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Unlike previous versions of Office, individual security updates and other updates for Microsoft 365 Apps aren't available on Windows Update. Instead, every time that updates are released, Microsoft creates an updated version of Microsoft 365 Apps and puts it on the Microsoft 365 Apps CDN (officecdn.microsoft.com) on the internet. This updated version contains all the new updates, in addition to all updates from previous months. The update schedule depends on which update channel Microsoft 365 Apps is configured to use.
For a list when updates were released for Microsoft 365 Apps, see Update history for Microsoft 365 Apps.
To determine which version of Microsoft 365 Apps is installed on a user's computer, go to File > Account in any Office program. The version is listed under the About section. For example, in Excel, under the About Excel section.
Tip
The recommended approach is to let devices update directly from the Office CDN. You can also use Windows Server Update Services (WSUS) together with Microsoft Configuration Manager to update Microsoft 365 Apps. For more information, see Manage updates to Microsoft 365 Apps with Microsoft Configuration Manager.
Update process for Microsoft 365 Apps
There are three steps that occur automatically when the update process runs for Microsoft 365 Apps:
- Detect that updates are available
- Download the updates
- Apply the updates
Detect that updates are available for Microsoft 365 Apps
When you install Microsoft 365 Apps, a scheduled task called Office Automatic Updates 2.0 is created. This scheduled task is configured to look for updates on a regular basis. To see the schedule, open Task Scheduler on the device where Microsoft 365 Apps is installed, and then go to Task Scheduler Library > Microsoft > Office. On the properties of the Office Automatic Updates 2.0 task, look on the Triggers tab.
When the task runs, it compares the version of Microsoft 365 Apps on the computer to the version of Microsoft 365 Apps on the update ___location. The update ___location is where Office looks for updates, such as on a network share or from the internet. By default, Microsoft 365 Apps looks on the Office CDN on the internet for updates, but you can configure the update ___location. Devices that are enrolled in Cloud Update or managed by Intune can have the update ___location set automatically.
If there's a difference between the two versions, the update process determines which files are different and need to be updated on the local computer. After that, the next step, which is downloading the updates, starts.
Download the updates for Microsoft 365 Apps
Only the files that are different are copied down to a Download folder on the local computer, and they're downloaded in a compressed form. This helps reduce the size of the download.
The size of the download depends on several factors, such as how many updates are being released, and which version of Microsoft 365 Apps you're updating from. For example, if you have the March version of Microsoft 365 Apps installed, and you're updating to the July version, it's likely that more files are different between those two versions, than if you're updating from the June to the July version. Therefore, the download will probably be larger.
Note
Microsoft 365 Apps automatically chooses the smallest applicable package type (Full, File-delta, or Binary-delta). Binary-delta is typically used when the existing build is one or two releases behind.
Microsoft 365 Apps uses different package types depending on how far behind the client is:
| Package Type | Scenario | Typical Size |
|---|---|---|
| Full | First-time installation or when other packages aren't applicable | 1.5-2 GB |
| File-delta | When updating from 2-3 versions behind | 400-700 MB |
| Binary-delta | When updating from the previous 1-2 versions | 150-300 MB |
| Binary-delta-compressed | Optimal scenario - incremental update from latest previous version | 50-100 MB |
If the download process is interrupted, such as by a temporary loss of network connectivity, the download resumes after the interruption, instead of restarting from the beginning. After the updates are downloaded, the computer doesn't have to be connected to the internet or the network for the updates to be applied. That's because all the files that are needed to apply the updates are already on the local computer.
Bandwidth optimization
When a device retrieves updates from the CDN, Windows Delivery Optimization can peer-share content with nearby devices, dramatically reducing internet bandwidth. Delivery Optimization is on by default in Windows 11 Enterprise and Education.
If Microsoft Connected Cache is deployed, devices obtain the payload from the on-premises cache before reaching the CDN. This further reduces internet bandwidth usage while ensuring fast downloads for end users.
Apply the updates for Microsoft 365 Apps
After the compressed files are downloaded, Click-to-Run uncompresses and moves them from the Download folder to the Apply folder. The scheduled task then attempts to install the updates in the background, without requiring any user intervention.
The system can't apply updates if an Office program that needs updating is currently in use. In this case, the task tries to apply the updates the next time the scheduled task runs. If updates can't be applied for several days, users see a message that updates are ready to install. If the user restarts the computer and updates haven't been applied, the updates are applied as Windows starts. This won't prevent the user from logging in.
To make sure users apply updates, admins can configure a deadline. The deadline specifies a date and time by when the updates must be applied. If users don't apply the updates by the deadline, Office automatically closes any open Office programs and applies the updates. Users receive notifications leading up to the deadline.