Download macOS Beta Installer

When you log into the Apple Developer portal, you can easily download a restore image (ipsw file) for beta versions of macOS, but it’s not helpful if you want to install macOS on a separate volume on your existing Mac.

The actual macOS installer is much more useful. The only issue is that it’s not exactly intuitive to download.

Here’s how to do it:

Step 1: Turn on Beta Updates

Open the Settings app on your mac
Click General
Click Software Update
Turn on Beta Updates for macOS Sequoia

Step 2: Use Terminal to download the installer

Open a terminal window
Run softwareupdate --download --fetch-full-installer --full-installer-version 15.0

When you run that command, you’ll see a message in the console:

Scanning for 15.0 installer

If you skipped Step 1 and didn’t already opt in to receiving beta updates from Apple, you may get an error message:

Install failed with error: Update not found

If you’ve got Beta updates turned on though, you should see the softwareupdate utility begin to download the installer.

Don’t worry if you see the words “Installing xx%”. It’s not actually going to update your primary operating system. It’s actually just downloading the installer to your Applications folder.

Step 3: Find the installer in your Applications folder

Open Finder and navigate to your Applications folder
You should be able to find the Install macOS 15 beta application if the download was successful

Once you’ve got the installer, you can install macOS on a separate volume on the same Mac that you’re running the currently-released version of macOS!