How to update Office Online Server

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Office Online Server arrived with SharePoint Server 2016 and replaces Office Web Apps Server for SharePoint 2013. Office Online Server also receives updates, but the update procedure differs from SharePoint Server.

First, distinguish between a base installation release and subsequent updates. When moving to a newer base release, uninstall the existing installation and reinstall the product. When installing an update for the existing supported base build, do not uninstall the product. In both cases, however, first remove the server being updated from the farm, then recreate the farm or join the server to an already updated farm. Microsoft describes the procedure in Apply software updates to Office Online Server.

Support for Office Online Server ends on 31 December 2026. After that date, Microsoft will no longer provide security updates, fixes, or technical support. Alongside regular updates, plan your transition to a supported solution. See Microsoft’s Office Online Server retirement announcement for details.

Version

When updating Office Online Server, distinguish between the base installation build and the version after installing updates. The following table lists base builds, rather than individual CUs.

Base build Released End of support
16.0.6814.2226 4 May 2016 18 November 2016
16.0.7601.6800 18 November 2016 18 April 2017
16.0.7766.8550 18 April 2017 8 November 2017
16.0.8471.8525 8 November 2017 30 November 2018
16.0.10338.20039 30 November 2018 31 December 2026*

Source for builds and historical dates: Office Online Server release schedule. Verified on 17 October 2026.

* The Microsoft Learn table still lists TBD for the latest base build. The date of 31 December 2026 shown here comes from Microsoft’s announcement of the retirement of the entire product. A supported installation must also have the applicable updates, the base build alone is not sufficient.

You can check the base build in Control Panel – Programs and Features. To check the version after updates, follow Microsoft’s instructions and run the following command in an administrator PowerShell window:

Get-Content 'C:\ProgramData\Microsoft\OfficeWebApps\Data\local\OfficeVersion.inc'

Office Online Server - Version

Preparing to update Office Online Server

Check the version and update prerequisites

Compare the base build with the table and check the prerequisites in the KB article for the specific update. The latest base build listed in Microsoft’s release schedule is 16.0.10338.20039. If you are using an older installation release, prepare to move to the current base release and then install the applicable update.

The error The expected version of the product was not found on the system. does not, by itself, prove that you are using an old base release. Check the installed product and the requirements of the specific package rather than relying only on the error message.

Office Online Server - Expected version not found

Do not install Office Online Server updates automatically. Microsoft does not support this approach, because installation requires the procedure below, including removing the server from the farm. Updates also update the installed language packs, there are no separate language pack updates.

Select the update package for Office Online Server in the Microsoft Update Catalog or use the download link in its KB article. Download the required installation media, language packs, and updates in advance. Check the KB for prerequisites, known issues, and update replacement information. Generic KB wording about automatic installation does not replace the specific OOS farm update procedure.

If you already have the current base release, continue with Installing an update (CU). Use Installing a new base release when moving from an older base release. Before reinstalling, also check the operating system and required components against Deploy Office Online Server. Use the same updates and install all language packs in use on every server in the farm.

Save the current configuration

Before you begin, save the farm configuration. It will help you prepare the deployment script and compare the state before and after the update. Run PowerShell as an administrator and make sure the destination folder exists.

Import-Module OfficeWebApps
Get-OfficeWebAppsFarm | Format-List * | Out-File 'C:\OfficeOnlineServer.txt'
Get-OfficeWebAppsExcelBIServer | Format-List * | Out-File 'C:\OfficeOnlineExcelBI.txt'
Get-OfficeWebAppsExcelUserDefinedFunction | Format-List * | Out-File 'C:\OfficeOnlineExcelUserDef.txt'
Get-OfficeWebAppsHost | Format-List * | Out-File 'C:\OfficeOnlineHosts.txt'

These exports are references for restoring the configuration, rather than an executable restore script. Also record the certificates, internal and external URLs, load balancer settings, and custom farm parameters you use. After recreating the farm, re-add any configured data model servers for Excel Online and restore your UDF definitions and host allow list. See the OfficeWebApps module documentation for the available commands.

Prepare the deployment script

The Remove-OfficeWebAppsMachine command removes the current server from the farm. For a single server, recreate the farm with New-OfficeWebAppsFarm. For multiple servers, create the updated farm on the first server and join the remaining updated servers to it.

Prepare the deployment script in advance using the actual configuration. Microsoft recommends HTTPS even for internal environments. The following examples assume a certificate installed on the server, with its friendly name supplied through -CertificateName. Adjust the example names and parameters to match your farm.

Example with internal access over HTTPS:

New-OfficeWebAppsFarm -InternalUrl "https://oos.contoso.com" -CertificateName "OfficeWebApps Certificate" -EditingEnabled

Example with internal and external access over HTTPS:

New-OfficeWebAppsFarm -InternalUrl "https://oos.contoso.com" -ExternalUrl "https://office.contoso.com" -CertificateName "OfficeWebApps Certificate" -EditingEnabled

The -EditingEnabled parameter enables editing when used with SharePoint Server and the appropriate licensing. The certificate must cover the names in use. These examples assume HTTPS all the way to Office Online Server, SSL offloading requires configuration appropriate to the actual topology. See Deploy Office Online Server and the New-OfficeWebAppsFarm documentation for details.

Office Online Server update procedure

A single-server farm requires downtime for viewing and editing documents. For an HA farm, remove the server being updated from the load balancer before removing it from the farm. The original servers can continue handling traffic while you prepare the updated farm. Switch traffic only once the updated farm has enough capacity and passes the checks. Do not join servers with different update levels to the same farm.

Installing a new base release – First server

  1. If you use a load balancer, remove this server from its pool.
  2. Remove the current server from the farm in an administrator PowerShell window: Remove-OfficeWebAppsMachine.
  3. Verify that server removal has completed and that the Office Online Server web applications have been removed from IIS.
  4. Uninstall Office Online Server and its installed language packs.
  5. Restart the server.
  6. Install the current Office Online Server base release using installation media available under your licensing entitlement. The former VLSC functions have moved to the Microsoft 365 admin center, see access to Volume Licensing.
  7. Install the matching language packs, then the current update for this release. Check the prerequisites in the relevant KB article.
  8. After installation, restart the server as required by the installer.
  9. Create the farm using your prepared New-OfficeWebAppsFarm command and restore custom configuration, including your Excel Online settings and host allow list.
  10. Perform the checks in Verification after the update.

Installing a new base release – Additional servers (HA)

  1. Remove the next server from the load balancer and from the original farm: Remove-OfficeWebAppsMachine.
  2. Verify that removal has completed and uninstall Office Online Server and its language packs.
  3. Restart the server, install the same base release, matching language packs, and the same update as on the first server. Restart as required by the installer.
  4. Check the required certificates and join the updated farm. Use the name of a server that is already a member of that farm: New-OfficeWebAppsMachine -MachineToJoin "oos01.contoso.com".
  5. Perform the checks after the update. Once the updated farm has enough capacity, switch load balancer traffic to it.
  6. Repeat the procedure for the remaining servers.

Installing an update (CU) – First server

  1. If you use a load balancer, remove this server from its pool.
  2. Remove the current server from the farm: Remove-OfficeWebAppsMachine.
  3. Verify that removal has completed and install the applicable update. Do not uninstall Office Online Server for a normal update.
  4. Restart the server as required by the installer.
  5. Create the updated farm using your prepared New-OfficeWebAppsFarm command and restore custom configuration.
  6. Perform the checks after the update. Switch HA farm traffic only when the updated farm has enough capacity.

Installing an update (CU) – Additional servers (HA)

  1. Remove the next server from the load balancer and from the original farm: Remove-OfficeWebAppsMachine.
  2. Verify that removal has completed, install the same update as on the first server, and restart as required by the installer.
  3. Join the updated farm: New-OfficeWebAppsMachine -MachineToJoin "oos01.contoso.com".
  4. Perform the checks after the update and add the verified server to the updated farm’s pool.
  5. Repeat the procedure for the remaining servers.

Verification after the update

For an HA farm, check that the remaining original servers can handle traffic before removing the first server. Before switching traffic, verify the updated nodes and their configuration. If you test discovery through the farm URL, test routing must lead to the updated farm while preserving the correct hostname and certificate validation. Before the load balancer switch, the normal farm URL may still point to the original servers, so that test does not verify the updated farm. During the controlled switch, also run a functional test through the host application and check each additional node before adding it to the pool.

On each server, check the version and farm membership:

Get-Content 'C:\ProgramData\Microsoft\OfficeWebApps\Data\local\OfficeVersion.inc'
Get-OfficeWebAppsMachine
Get-OfficeWebAppsFarm

Open the farm’s discovery endpoint in a browser, for example https://oos.contoso.com/hosting/discovery. It must return WOPI discovery XML. Endpoint availability alone is not sufficient, open a real document through the connected host application and, depending on the features you use, also check editing and external data access in Excel Online. Check the restored custom settings and functionality after switching load balancer traffic.

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