On October 23, 2025, Microsoft announced the public preview of Azure Virtual Machine (VM) vCore Customization, a new feature that gives users more control over the Central Processing Unit (CPU) resources of their Azure VMs. This preview introduces two main options – the ability to disable Simultaneous Multi-Threading and the ability to choose a custom number of VM virtual cores (vCores). Together, these features help optimize VM performance and adjust software licensing needs. Azure VM vCore Customization is currently available in public preview in select Azure regions (for example, West Central US, North Europe, East Asia, and UK South). Users can try these settings when creating a new VM via the Azure portal or other deployment tools. Since it is a preview release, the feature set may expand and is subject to change before general availability.
What is Azure VM vCore Customization?
Azure VM vCore Customization is a new capability that lets you adjust how many processing threads and virtual CPU cores are active in an Azure VM. In a standard Azure VM, each vCore (virtual CPU core) usually leverages Simultaneous Multi-Threading (SMT) — a technology where each physical CPU core runs two threads (often called hyper-threading). Until now, the number of vCores in a VM was fixed per VM size and SMT was always on by default. Azure VM vCore Customization changes this by offering two configurable settings:
- Threads Per Core (SMT setting): You can turn off SMT to run the VM with only one thread per physical core (i.e. disable hyper-threading).
- Custom vCPU Count (Constrained vCores): You can choose a lower number of active vCPU cores for a VM than the default for that VM size.
By using these settings, administrators and users can fine-tune a VM’s CPU configuration without altering other resources like memory, storage, or networking.
Key Features
- Disable Simultaneous Multi-Threading (SMT): This feature allows you to configure a VM to use one thread per CPU core instead of the usual two. In simple terms, it turns off the hyper-threading feature of the VM’s processor. With SMT disabled, each core is dedicated to a single task at a time, which can improve performance consistency for certain workloads. All other VM specifications (memory, disk, etc.) remain the same, but the VM’s operating system will see half the usual number of logical processors because each core is no longer split into two threads.
- Custom vCore Count (Configurable vCPUs): This feature lets you select a custom number of virtual CPU cores for a new VM that is fewer than the normal default for that VM size. In practice, you might deploy a VM type that typically has, say, 8 vCPUs, but configure it to use only 4 vCPUs. The VM still provides the full memory, storage, and input/output capacity of the 8-vCPU size, but only 4 cores are active. This is useful if your applications or licensing requirements only need 4 cores – you are not paying for unused software licenses on extra cores. It gives you granularity to match the VM’s CPU allocation to your actual needs.
(Note: “vCPU” or vCore refers to a virtual CPU core allocated to your VM. Disabling SMT or reducing vCPU count does not change the physical hardware, but it changes how many CPU threads/cores the VM can use.)
Licensing
From a licensing perspective, Azure VM vCore Customization is especially valuable. Many enterprise software products (for example, database servers like Microsoft SQL Server) are licensed per CPU core. By using the custom vCore count feature, you can limit the number of active cores in your VM to match the number of software licenses you have. This means you only pay for the software licenses you actually need, potentially significantly reducing licensing costs for core-based licensed software. For instance, if you run a SQL Server instance on a VM and only enable 4 vCores instead of 8, you would typically need licenses for 4 cores instead of 8 for that SQL Server deployment.
It is important to note that reducing the vCore count does not reduce the Azure VM’s infrastructure price – the cloud cost for the VM itself remains the same as if all cores were enabled.
The advantage is in the savings on third-party or Microsoft software licensing fees, not the Azure VM rental fee. In other words, you gain cost efficiency on licenses while maintaining the performance benefits (memory, bandwidth) of a larger VM size.
As with any licensing adjustments, it’s wise to get professional guidance. The experts at SCHNEIDER IT MANAGEMENT recommend reviewing your licensing agreements and provide advice to ensure compliance. We help you determine the optimal VM configuration, so you maximize cost savings without violating license terms. Always double-check with licensing specialists if you plan to alter core counts for compliance reasons.
More information
For additional details, please refer to the original sources and guidance:
- Official Microsoft announcement: https://techcommunity.microsoft.com/blog/azurecompute/announcing-preview-of-vcore-customization-disable-multithreading–configurable-c/4462417
- Azure Learn documentation on VM vCore Customization: https://learn.microsoft.com/en-us/azure/virtual-machines/vm-customization
SCHNEIDER IT MANAGEMENT is available for more information and expert advice on Azure VM vCore Customization. If you have questions about how this preview feature can benefit your organization or need guidance on licensing and implementation, feel free to reach out to their team for support.
