Updated March 16, 2022 to add clarity about the contents of out-of-band releases.
As we advance towards general availability of Windows 11 this holiday, we thought it was a good time for a refresher on Windows monthly quality updates. Windows monthly quality updates help you stay productive and protected. They provide consumers and IT administrators alike with the security fixes they need to protect devices before unpatched vulnerabilities can potentially be exploited. Monthly quality updates are cumulative and include all previously released fixes to guard against fragmentation of the operating system (OS), which can lead to reliability and vulnerability issues when only a subset of fixes is installed.
To ensure that this information is easy to find when needed, you can now find a topic on Monthly quality updates in our Windows technical documentation. It defines the different types of monthly quality updates – specifically B, C, and out-of-band (OOB) releases – and describes their role for consumers and enterprises alike. I'll also summarize that information here.
Update Tuesday – aka "B" releases
For many of you, Update Tuesday (also referred to as "Patch Tuesday") is a regular part of Windows servicing. Published on the second Tuesday of each month, our "B" releases are cumulative, including both new and previously released security fixes along with non-security content introduced in the prior month’s Preview “C” release (see below for details). These updates help keep Windows devices secure and compliant by deploying stability fixes and addressing security vulnerabilities.
“B” releases are mandatory and are available through our standard channels, which include Windows Update, Windows Server Update Services (WSUS), and the Microsoft Update Catalog.
Optional previews – aka "C" releases
If you want to test and/or validate production-quality releases ahead of the planned “B” release for the following month, you can leverage “C” releases, which are optional, cumulative, non-security preview releases. “C” releases are only offered for the most recent, supported versions of Windows. New features like News and Interests may initially be deployed in the prior month’s “C” preview release, then ship in the following month’s “B” release.
To access “C” releases, navigate to Settings > Update & Security > Windows Update and select Check for updates.
IT admins may also validate fixes and features in a preview update by leveraging the Windows Insider Program for Business or via the Microsoft Update Catalog.
Out-of-band releases may be provided to fix a recently identified issue or vulnerability. They are used in atypical cases, such as security vulnerabilities or a quality issue, when devices should be updated immediately instead of waiting for the next monthly quality update release. Out-of-band releases are cumulative, meaning that they include the updates from the previous “B” and/or “C” release as well as the additional fix.
As a general practice, we recommend that both consumers and commercial customers patch their devices as soon as possible. For IT admins, we also recommend taking advantage of “C” preview releases to internally validate releases ahead of the following month’s “B” release.
To help manage updates across your organization, be sure to also check out these resources:
If you are a Microsoft Partner or registered commercial customer, you can also take advantage of the Security Update Validation Program (SUVP), a quality assurance testing program geared toward the “B” release. SUVP partners can start testing these security updates three weeks prior to Update Tuesday and provide us with feedback regarding usability, bug reports, test reports, etc. For more details on the SUVP, see Security Update Validation Program: the early bird tests the worm.