Apple has released macOS Sequoia 15.8.1 Release Candidate 2 for developers, carrying build 24H212. The September 21, 2026 update is a second near-final candidate for Macs remaining on the Sequoia branch rather than moving to a newer major release.
Apple’s macOS release-notes library remains the official place for developer changes and known issues. It does not currently provide a change list for macOS 15.8.1 RC 2, so Apple has not published specific fixes that can be assigned to build 24H212.
The RC label means the build is a candidate for public release, not a finished update guaranteed to ship unchanged. Apple may promote it if testing succeeds or replace it with another candidate. There is no confirmed public-release date in the available documentation.
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No published feature or security list yet
Apple has not announced new features for macOS 15.8.1 RC 2. It has also not attached a security advisory to the prerelease build. Specific vulnerability claims should wait until Apple posts security content for a public update.
The previous Sequoia 15.8 RC testing round also arrived without a detailed consumer feature list. Our explainer on Apple’s software-support branches shows why an older macOS line can continue receiving maintenance updates after a newer version is available.
How developers can install RC 2
On an enrolled Mac, open System Settings, select General, and choose Software Update. Open Beta Updates if necessary and select the macOS Sequoia developer channel. Back up the Mac before installing, particularly if it stores production work or uses software with strict version requirements.
After the restart, testers can confirm build 24H212 from General and About. Macs kept on an older branch often run important legacy apps or managed workflows, so compatibility checks for security tools, extensions, peripherals, backups, and business software are more useful than assuming an undocumented fix.
Our macOS beta installation guide explains the enrollment controls. Users who do not need to test apps or managed deployments should wait for the public build and Apple’s final release notes.
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