Although there was no ambiguity in Apple’s announcement that later this year it will be releasing macOS 26 Tahoe, together with version 26 of its other operating systems, there have been claims that this might just be a ‘marketing version’ and not really the case. There is some evidence that could be misinterpreted as confirming that, where some of Apple’s developer web pages refer to macOS 16.

But others choose to differ.

Cast your mind back five years to macOS 11 Big Sur, when what had been expected to be macOS 10.16 but was announced as 11.0 instead. That had the potential to upset a lot of code and scripts that had become used to checking the minor but not major version number. Apple foresaw those problems, and devised an ingenious scheme that allowed Big Sur to be simultaneously both 10.16 and 11.0. It’s hardly surprising that has been implemented once again for Tahoe.

Rules

There are two fundamental rules provided by Apple:

• In compiled languages, the version returned by macOS depends on the SDK which the software has been built against. When built against the 15 SDK or earlier, Tahoe returns 16 for compatibility with previous numbering and all existing apps; when built against the 26.0 SDK, it returns 26.0 for forward compatibility.
• In scripted languages run within a shell environment, there’s an environmental variable to control the version number given. Set SYSTEM_VERSION_COMPAT=1 and Tahoe returns 16; leave that variable unset, or SYSTEM_VERSION_COMPAT=0, and it returns 26.

AppleScript

Move a script across to Tahoe, and it will be compiled in the 26 environment, so
system version of (system info)
returns 26.0, as will that code inside an AppleScript app built on Tahoe.

Scripts and other languages

One method commonly used to look up the macOS version number is to obtain the string value for the ProductVersion key in /System/Library/CoreServices/SystemVersion.plist. However, depending on the environment of the caller, Tahoe plays tricks with that file, which should return a version of 26.0. If the caller has set SYSTEM_VERSION_COMPAT=1, then the version number returned isn’t obtained from that property list at all, but its companion SystemVersionCompat.plist, which is 16.0.

You can test this at the command line, by entering the two commands
SYSTEM_VERSION_COMPAT=1 cat /System/Library/CoreServices/SystemVersion.plist
and
SYSTEM_VERSION_COMPAT=0 cat /System/Library/CoreServices/SystemVersion.plist

Which is it – 16 or 26?

macOS Tahoe is very definitely, and not just for marketing purposes, macOS 26, but depending on how you ask that question, it could pretend to be 16 if you wish.

As expected, Apple announced the next major version of macOS and its other operating systems, on the opening day of WWDC yesterday. This followed a disarming vision of Craig Federighi sporting a forest of grey hair and racing a Formula 1 car around the roof of Apple Park. Mercifully, that turned out to be a promotion for a new Apple TV+ production titled F1, rather than anything about to happen to macOS. And he didn’t crash.

Previews of each new OS were prefaced by the promise of “big announcements for all of our platforms”, and inevitably opened with plans for Apple Intelligence and Private Cloud Compute. Language support is going to be further extended, and additional new features are going to be announced later during this cycle. Perhaps most important is the news that third-party developers are to be given access to on-device Large Language Models (LLMs) through a Foundation Models Framework. This looks highly accessible, and it will be exciting to see what that enables.

As widely forecast, these new major versions bring a redesign intended to harness the power of Apple silicon, with a look dubbed Liquid Glass. This features layers of translucent controls that adapt to your actions, for example moving out of the way when scrolling. Although this is harmonised across devices, fears that macOS will be ‘dumbed down’ to resemble iOS appear unfounded. Indeed, iPadOS is steadily moving closer to macOS with a more Finder-like Files app, and iPads will at last be able to run background tasks.

Some features of Liquid Glass appear visually stunning, for example when providing 3D effects of depth in lock screen photos. Overall, from the little that has been shown so far, it looks impressive without being obtrusive or irritating. To get the best out of Liquid Glass, apps will need to be rebuilt against the improved API, and their appearance tuned lightly. Some special visual effects may need access to new API features, though.

To get the best out of this new look, icons need to be layered, and adapted for new appearance options including transparent. Apple has provided a new Icon Composer app to support that. Although I doubt whether it will become as popular as ResEdit was in Classic Mac OS, I can see Icon Composer being used more widely than the rest of Xcode.

Hardware support

Surprisingly, four Intel models continue to be supported by Tahoe. The full list given by Apple reads:

• MacBook Pro 16-inch 2019, and 13-inch 2020 with four Thunderbolt ports,
• iMac 2020,
• Mac Pro 2019,
• all Apple silicon models from 2020 onwards.

Although those Intel models will be able to use many of the new features in Tahoe, they continue to be unable to access any Apple Intelligence.

This means that Tahoe will continue to be a large Universal binary, and could in theory be supported by OCLP, although that’s likely to be more challenging. Apple has stated explicitly that Tahoe will be the last major version of macOS to support Intel Macs.

Version numbering

As rumoured, Apple has changed the numbering of all its OSes, bringing them in synchrony to version 26. This even applies to the new beta-release of Xcode for Tahoe.

Although that might come as a surprise to some code and scripts, because it’s a higher major version number than Sequoia this should present far fewer problems than did macOS 11 Big Sur. You might still like to check anything of yours that does check version numbers to ensure it doesn’t trip up.

Details

In keeping with the redesign, improvements in folder and icon appearance were mentioned early. Easy folder customisation is coming, allowing the standard icon to be enhanced with the superimposition of symbols and emoji, and its colour changed. Icons can be tinted by the user, as well as being layered in Icon Composer.

Continuity features that integrate Macs with devices are being extended with support for Live Activities added to macOS. The Phone app will be added as well, in its improved form from iOS 26.

Shortcuts gains ‘intelligent’ actions, and will have direct access to LLMs in Private Cloud Compute. Spotlight has undergone a major update, but in Global Spotlight features rather than local search. From the Spotlight icon, there will be intelligent actions integrated with Shortcuts, quick keys abbreviations, and it will be contextually aware. To take advantage of these, third-party apps will need to use App Intents.

Games will be integrated into a new Games app, and gain translucent controls.

The powerful GPUs in Macs supported by Tahoe should also become more capable, with the introduction of Metal 4.

Finally, Tahoe is dropping full first run security checks on notarized apps, which should ensure they all launch blazingly fast. Although a few malicious apps have been inadvertently notarized in the past, running XProtect checks on them seem pointless, as the notarization process involves more extensive checks than those performed by XProtect. If malware has managed to sneak past Apple’s checks and become notarized, then nothing in macOS is going to detect it as being malicious.

Release dates

Apple has already released the first developer beta-test version of Tahoe and its sister OSes. The first public beta is promised for July, and full release of macOS 26.0 is due in the fall/autumn.

I’ve already started testing my own apps.