Hardware: • Mac Studio (M1 Ultra) • Apple Silicon • Sufficient free disk space (~35GB+ available) • SIP enabled • 4 local Time Machine snapshots present
Current System: • Already running macOS Tahoe beta • Attempting upgrade to macOS Tahoe 26.4 Beta (Build 25E5207k)
Primary Issue: Software Update downloads successfully, then moves to “Preparing…”. It stalls at “About 5 minutes remaining” for ~10–15 minutes and fails with:
“Failed to prepare the software update. Please try again. An error occurred while downloading the selected updates.”
The error appears network-related, but download always completes.
Observed Behaviour: • “Checking for Updates” completes in <3 minutes. • softwareupdated and mobileassetd CPU usage <1%. • softwareupdate --history shows no record of the failed beta install. • No excessive system load or obvious disk pressure.
Steps Already Attempted: 1. Standard Software Update retries
• Multiple download/retry cycles from System Settings.
• Same Preparing failure every time.
2. Permissions / Disk Access
• Granted Terminal Full Disk Access.
• SIP remains enabled.
• Some system-protected locations still return “Operation not permitted”.
3. Cache / State Cleanup Attempts
• Removed /Library/Updates/*.
• Cleared temporary softwareupdate folders under /private/var/tmp.
• Attempted MobileAsset cache cleanup where permitted.
• Killed softwareupdated and mobileassetd processes (auto-restarted by launchd).
4. Beta Channel Reset
• Turned Beta Updates OFF in System Settings.
• Rebooted.
• Re-enabled Beta Updates.
• Forced catalog refresh via softwareupdate -l.
5. Snapshot Check
• tmutil listlocalsnapshots / shows only 4 snapshots (normal range).
6. Full Installer Workaround
softwareupdate --list-full-installers shows:
• macOS Tahoe Beta 26.4 (25E5207k)
• Tahoe 26.3 / 26.2 / 26.1
• Sequoia / Sonoma / Ventura / Monterey installers
Downloaded installer via: softwareupdate –fetch-full-installer –full-installer-version 26.4
Installer downloaded correctly: /Applications/Install macOS Tahoe Beta.app 7. startosinstall Method (Apple Silicon optimized) Attempted install with:
sudo “/Applications/Install macOS Tahoe Beta.app/Contents/Resources/startosinstall”
–user
–agreetolicense
–nointeraction
–forcequitapps
–rebootdelay 30
–passprompt
Authorization succeeds, installer begins preparing, but installation still ultimately fails.
Additional Notes: • CPU usage remains low during failure. • No excessive snapshot count. • Error messaging consistently references download/network even though download completes. • Issue appears to occur during cryptex/asset preparation phase rather than initial download.
Question for Apple / other developers: Has anyone else seen Tahoe 26.4 beta fail specifically during the Preparing phase on Apple Silicon (especially Ultra-class chips)? Looking for confirmation whether this is a known MobileAsset or cryptex staging issue, or if logs indicate a deeper APFS / volume-owner authorization problem.
