December 31, 2026 is the final day Microsoft will provide security patches and technical support for Office Online Server. The announcement, posted to the Microsoft Tech Community, confirms there is no Extended Security Updates programme for OOS. Organisations still running it have roughly six months to plan a transition before the product becomes an unsupported risk on their network.
What Office Online Server does
Office Online Server is an on-premises server product that enables browser-based viewing and editing of Word, Excel, PowerPoint, and OneNote documents across SharePoint Server, Exchange Server, and Skype for Business Server. It allows users to open Office files in a browser without installing an Office client locally, and supports co-authoring directly within the SharePoint document library interface.
OOS is the successor to Office Web Apps Server and has been the standard browser-editing companion for SharePoint Server deployments for several years. Microsoft's retirement decision reflects a deliberate shift toward cloud-first productivity: the company has no plans to build a next-generation on-premises replacement.
The retirement timeline
| Date | What changes |
|---|---|
| Now through December 31, 2026 | OOS continues to function and receive security patches on the normal schedule |
| December 31, 2026 | End of all support: no further security patches, bug fixes, or Microsoft technical support |
| Post-December 31, 2026 | OOS may continue to run but is fully unsupported; unpatched vulnerabilities will accumulate with no vendor remediation |
Sources: Microsoft Tech Community - Announcing the retirement for Office Online Server
What stops working after the deadline
The OOS service itself does not switch off on a set date. It will keep running after December 31, 2026 until something breaks it: an incompatible SharePoint Server SE update, a Windows Server patch that conflicts with OOS internals, or a newly discovered and unpatched vulnerability. The risk compounds over time.
Functionality that depends on OOS in a typical SharePoint Server deployment:
- Browser-based preview and editing of Office documents stored in SharePoint document libraries
- In-browser co-authoring on Word, Excel, and PowerPoint files through SharePoint
- Integrated Office document previews in Exchange Server (where configured)
- High-fidelity document thumbnails in SharePoint search results
Core SharePoint functionality, including navigation, metadata, search indexing, workflow, and list management, does not depend on OOS and remains unaffected.
Microsoft's recommended paths forward
Microsoft has outlined three migration paths for organisations currently running OOS:
- Migrate to Microsoft 365. Moving SharePoint content to SharePoint Online eliminates the OOS dependency entirely. Browser-based document editing in Microsoft 365 is provided by the Microsoft 365 app platform, maintained in the cloud and updated continuously.
- Hybrid Microsoft 365 model. Organisations that need to retain some on-premises workloads can move Office app hosting to Microsoft 365 while keeping selected data on SharePoint Server SE.
- Microsoft 365 Apps for Enterprise or Office LTSC 2024. For environments that cannot move to the cloud, fully-installed Office client applications on user devices replace the browser-editing capability OOS provided. This requires a client deployment rather than a server-side change.
Planning a move to SharePoint Online
For organisations that have been considering a migration from SharePoint Server to SharePoint Online, the OOS retirement provides a concrete deadline for a project that might otherwise have drifted. Moving content to SharePoint Online removes the OOS dependency, eliminates the on-premises server maintenance burden, and delivers browser-based document editing through Microsoft's continuously updated cloud platform.
A content migration to SharePoint Online typically involves moving document libraries, lists, and associated metadata. The guide to migrating a SharePoint site to another tenant covers the key steps. For consultants and admins managing the file migration itself, Clone Master handles full-fidelity library and site migrations to SharePoint Online without complex scripting, including cross-tenant scenarios.
Frequently Asked Questions
When does Office Online Server retire?
Microsoft will retire Office Online Server on December 31, 2026, after which it receives no security patches, bug fixes, or technical support. No Extended Security Updates programme has been announced.
Does the OOS retirement affect SharePoint Online?
No. Office Online Server is a strictly on-premises product. SharePoint Online and all Microsoft 365 cloud services are unaffected - browser-based editing in the cloud runs through Microsoft 365 apps, maintained separately from any on-premises component.
What replaces Office Online Server?
Microsoft recommends migrating to Microsoft 365, adopting a hybrid model, or deploying Microsoft 365 Apps for Enterprise or Office LTSC 2024 for local client editing. The right path depends on how much of the organisation's infrastructure can move to the cloud before the December 2026 deadline.