How to prevent macOS 15.7 from upgrading to macOS 26? Only with a configuration profile or are there other methods available?

Have put both parts of your query to an AI / LMM

Below is what it says

I take no credit for this and proceed with some caution 

Configuration Profile 

This is the most reliable and Apple-supported method in enterprise environments.

Delay Major Updates via Configuration Profile:

You can install a mobileconfig profile that delays major OS upgrades for up to 90 days.

You can create this using Apple Configurator 2 or an MDM (Jamf, Intune, etc.).

It only delays the upgrade, not blocks it indefinitely.

Block with a Custom MDM Policy (Enterprise)

If you're using MDM, you can use restrictions to:

• Prevent users from seeing OS upgrades in System Settings > General > Software Update.
• Or prevent installation of specific builds (if using advanced tools like Jamf Pro with smart groups).

Note: MDM can’t block upgrades forever but can delay and control visibility.

All that is needed is to turn off Automatic Updates in Settings. I have several Mac's that I updated to MacOS 15.7 and they do not update to MacOS 26. I also manually updated them to MacOS 15.7.1, and they do not update to Mac OS 26 unless I choose to update them. The option is there in Settings if I ever want to update, but they have not updated automatically with that setting turned off.

My settings are exactly as what is shown by Old Toad.

It should not upgrade on its own. You can turn off auto updates in System Settings, anyway, but from Sequoia to Tahoe it’s an upgrade and I have never seen that happen without user intervention.

Servant of Cats wrote:

There are a number of Intel-based Macs that can run Sequoia, but that cannot upgrade to Tahoe. (Only four models of Intel-based Macs are eligible to run Tahoe.)

If you set aside a number of those Macs, you could be reasonably certain that nobody would be accidentally installing Tahoe on them. However, if you were talking about something like a 2018 Mac mini or 2019 iMac, it might not be reasonable to expect the system to remain in production use for another 10 years - especially as during most of that time, Apple would consider them "obsolete" for parts & hardware repair purposes.

Good points

You may also point out that once Apple Releases macOS 27 next year

Intel Computers will no longer Qualify for anything newer that what they are currently using

About the Rosetta translation environment | Apple Developer Documentation

lowlevelmission wrote:

Thank you.

We need a secure method to block upgrades forever on these macOS 15.7 devices.

The reason is that we use a lot of “FireWire devices” even measurement equipment which will still be in use for the next 5 to 10 years. Switching to other technologies is not possible.

We are very aware of the reasons for this request re " FireWire devices " and " block upgrades forever "

To be reasonable.

It appears we can not provide a Permanent solution

Technology moves on and perhaps it is time to also move on with it

There are a number of Intel-based Macs that can run Sequoia, but that cannot upgrade to Tahoe. (Only four models of Intel-based Macs are eligible to run Tahoe.)

If you set aside a number of those Macs, you could be reasonably certain that nobody would be accidentally installing Tahoe on them. However, if you were talking about something like a 2018 Mac mini or 2019 iMac, it might not be reasonable to expect the system to remain in production use for another 10 years - especially as during most of that time, Apple would consider them "obsolete" for parts & hardware repair purposes.

I setup my iPhone and Mac Mini as follows so that I don't have any automatic updates except for security and sam version fixes but no updates!