Newer macOS on an Old iMac with OpenCore Legacy Patcher

If your iMac is too old to update past High Sierra, Catalina, Big Sur, Monterey or Ventura, it has reached the last macOS Apple will ever give it, and Software Update will not offer anything newer. OpenCore Legacy Patcher, a free, open-source tool, can install macOS Sequoia on iMacs from 2009 to 2017, and we do the whole job from $249 at our workshop near Castle Hill. It is unofficial and not supported by Apple, it comes with trade-offs we set out in full below, and whether to go ahead is your decision.

Why being stuck on an old macOS matters

On 14 September 2026 Apple released macOS 27 with security updates for Tahoe (26.7) and Sequoia (15.8), and nothing for Sonoma or older. So every iMac from 2009 to 2017 still on its official macOS is running a version outside Apple's regular security updates. The daily problem is apps. As of September 2026:

• Google Chrome needs macOS 13 Ventura or later. Chrome 150 was the last version for Monterey and 138 the last for Big Sur. Older copies keep running, without updates.
• Microsoft 365 and Office need macOS 14 Sonoma to receive updates, security fixes included. On older versions the apps still work but stay frozen: Monterey at 16.88, Ventura at 16.101.
• Adobe Creative Cloud 2026 apps support Sonoma, Sequoia and Tahoe only.
• Safari is tied to macOS. Monterey stays on Safari 17 and Ventura on Safari 18, and Safari 27 needs Sequoia or newer.
• Firefox needs Catalina (10.15). On macOS 10.12 to 10.14, including High Sierra, Firefox 115 ESR is the last version, with security updates until March 2027.

Australian banks list supported browsers, not macOS versions, and Westpac, for one, asks you to keep yours up to date. On High Sierra, only Firefox of those three still gets security fixes, until March 2027.

Apple has finished with Intel iMacs

At WWDC in June 2025, Apple said macOS Tahoe would be the final release for Intel Macs, and macOS 27 Golden Gate arrived on 14 September 2026 for Apple silicon only. The one Intel iMac that runs Tahoe is the 27-inch 5K from 2020; the 2019 models stop at Sequoia. Several technology sites report Apple saying Intel Macs will get security updates for three years, but we have not found that commitment in a current Apple document and Apple has published no end date, so treat it as reported, not promised.

What OpenCore Legacy Patcher is

OpenCore Legacy Patcher (OCLP) is the free, open-source project from Dortania, a group of volunteers, that lets you install Sequoia on an unsupported Mac. OpenCore runs at startup, before macOS loads, so an unsupported Mac can boot and install a newer macOS. Root patches then put back the graphics, Wi-Fi and other drivers Apple removed for older hardware.

The project's FAQ says it is designed to target macOS Big Sur 11 to macOS Sequoia 15, with no support outside that range, and release 2.5.1 (19 September 2026) does not support Tahoe. In March 2026, with several developers gone, the team said it could not commit to a Tahoe update. Unofficial forks claiming Tahoe support are not Dortania projects, and we do not install them. On a patched iMac, Sequoia is the ceiling and may stay that way.

What each iMac gets from the patcher

Choose About This Mac from the Apple menu to see your model and year. For the exact Model Identifier (for example iMac18,3), hold Option, open the Apple menu and choose System Information.

Non-Metal (2009–2011). These chips cannot run Metal, the graphics technology current macOS relies on. Sequoia runs, but Maps and what depends on it (Find My, Places in Photos) is broken, DRM video will not play, Stage Manager does not work, Zoom needs a patch, and Pages, iMovie and GarageBand need older builds.

Legacy Metal (2012–2015). Graphics acceleration works once patched, but Safari fails to play DRM video on most of these chips from Sonoma on, Live Text and face detection in Photos are off by default on 2012–2014 graphics, and on Sequoia, Nvidia models can see Software Update stall.

Processor limits. Since Ventura, more apps use the AVX and AVX2 instructions and quit with an "illegal instruction" error on processors without them. The 2009–2010 iMacs have neither, the 2011 and Late 2012 have AVX only, and Late 2013 onwards have both. On 2009–2010 models the patcher works around the missing AVX for Safari, but not for every app.

For other upgrades that suit your machine, see the 2009–2011 iMac, 27-inch 2012–2013, 21.5-inch 2012–2014, 21.5-inch 2015–2019, 27-inch 5K 2014–2017 and 27-inch 5K 2019–2020.

The risks, in plain terms

• Nobody supports it. Apple warns that system software not designed for your Mac can cause startup failures, app crashes, and display, audio, Bluetooth and Wi-Fi problems. The patcher is offered as-is by volunteers who stopped taking new donations in March 2026, and almost a year passed between versions 2.4.1 and 2.5.0.
• Security protections are lowered. System Integrity Protection has to be lowered on every unsupported Mac running Ventura or newer, and it cannot be turned back on after root patching without risking the install. Root patching also breaks the sealed system volume, and on models that need unsigned patches, Apple Mobile File Integrity is turned off.
• Patches go back on after every update. Each macOS update removes the root patches, so whatever they fixed, such as graphics acceleration or Wi-Fi, stops working until they are reinstalled, and some Sequoia installs need internet access for that.
• Automatic updates stay off. The developers strongly recommend it, downloads included, because a staged update modifies the system and can break it, even though Sequoia 15.4 and later keep asking you to switch them back on. Wait a few days after each Apple release.
• Every update is full size. With the seal broken, each update is a complete copy of macOS rather than a small one.
• No easy way back. Returning to an older macOS means erasing the drive, and some Apple point releases, such as Sequoia 15.4, have needed fixes to the patcher afterwards.
• Some features will not work. iPhone Mirroring needs a T2 chip and Apple Intelligence needs a Neural Engine, so neither can be added. Sidecar, Universal Control, AirPlay to Mac and Continuity Camera are off by default because the developers consider them a stability risk.
• The runway is short. Sequoia received 15.8 on 14 September 2026. Apple publishes no end date, but it has recently patched the current macOS and the two before it, so our reading is that Sequoia's security updates stop around September 2027. After that, a patched iMac has nowhere to go unless the patcher gains Tahoe support.

Why we fit an SSD and check the RAM first

Newer macOS asks more of old hardware, and the patcher's own FAQ admits newer versions are harder to run and can appear slower. The drive matters most. Apple's file system, APFS, was designed for SSDs, and Howard Oakley of The Eclectic Light Company notes that on a hard disk its metadata can become badly fragmented, so a boot hard disk gets slower over weeks and months. Many of these iMacs shipped with a hard drive, or a Fusion Drive with as little as 24GB or 32GB of flash. On any iMac without a full SSD, we recommend an SSD upgrade (from $599 with 500GB, data transfer and macOS setup) alongside the patcher.

The patcher needs at least 3GB of memory to install Sonoma or Sequoia, and we like to see well above that. A RAM upgrade with 16GB fitted is from $329 on 27-inch and 2009–2011 models, which have an access door, or from $449 on the 21.5-inch 2012–2013, 2017 and 2019, which need the display removed (from $249 extra alongside an SSD). The 21.5-inch Mid 2014 and Late 2015 have soldered RAM, so nothing can be added. SSD and RAM jobs are usually finished in one to two business days when parts are in stock. If speed is your only complaint, see why an iMac runs slow.

Checks you can do before you book

1. Install the last updates Software Update offers, so the firmware is current, as the patcher's developers recommend.
2. In About This Mac, check the memory and whether the startup disk is a hard drive, a Fusion Drive or an SSD.
3. Check that none of your essential apps needs Apple Intelligence, iPhone Mirroring, or AVX2 on a 2012 or older machine.
4. Make a full backup and check that you can open files from it.

Who it suits, and who should skip it

A good fit: 2017 iMacs, which need no graphics patches, 27-inch 5K models from 2014 and 2015, and 2012–2013 iMacs with an SSD, used for browsing, email, banking, Microsoft 365 and photos by someone comfortable updating by hand.

Skip it if:

• Your iMac is a stock 2009–2011 model. Too much is broken for a machine you rely on; for light use, High Sierra with Firefox 115 ESR lasts until March 2027. The developers recommend a Metal-capable graphics card for these, but that is a community modification with modified card firmware, so ask us about iMac graphics work first.
• It is a 2019, already on Sequoia, or a 2020, already on Tahoe. The patcher gives neither of them anything.
• You need Apple Intelligence, iPhone Mirroring or updates that install themselves.
• Your employer or IT provider requires a supported operating system.
• The upgrades it needs cost more than you want to spend. On a 27-inch 2012–2013, which sells privately for around $220, an SSD and the patcher together start from $848, so do it only if you want to keep that particular iMac. Our guide to repairing or replacing an old iMac does the maths.

What our service includes, from $249

• A backup check before we change anything.
• Checks of the firmware, memory and drive health, so we never install onto a failing drive.
• Creating the USB installer, usually for Sequoia, the only version in the patcher's range still getting Apple security updates.
• Installing OpenCore Legacy Patcher to the internal drive, so the iMac starts without the USB stick.
• Installing macOS.
• Applying the root patches your model needs, such as graphics and Wi-Fi.
• Turning off automatic updates, including automatic downloads.
• A post-install check of Wi-Fi, graphics acceleration, audio, and sleep and wake.

We can also show you how to reapply the patches after each macOS update. Any SSD or RAM upgrade is done in the same visit.

iMac work is drop-off only at our workshop near Castle Hill, Monday to Saturday, 8am to 6pm, for customers across the Hills District and from Parramatta, Blacktown, Penrith and the rest of Western Sydney. The phone quote is free, with no obligation. The iMac repair and upgrades hub covers our other services, and the iMac repair cost guide lists every price.

Call 0400 454 859

Questions

Can OpenCore Legacy Patcher install macOS Tahoe on my iMac?

Not the official release. Version 2.5.1, from 19 September 2026, supports Big Sur to Sequoia only. The developers say work on Tahoe continues but a release is uncertain, and in March 2026 they said they could not commit to one because several developers had left. Unofficial forks claim Tahoe support, but they are not Dortania projects and we do not install them. The only Intel iMac on Tahoe is the 2020 27-inch, officially.

Can you install Sonoma instead of Sequoia on an unsupported iMac?

Yes, the patcher supports Sonoma, but we usually advise against it. Apple released no Sonoma security update on 14 September 2026, and the last one was 14.8.9 on 6 August 2026. Sequoia still receives security fixes, so it is the better target unless an app or device you rely on only works on Sonoma. Both versions need at least 3GB of memory to install.

Will my iMac be slower on Sequoia than on its old macOS?

It can be, especially if it still has a hard drive. Newer macOS versions are heavier, and the patcher's developers admit there is not much to be done about that. Expect the first few hours after installation to be sluggish while Spotlight indexes the drive. With an SSD and enough memory, everyday work on a 2012 to 2017 model is usually fine. Without an SSD, we would not recommend it.

How do I update macOS after installing OpenCore Legacy Patcher?

Wait a few days after Apple releases an update, in case it causes problems on patched Macs. Then install it manually through Software Update and expect a full-size download. After the restart, open OpenCore Legacy Patcher and reinstall the root patches with the iMac online, because some Sequoia installs need to download support files first. For a major version upgrade, the developers recommend using a USB installer instead.

Can I undo OpenCore Legacy Patcher and go back to my old macOS?

Not without erasing the drive. The patcher's developers are clear that you cannot downgrade macOS and keep your data in place. Going back means backing up, erasing the drive, reinstalling the older macOS and then copying your files back from the backup. That is why we check your backup before we start, and why it is worth deciding carefully before going ahead.

Is a 2017 iMac worth upgrading to Sequoia?

It is the best candidate among the Intel iMacs, because its graphics need no patches. Apple's last Ventura security update came in August 2025, and Microsoft 365 updates stopped at version 16.101 on Ventura. Sequoia brings current Safari and Office updates back, with security fixes until about late 2027 on our reading of Apple's pattern. Standard 2017 models shipped with a hard drive or Fusion Drive, so plan an SSD alongside it.

What is the latest macOS for a 2015 iMac?

It depends which 2015 model you have. The 27-inch 5K from Mid 2015 shares a model identifier (iMac15,1) with the Late 2014 5K and, like it, stops at Big Sur. Every Late 2015 iMac, including the 21.5-inch, the 21.5-inch 4K and the 27-inch 5K, stops at Monterey. With OpenCore Legacy Patcher, all of them can run Sequoia using the Legacy Metal graphics patches. About This Mac shows which one you have.