Microsoft’s 25 July 2025 deadline was a procedural filing date, not a trial or payment deadline. The UK Competition Appeal Tribunal (CAT) has since certified Dr Maria Luisa Stasi’s proposed collective action on an opt-out basis. As of 18 August 2026, the case is continuing; the CAT has not found Microsoft liable and no damages have been awarded.
The latest position
The case is Dr Maria Luisa Stasi v Microsoft Corporation, Microsoft Limited and Microsoft Ireland Operations Limited, CAT case 1696/7/7/24. On 21 April 2026, the CAT granted a collective proceedings order (CPO), allowing the claim to proceed collectively. The tribunal’s case page records that Microsoft opposed certification.
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On 20 May 2026, the CAT refused Microsoft permission to appeal the certification decision. Microsoft renewed its application before the Court of Appeal; that application should not be described as a successful appeal or as having halted the CAT proceedings. A further CAT case-management conference is listed for 4 December 2026. The latest procedural information is on the CAT case page and in the CAT’s certification judgment.
What happened on 25 July 2025?
Microsoft was ordered to file its formal response to the proposed collective claim by 25 July 2025. It was a response to the application for collective certification, not a deadline to pay money, admit liability or attend trial. The claimant’s reply was reported as due on 10 October 2025, followed by a CAT hearing on 11–12 December 2025 to decide whether the action could proceed collectively. The original deadline was reported by Computer Weekly.
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What the claim alleges
The claim alleges that Microsoft used its position in Windows Server software and cloud services to disadvantage rival infrastructure providers. Its central allegation is that Windows Server licensing can be more expensive or less favourable when the software is run on AWS, Google Cloud, Alibaba Cloud or another non-Azure platform than when it is used on Microsoft Azure.
The pleaded legal theories include alleged abuse of a dominant position under the UK Chapter II prohibition and, for relevant historical periods, Article 102 of the Treaty on the Functioning of the European Union. The CAT’s claim-form summary describes the proposed class and the alleged licensing practices.
These are allegations, not established findings. The CAT’s CPO judgment decides whether the case can proceed collectively; it does not decide that Microsoft breached competition law.
Who may be covered?
The certified action concerns UK-domiciled organisations that obtained licences to use Windows Server from providers covered by the legally defined class. The alleged harm relates to using Windows Server on rival clouds, not to every Microsoft customer or every cloud workload.
- Potentially relevant arrangements may include volume licensing, licences obtained through a cloud provider, dedicated-host deployments, bring-your-own-licence and licence-included models.
- Azure Hybrid Benefit and other Microsoft licensing programmes may affect an organisation’s circumstances.
- Organisations outside the UK, or those using Microsoft products other than Windows Server, should not assume they are included.
- Customers that changed cloud platforms may need records covering each relevant period.
Later media reports have referred to about 59,000 British organisations, but that figure is not a substitute for the operative CPO and its class definition. Eligibility should be checked against the tribunal’s orders and any official claimant notices.
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What the CPO means
A collective proceedings order is the CAT’s permission for a competition claim to be managed on behalf of a defined group. This action is on an opt-out basis for the relevant class, so eligible organisations may fall within the proceedings without individually issuing a claim, subject to the order and any applicable procedures.
- It does mean: the claim can move to disclosure, evidence, case management and later determination as a collective action.
- It does not mean: Microsoft has been found liable, the alleged loss has been proved, or any organisation is guaranteed compensation.
- It does not set damages: any recovery would depend on proving the alleged conduct, causation and loss, followed by the tribunal’s orders on assessment and distribution.
How much money is claimed?
2025 coverage described the potential claim as approximately £2bn. Later reports used figures around £2.8bn, while a legal-sector summary referred to £1.7bn. These are estimates attributed to the claimant or reported descriptions of the case, not an award or an admitted liability. The amount may change as the pleadings, evidence and class definition develop.
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Dr Maria Luisa Stasi is the class representative. The legal team is associated with Scott+Scott UK LLP. The defendants are Microsoft Corporation, Microsoft Limited and Microsoft Ireland Operations Limited. Procedural documents are also made available through the claimant-side UK Cloud Licensing Claim documents page.
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The available procedural record shows that Microsoft opposed the CPO application. The 2025 report said Microsoft had not provided a response to Computer Weekly by publication. No definitive current Microsoft statement on the April 2026 certification is established in the materials available here, so claims about Microsoft’s views should be attributed to the CAT record rather than presented as an admission.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What happens next?
The action remains in litigation. The 4 December 2026 case-management conference is expected to address steps such as disclosure, evidence and preparation, although its precise agenda will depend on the latest CAT directions. The renewed appeal application is a separate procedural issue and should be followed through the CAT and Court of Appeal records.
What potentially affected organisations can do
Organisations should preserve records rather than assume that joining or compensation is automatic:
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- Microsoft licence agreements, amendments and Volume Licensing Statements.
- Cloud-provider invoices showing Windows Server charges.
- Deployment records identifying cloud platform, dates and workloads.
- Azure Hybrid Benefit or comparable entitlement records.
- Procurement correspondence about cloud selection, licensing restrictions or migration.
- Evidence of additional charges, technical restrictions or migration costs.
Keep the records secure and seek specialist competition-law advice before making eligibility decisions, changing licensing arrangements or relying on third-party claim services. The official CAT case page and claimant notices should take precedence over marketing claims.
Why the case matters for cloud buyers
The litigation tests whether software licensing terms can unlawfully disadvantage competing infrastructure providers. A claimant victory could potentially lead to damages and changes in commercial practice, affecting multi-cloud procurement, portability decisions and the cost of avoiding platform lock-in. Neither damages nor changes to Microsoft’s licensing are guaranteed.
The issue is relevant to public-sector and private-sector buyers comparing Azure with AWS, Google Cloud, Alibaba Cloud and other platforms. A cloud calculator or current invoice analysis can help reconstruct costs, but it cannot by itself establish historic competition-law liability.
How it differs from regulatory scrutiny
The private Stasi collective action is distinct from regulatory and industry scrutiny of cloud licensing. 2025 reporting discussed UK and European concerns about charging more when software runs on rival clouds, including a Google complaint to the European Commission and scrutiny involving UK authorities. Those developments provide context but are not findings in this damages claim.
A regulator’s investigation, a trade-group complaint and a private CAT action have different legal tests, parties and remedies. None should be described as proof that Microsoft has already been found liable in the Stasi proceedings.
Quick Recap
Procedural timeline
| Date | Event |
|---|---|
| 3 December 2024 | Stasi’s collective proceedings claim form was filed at the CAT. |
| 10 June 2025 | Computer Weekly reported the 25 July response deadline. |
| 25 July 2025 | Deadline for Microsoft’s response to the CPO application. |
| 10 October 2025 | Reported deadline for Stasi’s reply. |
| 11–12 December 2025 | CAT hearing on whether to grant the CPO. |
| 21 April 2026 | CAT granted the CPO and certified the claim on an opt-out basis. |
| 20 May 2026 | CAT refused permission to appeal; Microsoft renewed its application before the Court of Appeal. |
| 4 December 2026 | Next CAT case-management conference is listed. |
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