I just bought a brand new M4 iMac because my Macbook Pro maxes out at Ventura and TurboTax will not run on it. I was very disappointed to see that it shipped with Tahoe.
I spent a couple of hours trying to figure out how to downgrade to Sequoia until I stumbled on an article that said if the machine was bought directly from Apple with Tahoe onboard you cannot downgrade because of the firmware. Is this true or is there a way around this limitation?
Many thanks in advance.
Yes the machine will have Tahoe firmware on it. The M4 iMac originally shipped with Sequoia, so you can downgrade the OS to Sequoia which will run with Tahoe firmware.
You should be able to downgrade the firmware by putting the machine in DFC mode, connected to a second Mac.
Have you actually used Tahoe, IMO it is not as bad as the forums imply!
Indeed, one advantage of Apple Silicon Macs is that you can put whatever firmware on there you like, as long as it was at one time supported by that Mac. This is unlike Intel Macs, where firmware can only be upgraded, but not downgraded (and can go out of sync with the installed macOS version).
To do this firmware and OS downgrade, you need to get the IPSW file that contains the Sequoia macOS installer and the Sequoia firmware. You then put your new Mac in DFU mode and install from there. First the new firmware, then the OS, and then you set it up as if it were a brand new Mac that happened to ship with Sequoia.
A good spot to get the link to the Sequoia IPSW is Mr.Macintosh. Note you only get the link from there. The actual IPSW itself comes from Apple and is kosher.
The next step is going into DFU mode. You need a USB-C cable (not a TB cable!) and another Mac for that and you need to know which one of the new iMac’s USB ports if the DFU port (the rightmost port when looking from the back). All of those details you can get courtesy of Howard Oakley.
Good luck!
I agree that the safest way to install an older version of macOS on Apple Silicon is to go through the DFU procedure, but do we actually know that the current Tahoe firmware is not compatible with Sequoia installations? Has anyone tried running a 15.x full install from a bootable Sequoia installer on a Mac with Tahoe firmware?
All I know is that I had to back-out Tahoe to Sequoia on an M1 Ultra Mac Studio, because of the loss of Firewire, and it has been the worst nightmare of a regression, I have ever had. Two weeks into it, it’s still not put back together… And I haven’t gotten sh!!t done.
I would also like to know the answers to these questions. I purchased an 2025 M4 Mac Studio a few weeks ago, and it came with Tahoe.
I want to downgrade it to Sequoia, and am wondering if I can get away with just using my Sequoia installer on an external bootable drive to do so, without having to do a firmware downgrade first.
I haven’t started moving anything to the Studio yet (tax season 
), so this is a perfect time to do it — I can happily wipe the drive and start from scratch.
I doubt you would ever get a firm answer from Apple on this. But I personally would have no reservations to try to it. The worst that can happen is an unstable system in which case you can still wipe it, install Sequoia firmware, and re-install using MA to get back your data form the most recent backup.
Thank you to everyone. My understanding is, and please someone prove me wrong, that the second Mac that you need for the DFU firmware change also has to be running Sequoia. Alas, my MBP on Ventura will not suffice, correct?
Cheers, John
You should be able to use a Ventura Mac. The thing that requires Sonoma or newer is Finder support for DFU mode. But if you download Configurator 2 from Apple you can use that to connect to Macs in DFU mode and install IPSW.
One other comment:
Since newer versions of an OS have different features and capabilities than older versions of an OS, copying/migrating settings files from a newer OS to an older OS can be prone to incompatibililties.
For example, if the original poster used Apple’s Migration Assistant to move files from a Sequoia machine to the Tahoe machine, I would make a backup of any newly revised or created documents from the Tahoe machine to another disk or cloud location, then downgrade the Tahoe machine to Sequoia, then run Migration Assistant to migrate files from the old Sequoia machine to the newly “downgraded” machine, and finally restore the files that were created/modified on the Tahoe machine.
If that isn’t possible, e.g., there is no old Sequoia machine or Sequoia backup, then the original poster would be best off doing the downgrade and then manually rebuilding the system or restoring files as they are needed. Either option can be very laborious, unfortunately.
I tend to buy older refurbished Macs that come with older versions of MacOS.
I have recently dual booted Sequoia and Tahoe on the same mac. This is quite a common setup by people evaluating Tahoe. Since the machine had Tahoe installed the firmware was Tahoe and Sequoia ran quite quite happily with the Tahoe firmware.
I posted about some issues in connection with migrating from backups of the Tahoe Data volume in this thread.
My understanding is, and please someone prove me wrong, that the second Mac that you need for the DFU firmware change also has to be running Sequoia. Alas, my MBP on Ventura will not suffice, correct?
As Simon says the second machine does not need to be on Sequoia. The DFU restore process automatically downloads the appropriate firmware for the machine being restored so the OS on the restoring machine doesn’t matter. (If you want to put a different firmware on you can download it separately.)
I have done DFU restores about five times since the first silicon macs, the most recent being yesterday. Every time is an adventure! As Mr Macintosh warns, timing is critical, and it always takes me a few attempts. Yesterday what worked after a few tries was using a stopwatch to time the first 10 seconds. Latest macs can use Finder instead of Apple Configurator, but yesterday I used Configurator, after failing a few times trying to use Finder. The failed Finder attempts may have been because at that stage I was not using a Stopwatch.
Thank you, Simon.
If there is an incompatibility between Tahoe firmware and a Sequoia install, how does this incompatibility manifest itself? Is it obvious from the beginning that there’s a problem?
John
My preferred solution also except Apple didn’t have any refurbished iMacs in the configuration I wanted. I also googled numerous times what macos version new macs shipped with and the answer was always “Sequoia” but lo and behold my new machine came with Tahoe. Sad face.
Like it or not (and with certain minor exceptions) Apple’s not going to ship its machines with anything but the latest OS.
Indeed, thanks for the reminder. That scenario completely slipped my mind.
I don’t doubt that there may have been scenarios where a firmware update interfered with running a previous OS, but I suspect that case is much more of an outlier than the rule. Somehow, the notion has become very commonplace.
Migration Assistant may actually refuse. When I bought my current Mac (and M4 mini), I tried to migrate from a Time Machine backup from my prior Mac (a 2018 mini).
Migration Assistant complained that the version of macOS that made my Time Machine backup was newer than the macOS installed on the computer. It then upgraded macOS on its own before doing the migration.
If you’re going to downgrade like this, I’d only restore home directories and documents, not the rest of the system. This will take longer, since you’ll need to reinstall and configure your apps, but it won’t generate any problems resulting from internal data files being incompatible with the older system.
Hey Everyone, I did a clean erase and install of Sequoia without changing the Tahoe firmware and so far so good. It’s behaving like a real computer. The caveat is I am still just installing apps and utilities, I haven’t done any actual work yet but it’s looking good. Thank you so much for the help and suggestions. This really is a great group of people here on TidBits.
Great! It can be Done!