26.4 beta and RC versions are unable to be created on anything but 26.4 beta host OS

AFAIK there’s no magic here. And I tried reproducing this on my main work Mac and didn’t have a problem. Specifically:

1. On macOS 26.3.1, I downloaded the current 26.4rc seed (UniversalMac_26.4_25E243_Restore.ipsw).
2. Using an off-the-shelf Virtualization framework app [1], I created a VM from that.
3. It installed and booted, and I was able to run all the way through MacBuddy and get to the Finder.

I’m not sure why this is failing in your environment.

This Mac is production hardware that’s only ever run released system software (plus various Xcode beta seeds).

When I wrote the above I hadn’t yet installed Xcode 26.4rc. So I installed that and repeated the test. It didn’t change anything. Things continued to work.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

[1] VirtualBuddy 2.1.

This is what I see on a brand new M5 with 26 Mobile Device Support installed + using Virtualbuddy.

I'm not entirely sure why your environment works actually.

I'm also encountering this trying to make a 26.4 RC VM on a macOS 15.7.4 (24G517) host (a M3 MBP) (FB22286320).

I have a VM working from a previous 26.4 beta that was originally on an earlier version of 26, but I wasn't able to upgrade it to the RC via Software Update due to storage constraints :( maybe it would work to make a VM with an earlier macOS version then update it? I haven't found time to test whether that works, though.

AFAIK there’s no magic here. And I tried reproducing this on my main work Mac and didn’t have a problem.

@DTS Engineer When I have this issue, it also comes with a prompt that appears offering to download the device support files, but this fails because the files aren't available from the software update server. Given that you're an Apple employee, is it possible that your work Mac has access to an internal software update server that offers the required device support files, but that the public software update server doesn't?

FB22286320

Thanks for filing that.

is it possible that your work Mac has access to an internal software update server … ?

It’s certainly possible, but I usually keep a tight reign on this Mac to prevent that sort of thing.

Anyway, based on the fact that multiple folks on this thread are reporting this issue, I think it warrants investigation by the Virtualization team. If you’re hitting this, please file a bug with the details and then post the bug number here.

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

FB22313446

FB22313446

Thanks.

I’ve been discussing this with the Virtualization team and I think I know what’s going on here. But, just to confirm, on a Mac that’s showing this problem, what does this command report:

% pkgutil --pkg-info-plist com.apple.pkg.MobileDevice
…
<plist version="1.0">
<dict>
    …
    <key>pkg-version</key>
    <string>4.0.0.0.1.1772003596</string>
    …
</dict>
</plist>

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

On my macOS 15.7.4 machine:

$ pkgutil --pkg-info-plist com.apple.pkg.MobileDevice
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>groups</key>
	<array>
		<string>com.apple.findsystemfiles</string>
	</array>
	<key>install-location</key>
	<string>Library/Apple/</string>
	<key>install-time</key>
	<integer>1771452321</integer>
	<key>pkg-version</key>
	<string>4.0.0.0.1.1762585687</string>
	<key>pkgid</key>
	<string>com.apple.pkg.MobileDevice</string>
	<key>receipt-plist-version</key>
	<real>1</real>
	<key>volume</key>
	<string>/</string>
</dict>
</plist>

maybe it would work to make a VM with an earlier macOS version then update it?

Regarding this idea, my storage issues cleared up with the final release of macOS 26.4 (the new update required about ~5 GB of VM in my pre-existing VM, but the RC wanted about ~35 GB for some reason).

I was able to update the VM and run it. So, it does seem like a possible workaround is to install a VM with an older version of macOS and then use Software Update inside the VM to update it to 26.4.

❯ pkgutil --pkg-info-plist com.apple.pkg.MobileDevice
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>groups</key>
	<array>
		<string>com.apple.findsystemfiles</string>
	</array>
	<key>install-location</key>
	<string>Library/Apple/</string>
	<key>install-time</key>
	<integer>1772135996</integer>
	<key>pkg-version</key>
	<string>4.0.0.0.1.1762585687</string>
	<key>pkgid</key>
	<string>com.apple.pkg.MobileDevice</string>
	<key>receipt-plist-version</key>
	<real>1</real>
	<key>volume</key>
	<string>/</string>
</dict>
</plist>

I can't reply in the thread above as a comment due to limited text amount.

OK, here’s a summary, sorted by version:

Version              | User
-------              | ----
4.0.0.0.1.1762585687 | kthchew
4.0.0.0.1.1762585687 | nathan-pierce-veertu
4.0.0.0.1.1772003596 | eskimo

As you can see, I’m on the latest. And this is indeed the version of the MobileDevice package inside Xcode 26.4 [1]. Consider:

% plutil -extract CFBundleShortVersionString raw /Applications/Xcode.app/Contents/Info.plist   
26.4
% xar -xf /Applications/Xcode.app/Contents/Resources/Packages/MobileDevice.pkg
% cat PackageInfo 
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<pkg-info … version="4.0.0.0.1.1772003596">
    …
</pkg-info>

Earlier I wrote:

When I wrote the above I hadn’t yet installed Xcode 26.4rc. So I installed that and repeated the test.

I don’t think that had an effect because I’d installed an earlier release of the Xcode 26.4 beta, one that had the same MobileDevice installer version. So I was on the latest MobileDevice prior to running my test, and updating to Xcode 26.4rc didn’t change that.

So my understanding of how this should work is that:

• During the beta cycle, developers can get the required MobileDevice by installing the latest Xcode seed.
• Once the OS is released, either:
  • The user’s host will have the necessary Mobile Device
  • Or they’ll be prompted to install it

AFAICT there’s no info on that thread to contradict this. But if I’ve missed something, please let me know.

I can't reply in the thread above as a comment due to limited text amount.

It’s better to reply as a reply anyway; see Quinn’s Top Ten DevForums Tips for this and other titbits.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

[1] I’m not using the released version of Xcode 26.4, but I got the same results when I ran this test yesterday with Xcode 26.4rc.

During the beta cycle, developers can get the required MobileDevice by installing the latest Xcode seed.

That's problematic on macOS 15.x because Xcode 26.4 now requires macOS 26.2. However, would it be possible to open the Xcode.app/Contents/Resources/Packages/MobileDevice.pkg manually on a macOS 15.x machine to get the required mobile device files?

Once the OS is released, either:

That doesn't seem to match my experience. macOS 26.4 is now out, and I've updated to macOS 15.7.5 (24G624), but when I try using the restore image of the release version of macOS 26.4 to make a VM, I'm still prompted to install the mobile device files and it still says that they aren't available from the software update server.

I extracted the MobileDevice.pkg from 26.4 Xcode and installed it on 15.x. I can now create a VM for the 26.4 release.

Little request for the devs at apple: Please make these MobileDevice pkgs available on the downloads site for every release. I shouldn't need to download the whole Xcode.app and extract it manually each time I need this pkg. <3

Weirdly I had to install it twice on one older M1. I did it first with sudo installer -pkg MobileDevice-26.4.pkg -tgt / and then had to use the GUI to install. Just FYI for anyone who has the same issue