Windows 10, version 21H1 for commercial pre-release validation

Published Mar 18 2021 10:00 AM 95.6K Views

Windows 10, version 21H1, is now available for commercial customers to begin feature exploration and validation prior to being released for general availability.

As previously announced, version 21H1 will be delivered to devices currently running Windows 10, version 2004 or version 20H2 using an enablement package. This is the same technology we used to update devices from Windows 10, version 2004 to version 20H2. Do you want to see how quickly devices update from version 2004 or 20H2 to version 21H1, and how little downtime is involved? Now you can!

You can access Windows 10, version 21H1 through all standard channels, including Windows Update, Windows Server Update Services (WSUS), and Azure Marketplace, or you can download an ISO file. The major build number is 19043. If you manage updates directly from Windows Update and have devices enrolled in the Release Preview Channel for validation purposes, you can go to the Windows Update Settings page of the device to download and install Windows 10, version 21H1 and experience the remarkably fast update that comes with updating via enablement package.



Note: We consider a device a commercial device if it is not running the Home edition of Windows 10, is being managed by an IT administrator (whether via Microsoft Endpoint Manager or a third-party MDM tool), or if the device has a volume license key, a CommercialID, or is joined to a domain.

As with Windows 10, versions  2004 and 20H2, version 21H1 also shares a common core operating system with an identical set of system files. New features are included in monthly quality updates for version 2004 in an inactive and dormant state. These new 21H1 features remain dormant until they are turned on through the “enablement package,” a small, quick-to-install “master switch” that activates the Windows 10, version 21H1 features.

If you are managing updates with WSUS, you have the option of taking a full feature update to 21H1 or testing out the enablement package path if your devices are currently running 2004 or 20H2. As with any other validation done on pre-release updates published to WSUS, you will need to first ensure that you have synced the “Windows Insider Preview” category. Once you have synced this category, you should see the following updates show up in your console as shown below:


To test out this experience on a virtual machine, check out the Windows 10 Preview on Azure Marketplace or, if you would prefer, you can download the Windows 10, version 21H1 ISO (build 19043).

We not only want to ensure that you have access to the upcoming Windows 10 feature update payload via any channel you may use today, we also want to enable you to validate with confidence. Therefore, customers in the Windows Insider Program for Business can once again receive Microsoft Support for the Windows 10, version 21H1 build available through WSUS, ISO download, Azure Marketplace, and directly from Windows Update in the Release Preview Channels.

If you run into a severe issue that prevents you or other users in your organization from using a device, or compromises security or personal data, use the online form to request assistance directly from Microsoft Support—at no cost to you.

For more information, check out these useful links for exploring and validating pre-release Windows feature updates:


Super Contributor

As we are using a third party system to distribute updates i went to check if Enablement Package can be downloaded from Windows Update Catalog and maybe deployed this way. But i don't see it there (say for 1909 version). Why is this so? If it is deployed with WU and WSUS, i thought it should be using similar mechanisms. Or is it that different that it can't be installed as a standalone msu/exe/etc.?

Occasional Visitor

There wont be an enablement package for this version as pre 20H1 versions require a full OS upgrade.  20H1+ works by the fact all the OS builds are the same but the enablement package switches on the new features.

Super Contributor

James990, you are contradicting what the article actually says. They say that you will be able to update to 21H1 with an enablement package if you are running 2004 or 20H2. Enablement package also existed when updating from 1903 to 1909 or from 2004 to 20H2.


@Oleg K msu files do exist for Enablement Packages (1909, 20H2, 21H1)
i can send you the download links if you want


Enablement Packages only require latest SSU version, they can be installed (staged) even before LCU

Valued Contributor

Thank you for sharing.

It is a good opportunity to start testing this build and then work on deployment.


@Oleg K James990 is correct. There isn't an EKB to go directly from 1909 (19H2) to 21H1. For 1909 you need to upgrade to 20H1+ (2004) then use an EKB to get to 21H1. 

Super Contributor

@abbodi1406i have see various articles on the web posting enablement package files, but i need a download source from MS, not some third party that we can't trust.


There is no Microsoft source to grab the EKB files directly. It's only available on WU or WSUS. Prerequisites are to update to the latest cumulative update and the Enablement KB will be offered. Or upgrade to 20H2 directly with Install media .  

Windows Feature update 


@Oleg K  The download links are from MS
but regardless the link source, if you can't trust the MS digital signature of the files, and the fact that Windows OS itself will not accept or install "untrusted" updates, then i guess you should stick with the official route (WU/WSUS)

Frequent Contributor

21H1 is a great release with many improvements. The good side and bad side is issues more and more affect many releases across releases, in special when using the same Core OS such as 1903 / 1909 or 2004 / 20H2, 21H2.
This also has a good side effect because the issues are more consistent in home or business environment that naturally aren't 100% running the same builds.

heads-up for PowerUsers or those that are running a Microsoft lab at home (likely using MS tech as a baseline)

:warning:Please be cautious to with 1903, 1909, 2004, 20H2, 21H2 when using Storage Spaces with ReFS formatted drives in the pool. Try to avoid running Defrag Optimization or to cause a "Storage pool full state"

Affected build (tested 02-2021)
Windows Server, version xxxx (SAC), Windows 10 Pro, Windows 10 Enterprise

Windows Insider Beta (21H2)


Not affected:

Windows Server 2019 LTSC 1809 17763.x
Windows 10 Insider Dev since b19628
Windows Server 2022 LTSC Preview 21H2 

Here is my original feedback
The first issue reports dated back 6-8 months before 1903 release but unfortunately cannot find it. 


Original issue deleting files on ReFS does not free up space on a Storage Spaces Pool (my feedback, which initiated the fix in Insider Dev)

other examples:,

factually related issue with Defrag Optimizing

Defrag bloating up space on optimizing or fail to optimize due to low space and this behaviour


other references:

Storage Spaces pool does not reclaim free space from deleted files (

Windows 10 2004: Storage Spaces issues | Born's Tech and Windows World (

Frequent Contributor

Another thing to consider for PowerUsers 


If one is using ReFS please know that your ReFS version will be upgraded on all attached volumes. There is no roll back. Also there is no tool known to me to convert an older ReFS to a newer version, so they should be attached if you are looking for optimal performance and new features. 


As there is no official version matrix this is the most comprehensive source.


Storage Spaces pool versions can be upgraded manually. Rollback isn't possible either. 




Occasional Visitor

The end of Enterprise support for 20H2 is 05/09/2023.  Every article I've read thus far assumes that since 21H1 is a spring release it automatically only gets 18 months of support, so only out to near the end of 2022, despite the fact that the very existence of 21H1 breaks the prior release pattern.  It seems illogical to me for Enterprise support for 21H1 to end before 20H2, regardless of the whole spring/fall 18/30 month support precedent (from Sep. 2018).  The most sense would be for 21H1 to get the same retirement date as 20H2.






Super Contributor

What do you mean by it breaking the pattern? 21H1 is what 2103 would be (same as 2004 or 1903). Unless you mean the fact that 21H1 can be installed as an Enablement package for 20H2 and 2004. This is a technology change, but i guess not warranting the process change. You can wait until 21H2 and install it, which will have longer support than 20H2. It was the same since they introduced different support terms. 1809 was (still is) supported longer than 1903, 1909 longer than 2004, etc.

Occasional Visitor

thank you very much

Occasional Visitor

Hello Sirs/Madams:

I have a latest version of windows 10 and fully updated to the latest update before Microsoft released feature update 21H1 today.
I have a 64 bit system and my only question is how many GB is the download because I am on a metered connection.
Thank you everybody and best wishes.


Super Contributor

Bashar, if you install Enablement Package it should be only a few MBs and it downloads and installs in a few seconds usually (aside the mandatory restart, which is also short in this case).

Frequent Contributor

I would like to recommend reading this summary and follow-up article

Occasional Visitor

If you are managing updates with WSUS, you have the option of taking a full feature update to 21H1 or testing out the enablement package

I would like to deploy with WSUS the full feature update to 2004 and 20H1 installations. But in WSUS only the enablement package is applicable to these installations. Can I somehow force the Update with WSUS also to 2004 and 20H1? I already rejected the enablement update, but that didn't help.

Reason is a full update fixes a problem we have with protected view in Office. The full feature update fixes the problem on installations with 1909 and older. On newer versions the enablement package does not fix it, only a manual update with the full iso does.

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Last update:
‎Mar 19 2021 07:24 AM
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