The Windows 11 on Arm ISO Conundrum (Premium)

Among the many issues with Windows 11 on Arm is that Microsoft doesn’t make ISO image files available for download: Yes, you can get pre-release Windows Insider Program-based ISOs, but those change continuously, and they don’t represent final, shipping versions of the product.

This has to change.

I suspect it will: Microsoft maintains easily-Googled download sites for its supported, mainstream Windows versions, Windows 11 and Windows 10. Each provides a way to download the Windows Setup disks in image file (ISO) form, albeit only in x64/x86 forms. (The options vary by system.) But nothing for Arm, despite the fact that Windows 10 on Arm dates back to 2017 in stable. And Windows 11 on Arm has been available since that system first shipped in 2021.

But here we are, in this weird slice of time.

This slice in time is marked by two intertwined anomalies. Windows 11 version 24H2 is available publicly as I write this, but only on new (Arm64-based) Snapdragon X Copilot+ PCs like the Surface Laptop 7, Yoga Slim 7x, and EliteBook Ultra I’m now testing: Microsoft will continue testing 24H2, and will presumably add new features, before it’s second and more widespread release in October, one that will go out to all supported PCs, including the vast majority based on x64 (Intel and AMD).

Back in May, I wrote a tip describing how one could upgrade to Windows 11 version 24H2 immediately and without worry: Despite downloading a Windows 11 Insider Preview version of the 24H2 ISO, anyone upgrading to 24H2 would not need to enroll their PC in the Insider Program, and the resulting install would be fully supported and serviced normally by Microsoft in stable. That is, going forward, you would simply get the normal monthly cumulative updates, just like anyone using 23H2/22H2.

It was a great tip, but now, almost two months later, there are two caveats, one new: The ISO I mention in the tip has been superseded by newer builds and it’s not clear if they’ll work the same way. And this tip never applied to Arm64: Though Microsoft does offer a separate download page for Arm64-based Windows 11 Insider Preview ISOs, the page I linked to, which offers far more ISO download versions, does not.

Microsoft makes this needlessly complicated.

(For those on x64 who wish to upgrade to Windows 11 version 24H2, it is possible that the newer build listed on the normal Windows Insider Preview Downloads site, “Windows 11 Insider Preview (Release Preview) – Build 26100.863,” will work today. This post focuses on Windows 11 on Arm, but what I describe below should work for anyone, regardless of which platform you’re using. One day, I hope, Microsoft will just clean this up and provide all its customers with the same downloads.)

Tied to this, I’ve gotten a few questions about whether Windows 11 version 24H2 and its upgraded Prism emulator will improve the experience for existing Windows 11 on Arm PCs like those based on Qualcomm Snapdragon 8cx Gen 1, Gen 2, or Gen 3 (or their Microsoft SQ-based equivalents). This is an unknown for now because Windows 11 version 24H2 is only available publicly on newer Snapdragon X-based Copilot+ PCs. If you’re one of the hardy few still soldiering on with a previous generation Windows 11 on Arm-based PC, you’re in the same boat as the majority of x64: You’ll get 24H2 in October. But also saddled by the older x64/x86 emulator.

Assuming you wait on Microsoft, that is.

As always, there are workarounds. As always, these workarounds are a bit dicier on the Arm64 side because Microsoft doesn’t make Windows 11 on Arm ISO downloads available to the public. And so before trying what I recommend here, check with your PC maker to see whether they offer a recovery image for your PC. And regardless, use the tools built into Windows 11 (any version, including Windows 11 on Arm) to create a recovery drive where you have enabled the option “Back up the system files to the recovery drive.” I document how to do that in the Windows 11 Field Guide. That way, if anything goes south, you have a way to at least get the PC back to a stable, supported condition.

But you want to upgrade to Windows 11 version 24H2 now. And Microsoft doesn’t provide that ISO (or any other way to upgrade).

So let’s make the ISO. Or, I’ll make the ISO and you read along. It’s a bizarre thing to have to do.

A third-party website called UUP dump provides the downloads Microsoft does not, sort of. It offers a wide range of Windows 11 builds, across both x64 and Arm64, in a variety of formats.

If you click the “x64” or “Arm64” button next to “Latest Public Release build,” you can see which stable builds are available now. There are several in each case, but the most current non-preview Windows 11 version 24H2 build in stable at the time of this writing is build 26100.863. But that’s about to change, as tomorrow is Patch Tuesday. And that build, most likely, will be 26100.1000 (or some slight increment up from there), as Microsoft shipped that build in stable preview form, as June’s Week D preview update.

Not that it matters: UUP dump does not list builds 26100.863 or 26100.1000 in its Latest Public Release build offerings. Indeed, it doesn’t list any 24H2 builds, despite this version being available, sort of, in stable. So we will have to turn to its “Latest Release Preview build” view (x64, Arm64) instead. There, in each case, you will see at least one 24H2 build, but since 26100.1000 is the latest as I write this (again, check back tomorrow), we’ll go with that.

This is where things get (more) confusing.

From here, you need to select your language, edition(s), and some other options. Language is easy enough—English (United States) in my case, but there are several choices—and Windows 11 on Arm defaults to a single ISO with Home/Pro editions options by default. But on the next screen, you can customize a variety of options that collectivily determine what you get in your “download package.”

This isn’t as straightforward as downloading an ISO file, unfortunately. Instead, you will download some combination of files, including scripts (for Windows, macOS, and Linux, go figure) with which you will create a final ISO yourself. This final screen determines the makeup of those files, and there are many choices. So I will make two assumptions here: You are doing this on Windows (any version/architecture). And the goal is to create a Windows 11 version 24H2 ISO (mostly for Arm64, but this should work for x64 too).

This is how I configured the download, with the idea of upgrading a Snapdragon 8cx Gen 2-based Windows 11 on Arm PC to 24H2:

• Download method: Download and convert to ISO.
• Conversion options: Enabled “Include updates (Windows converter only)” and “Run component cleanup.”

Then, I clicked “Create download package” and downloaded the tiny (8 KB) ZIP file it gave me, which in this case was called 26100.1000_arm64_en-us_multi_653fc949_convert.zip. I extracted it to my desktop and peeked inside, finding several files.

The most important is uup_download_windows.cmd: This is the command line script you’ll run to create the ISO file. If you want to read its contents, hold down the SHIFT key, right-click it, and choose “Edit.” (You’ll need to bypass a SmartScreen warning.)

To run this file, just double-click it. You’ll get the SmartScreen warning noted above, but when you bypass that, a Command Prompt window will appear.

Type “r” (no quotes) to proceed.

This will take a while. A long while. There will be much work occurring.

But in about 30 minutes or so, depending on your PC and Internet connection, this script will build the ISO file you requested.

To find it, open the folder you had created for the extracted ZIP. It’s the big one.

If you did this on a different PC than the one you intend to upgrade, as I did, you can just copy the ISO file to a USB flash drive and then copy it to the other PC. Otherwise, just double-click it to mount the ISO as a virtual drive. Then, run setup.exe to run Windows Setup and upgrade the PC to Windows 11 version 24H2. (You can delete the folder you used to create the ISO file, just be sure to move the ISO file first.)

Assuming you’re doing the same as me—upgrading from Windows 11 version 23H2 to 24H2—then you’ll just go with the defaults and upgrade. But you could optionally do a clean install, too, of course.

Anyway, if all goes well, you’ll eventually reboot at least twice and then be prompted to sign-in normally. And when you do, you will be on Windows 11 version 24H2, and will move forward with the normal monthly servicing update in stable. (In fact, be sure to check Windows Update.)

Of course, doing this on an older Snapdragon 8cx/SQ-based PC is an interesting reminder of how slow everything was before Snapdragon X: Installing this upgrade was like watching paint dry.

At least it works. But since this process requires a third-party website and download, not to mention a SmartScreen bypass, you’re correct to be at least somewhat suspicious. I’ve been using UUP dump for years, and it’s always worked out fine—well, when it works, some builds can get scrambled—but this isn’t something I would recommend to non-technical people. And it’s certainly not something that I’d write up as a tip or add to the Windows 11 Field Guide.

But that’s the point: All Microsoft needs to do is make the Windows 11 on Arm ISOs available normally to the public, as it does with the x64 ISOs for Windows 11. This isn’t rocket science, but with Microsoft and Windows, it’s always confusing. And never as simple as it should be.

Someday, perhaps.  But this is what we have to deal with now, and this is just one of several reasons why Windows 11 on Arm is still an iffy proposition for mainstream, non-technical users. It shouldn’t be like this.