/blob/main/specification/compute/resource-manager/Microsoft.Compute/Compute/Compute/examples/2026-04-01/virtualMachineExamples/VirtualMachine_Create_WithFlexProfile.json
• https://github.com/Azure/azure-rest-api-specs/blob/main/specification/compute/resource-manager/Microsoft.Compute/Compute/Compute/examples/2026-04-01/virtualMachineExamples/VirtualMachine_Get_WithFlexProfile.json
• https://github.com/Azure/azure-rest-api-specs/blob/main/specification/compute/resource-manager/Microsoft.Compute/Compute/Compute/examples/2026-04-01/virtualMachineExamples/VirtualMachine_Update_WithFlexProfile.json

Target Date

2026-11-10

PM Contact

Lavanya.Krishnan@microsoft.com

Engineer Contact

Sri Harsha Varma Varma Uppalapati (@suppalapati-microsoft)

Additional context

The az vm update fix (AAZ model regeneration) is the most urgent part, because it affects Flow VMs created through the API, SDKs or PowerShell.