The update to bring macOS Tahoe up to version 26.4 is hefty at around 7.15 GB (more than double that if you’re unlucky), and reflects a great deal of bug fixes and improvements in almost every subsystem. Apple provides three good sets of release notes:

• General release notes include the addition of an option to use compact tabs in Safari, Freeform’s new Creator Studio enhancements, and a facility for Purchase Sharing in Family Sharing. Oh, and the requisite eight new emoji.
• Enterprise release notes are extensive, but contain little for the non-enterprise user.
• Security release notes list over 70 fixes, many of which are significant, but none are reported as being known to be exploited in the wild at present.

The new build number of 26.4 is 25E246. The Darwin Kernel version is 25.4.0, and XNU 12377.101.15~1.

Apple silicon firmware is updated to a completely different version numbering system, and is now reported as mBoot version 18000.101.7. If you’re running SilentKnight older than version 2.14 (71), then it’s likely that it will crash as a result of this change in firmware version. Please use version 2.14 from here.

Looking through the bundled apps and /System/Library, there are a great many increments in build numbers reflecting the extensive changes made. Here are a few of the more substantial changes found.

In bundled apps:

• Books goes from version 8.1 to 8.4
• Freeform, version 4.3 to 4.4
• iPhone Mirroring, version 1.5 to 1.6
• Music, version 1.6.3 to 1.6.4
• Safari, version 26.3.1 (21623.2.7.111.2) in BSI (a) to 26.4 (21624.1.16.11.4)
• TV, version 1.6.3 to 1.6.4
• Audio MIDI Setup, version 3.7 to 3.8
• Digital Color Meter, version 6.10 to 6.11
• Screen Sharing, version 6.2 (758.1) to 6.1 (760.4), note the reduction in version number.

In /System/Library:

• AGX kernel extensions all have build increments
• AppleDiskImages2 kext has a build increment
• AppleEmbeddedAudio kext and its plugin kexts have build increments
• AppleIntel Graphics kexts have version increments
• AppleStorageDrivers kext and its plugin kexts have build increments
• APFS is updated from 2632.80.1 to 2811.101.1, suggesting a substantial change has been made
• new private frameworks include ASMExclaveSupport, AccelerateOpt, AlwaysOnExclavesDaemon, AnteroAgent, AppRemoteAssets, AudioPasscodeDSP, BNNSOdieDelegate, CookingData, CoreTransparency, DynamicPrefetching, InAppFeedback, NanoPassKit, PartnerVisualSearch, a whole family of Unilog frameworks, and a group of iCloudWeb frameworks
• mdimporters updated include those for Application, CoreMedia, Mail, Office, iWork but not RichText.

After seeing the new CookingData private framework, I looked out for RecipeKit, but was disappointed not to see it.

This is probably going to be the last such substantial update to macOS Tahoe, as much of Apple’s engineering effort is transferring to make macOS 27 ready for release as a beta at WWDC in early June.