Sometimes it’s my throwaway remarks that return to haunt me most. Earlier this week, after Apple had announced that it would release macOS 14 Sonoma on 26 September, I ended my discussion of the snags and merits of upgrading early with remarks about how Sonoma would be delivered. As your comments indicated, that left many blank faces wondering what I was writing about. Let me explain, and point out the dangers of what is likely to happen in little more than a week.

Each new major version of macOS, like Mojave, comes with new firmware, a new kernel and its hundreds of kernel extensions, and pretty well everything that makes up the system. In recent years, many have brought deeper architectural changes, like the APFS file system in High Sierra, and the boot volume group in Catalina.

Moving between minor versions of macOS, perhaps from 10.14.2 to 10.14.3, was delivered as an update, an Installer package containing all the changed files brought with the new minor version. But to move between major versions, Apple supplied a self-contained app, named something like Install macOS Mojave, that was typical of an upgrade.

There was a lot of flexibility in updating macOS, with several options. You could leave it to Software Update to deliver the type of update your Mac needed, or you could download a standalone installer. The latter came in three main sizes:

• the full installer app, taking any supported Mac from a different major or minor version to a single destination, such as 10.14.3;
• a ‘delta’ update, taking macOS up a single minor version or patch, for example from 10.14.2 to 10.14.3;
• a ‘combo’ update, taking macOS up from any previous minor release of the same major version, for example from 10.14.x to 10.14.3.

For those using Software Update, the most noticeable difference between an upgrade from 10.13 to 10.14 was that it delivered a self-contained app, that was automatically started, but the user could quit if they had second thoughts, or had downloaded it in error.

Since Big Sur, this has changed. Not only are there no standalone installers any more, but even minor updates are managed quite differently. This is because of the boot volume group and the way that the Signed System Volume has to be constructed: that’s too big a job for an ordinary installer package, so even updates now come with their own installation tools built into a software update ‘brain’. This is even more complicated for Apple silicon Macs, whose firmware is different, and can’t be updated the way that EFI firmware has been in the past.

But for Big Sur and Monterey, upgrades from previous major versions of macOS were still performed by full installer apps. When Software Update downloaded the upgrade to take your Mac from Big Sur to Monterey, you got an app Install macOS Monterey. If you were given the option by Software Update of updating Big Sur to 11.6.1 or upgrading to Monterey 12.0.1 and unintentionally clicked on the upgrade rather than the Big Sur security update, then the simple way out was to quit the Install macOS Monterey app and try again to get the security update.

Apple changed this with the release of Ventura on 24 October last year. Instead of 13.0 being delivered as an upgrade installer app, it came as if it was just an update. If you had intended updating Monterey to 12.6.1, but clicked on the wrong choice and went for 13.0 instead, there was no way out: Software Update went ahead and dragged you screaming and kicking to Ventura instead.

The benefit of this new method of installing major macOS upgrades is its efficiency and speed. Instead of having to wait for a 12 GB full installer app to download, and go through the process of installing the whole of Ventura from scratch, the update was little more than 6 GB, and installed far quicker.

Only Apple knows whether the Sonoma upgrade on 26 September will use the same update mechanism as Ventura, and (as with Ventura) it doesn’t appear to want to caution us beforehand. So if you plan to update either Monterey to 12.7 or Ventura to 13.6, rather than going the whole way to Sonoma 14.0, be particularly careful when your Mac is offered the updates. If you want a security update, click on the text to show the other available updates and read them carefully before picking which to install, bearing in mind that, once you have started any of them, backing out won’t be easy.

This also applies to those using SilentKnight: on and after 26 September, when it lists available updates, they are likely to contain Sonoma. If you click on the Install All Updates button, then you’re going to get Sonoma as well. Instead, perform macOS updates through Software Update settings before attempting any updates using SilentKnight, and use the Install Named Update… command in the File menu to download and install any security data updates that might be available. Last year many ended up involuntarily upgrading to Ventura, when all they had intended was to install an update.

Of course, one way to address this would be with a confirmation dialog, reading Are you really sure you want to upgrade to Sonoma? I have the feeling though that would come with but a single button.