Important update: Access to instance size flexibility ratios is changing on 9 May 2026

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Important update: Access to instance size flexibility ratios is changing on 9 May 2026

Priya Jayaraman 326

|| | -------- | COMMUNICATION:

You're receiving this notification because you’re associated with one or more Azure subscriptions using Azure Virtual Machine Reserved Instances.

After 9 May 2026, the instance size flexibility ratio file will no longer be updated in our documentation. To access the latest instance size flexibility ratios, you’ll have to use the Azure Catalogs API. Read this documentation page for details on using the API.

You may continue using the current instance size flexibility file until 30 August 2026. However, if your organization relies on this file for internal billing processes or cost management tools, we recommend transitioning to the new API as soon as possible.

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If you have questions, get answers from community experts in Microsoft Q&A. If you have a support plan and need technical help, please submit a support request.

COMMUNICATION:

You're receiving this notification because you’re associated with one or more Azure subscriptions using Azure Virtual Machine Reserved Instances.

After 9 May 2026, the instance size flexibility ratio file will no longer be updated in our documentation. To access the latest instance size flexibility ratios, you’ll have to use the Azure Catalogs API. Read this documentation page for details on using the API.

You may continue using the current instance size flexibility file until 30 August 2026. However, if your organization relies on this file for internal billing processes or cost management tools, we recommend transitioning to the new API as soon as possible.

Help and support

If you have questions, get answers from community experts in Microsoft Q&A. If you have a support plan and need technical help, please submit a support request.

Priya Jayaraman 326 Reputation points

2026-04-09T08:56:29.5633333+00:00

Please kindly advice on this article
Suchitra Suregaunkar 11,635 Reputation points Microsoft External Staff Moderator

2026-04-09T10:07:35.12+00:00
Hello @Priya Jayaraman

Thank you for posting this query on Microsoft Q&A platform.

This notification refers only to a change in how Instance Size Flexibility (ISF) ratio values are accessed, and not to any change in the Reserved VM Instance (RI) feature or pricing logic.

Instance Size Flexibility (ISF) is an Azure Reservations capability that allows a single reservation purchase to automatically apply across multiple SKUs within the same flexibility group.

Within an instance size flexibility group Each SKU has a relative ratio, and these ratios are used to calculate how the reservation discount applies to the virtual machines you have running.

Microsoft has confirmed that:

The static Instance Size Flexibility ratio file currently published in Microsoft documentation will no longer be updated after 9 May 2026.

To retrieve the latest ISF ratio values, customers must use the Azure Catalogs API going forward.

This means that:

The ISF feature itself is not being retired or modified.

Reservation discount matching logic remains unchanged.

Only the method of accessing the ratio values is changing (from documentation file → API).

Microsoft has also communicated that:

Customers may continue using the existing documentation‑based ISF ratio file until 30 August 2026.

After this date, the documentation file will be deprecated and may no longer reflect the backend reservation discount application logic.

ISF ratios are used internally to normalize VM usage across different sizes within the same VM family when applying RI discounts.

The ratio column compares the relative footprint for each VM size in that instance size flexibility group and is used to calculate how the reservation discount applies to running VMs.

If an organization uses these ratios for:

Internal billing / showback / chargeback

Reservation utilization reporting

Cost optimization tooling

Custom RI coverage calculations

then continuing to rely on the static documentation file after 30 August 2026 may result in outdated calculations.

If your organization relies on ISF ratio values for internal cost management or billing processes, Microsoft recommends transitioning to the Azure Catalogs API to retrieve up‑to‑date ratio values before 30 August 2026.

This change does not impact:

Existing Reserved VM Instance purchases

Reservation pricing

Discount eligibility

Instance Size Flexibility feature behavior

It only impacts how ISF ratio data is accessed going forward.

Could you please let us know if the comment above resolved your issue? If you need any further assistance, feel free to reach out—we're always here to support you.

If you found the comment helpful, please consider clicking "Upvote it."

Thanks,

Suchitra.

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Priya Jayaraman 326 Reputation points

2026-04-09T08:56:29.5633333+00:00

Please kindly advice on this article

Answer 1

The communication means that the static CSV file with instance size flexibility (ISF) ratios in the documentation will stop being updated after 9 May 2026, and will be fully deprecated for use after 30 August 2026. The ISF feature itself is not being removed; only the way to obtain the ratios is changing.

Key impacts and required actions:

What is changing

The current ISF ratio CSV file referenced from the “Virtual machine size flexibility with Reserved VM Instances” documentation will no longer receive updates after 9 May 2026.
After 30 August 2026, relying on that CSV for accurate ratios is not recommended; it may be outdated relative to new or changed SKUs.
Going forward, the authoritative source for ISF ratios will be the Azure Reservations Catalogs API (Azure Catalogs API).

How to get ISF ratios going forward

Use the Azure Reservations Catalogs API to retrieve ISF data programmatically.
The API returns, per SKU, the ISF metadata in skuProperties:
- InstanceSizeFlexibilityGroup (or ReservationsAutofitGroup in some responses) – the flexibility group name (for example, “Av2 Series”, “General Purpose Gen5”).
- InstanceSizeFlexibilityRatio (or ReservationsAutofitRatio) – the ratio value used for ISF calculations.
The “Instance size flexibility (ISF)” documentation describes how to:
- Call the Catalogs API for the relevant reservedResourceType (for example, Virtual Machines).
- Parse the response and construct a CSV with columns:
  - InstanceSizeFlexibilityGroup
  - ArmSkuName
  - Ratio

Recommended next steps for cost management/billing tools

If any internal billing, showback/chargeback, or cost optimization tooling currently reads the public CSV file directly or uses a copy of it:
1. Implement a scheduled job (for example, PowerShell or another client) that calls the Azure Reservations Catalogs API.
2. Parse skuProperties to extract the ISF group and ratio for each ArmSkuName.
3. Generate and store an internal CSV or table in the same structure currently used by your tools (InstanceSizeFlexibilityGroup, ArmSkuName, Ratio).
4. Update downstream tools to read from this new internal source instead of the public documentation CSV.
Follow the guidance in the ISF documentation about:
- Pagination via nextLink.
- Region-specific data (ratios can vary by region, so generate per-region files if needed).
- Regular updates, because ratios may change as new VM sizes are introduced.

Relation to reservations and VM retirements

ISF continues to apply to Azure Virtual Machine Reserved Instances as before: reservation benefits can be shared across sizes within the same flexibility group using the ratio values.
For VM sizes that are retiring (for example, certain families listed in the “Azure Virtual Machine size retirements in 2026” article), ISF ratios for replacement SKUs can be obtained via the same Catalogs API, which helps plan reservation coverage when migrating to suggested replacement sizes.

Support

For complex scenarios (for example, large internal billing systems or cross-region reservation optimization), open an Azure support request as suggested in the communication, or use Microsoft Q&A for community guidance.

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Important update: Access to instance size flexibility ratios is changing on 9 May 2026

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