My Mac refuses to update to macOS Sequoia 15.7.9

macOS Sequoia 15.7.9 is a current Apple update, released August 6, 2026, so the update itself is legitimate.

Since Software Update is specifically telling you to contact Apple Support and it has failed twice, I’d first restart the Mac and try Software Update again from System Settings > General > Software Update.

If it fails again, note the exact wording or any error code you get. That would help narrow down whether this is a download, installation, or verification problem. Apple also has troubleshooting steps for errors during a macOS update.

macOS Sequoia 15.7.9 was released August 6, 2026, and Apple currently lists the 24-inch M1 (2021) and later iMacs as compatible with Tahoe 26. (Apple Support)

Troubleshooting the macOS Sequoia 15.7.9 update

Since your 24-inch iMac is running macOS Sequoia 15.7 and is also eligible for macOS Tahoe 26, 

I would first determine whether the Mac's Software Update system is actually seeing Sequoia 15.7.9 rather than immediately trying more extensive troubleshooting. 

Apple confirms that Sequoia 15.7.9 is a legitimate security update released on August 6, 2026. (Apple Support)

Open Applications >> Utilities >> Terminal and enter:

softwareupdate --list

Then paste the complete output here. 

We are particularly interested in whether macOS Sequoia 15.7.9 appears in the list. 

If it does, that tells us the Software Update system is detecting the update; if it does not, that gives us a different situation to investigate.

If macOS Tahoe 26 appears instead, that will also be useful information.

For now, I would not use Terminal to install anything, such as softwareupdate --install --all. 

Let us first see what the Mac reports.

If 15.7.9 is listed but the normal Software Update process still fails, the next useful information will be the exact wording of the failure message. 

We can then decide whether to investigate storage, the network connection, Safe Mode, or another possibility. 

I would not erase the Mac or reinstall macOS at this stage.

Apple's documentation confirms that the 24-inch M1 iMac and subsequent 24-inch iMac models are compatible with Tahoe 26. (Apple Support)

Useful Apple references are About the security content of macOS Sequoia 15.7.9, macOS Tahoe 26 compatibility, and Identify your iMac model.

The key point is that we are ‘not yet trying to fix anything—we are establishing what Apple's Software Update mechanism actually sees. 

That should give us a much firmer basis for the next step.

Pls. tell us the exact model iMac you have. It will be something like "iMac 4K 2019" or "iMac 5K 2020" or similar. (Do Apple > About this Mac to get the information.) This will help us begin to identify the problem.

In my experience Macs have not been "prompting" to update Sequoia for almost a year now. They "prompt" to upgrade to Tahoe. Maybe a red dot on the System Settings app icon to indicate an update is available but no actual prompt.

corbinbdc wrote:

It's an M4, currently running Sequoia 15.7.3, -- twice letting me know 15.7.9 is available, then whey I try to download it says "contact Apple support." Makes no sense. I do not WANT to upgrade to Tahoe, I've heard bad things about it.

Your situation is fairly straightforward: your M4 iMac is running macOS Sequoia 15.7.3, Software Update is offering Sequoia 15.7.9, but the installation fails and tells you to contact Apple Support.

Apple does list macOS Sequoia 15.7.9 as an official Sequoia update, so there is no reason to assume that you need to move to Tahoe in order to update your Mac. Apple’s macOS Sequoia security updates

At this point, however, the information you have provided doesn't establish why the update is failing. 

Apple says that update failures can have several possible causes and recommends checking the internet connection and available storage, and, if the problem persists, trying the installation in Safe Mode or through macOS Recovery. Apple: If an error occurred while updating or installing macOS

Since your Mac has Apple silicon, you can enter Safe Mode by shutting it down, holding the power button until “Loading startup options” appears, selecting your startup volume, holding Shift, and choosing Continue in Safe Mode. Apple then recommends trying the installation again.

I would start with Safe Mode rather than making more substantial changes to the system. If 15.7.9 still refuses to install, Apple's next troubleshooting option is macOS Recovery.

So, for now, I would stay with Sequoia and troubleshoot the 15.7.9 installation failure, rather than assuming that upgrading to Tahoe is necessary.

corbinbdc wrote:

I restarted my Mac and now 15.7.9 is apparently downloading (it wouldn't let me do that before) - all 4.89G of it. Though I don't know why -- I've never had to restart my computer before downloading an update. We'll see if it installs it once downloaded. Thanks.

I am pleased to hear that the download is finally completing. 

Occasionally, a restart can resolve any issues preventing the update from starting, even though this should not be necessary.

I hope that version 15.7.9 will install successfully once the download is complete.

Should  there be another Sequoia will be offered in the near future .

You may consider restarting your computer before attempting another update. 

🦉-53 and you are welcome

corbinbdc wrote:

I restarted my Mac and now 15.7.9 is apparently downloading (it wouldn't let me do that before) - all 4.89G of it. Though I don't know why -- I've never had to restart my computer before downloading an update. We'll see if it installs it once downloaded. Thanks.

A restart is not required in order to start a download, so there must have been something going on in your Mac that was interfering with the download. Restarting cleared up whatever that was.

Unexplained gremlins can & do show up from time to time ... in the most unexpected places and with no explanation ... a restart from time to time is good operating practice.

for your issue—

You can download the full Sequoia installer 15.7.9 using the Terminal.app copy and paste:

sudo softwareupdate --fetch-full-installer --full-installer-version 15.7.9

your psswd will not register/show on the screen enter it anyway, then use the enter\return key to proceed. Let it run until it completes.

My Mac refuse to give macOS Tahoe