upgrading multiple Macs with one download

You can create a bootable macOS USB installer using the instructions in the following Apple article:

Create a bootable installer for macOS - Apple Support

If this is for a 2018-2020 Intel Mac with T2 security chip, then you will first need to boot into Recovery Mode to modify the security settings to allow booting from USB by using the Startup Security Utility.

FYI, it is usually best to provide the exact model of the Mac(s) involved since that can make a difference on how contributors answer the question. You can get the exact model & current version of macOS by clicking the Apple menu & selecting "About This Mac".

Much like many of the previous good suggestions

When you run the installer it does require and active and functional Internet connection

" The installer needs a stable internet connection to get firmware and other information specific to your Mac. "

You can download a full installer of Sequoia or any previous system with the free app  MDS V4.4. The size of the installer is 15.31 GB.

Be sure to get V4.4 of MDS as the newer versions require purchase. V4.4 works with Ventura and Sequoia. Didn't test it with Sequoia but it should work.

Following Peter Jorgensen's advice will help, but not completely eliminate the bandwidth.

When you download a new macOS, the installer is not the complete "Full" installer. It downloads a lot of content from the internet.

Once you have installed the OS, you can download the full installer. That doesn't help, though.

You can download the full installer using Terminal.

This command will list the available full installers compatible with your Mac.

softwareupdate --list-full-installers

To download the full installer, use this command, substituting the version number you want to download:

softwareupdate --fetch-full-installer --full-installer-version 15.3.2

It will download that full installer and save it in your Applications folder. You can then transfer that to your other Mac.

Peter Jorgensen wrote:

Once you download the upgrader from the App Store don't run it before storing a copy in a "safe" place like on an external drive. It is automatically deleted after running. Although the upgrader is 12.12 GB you need to have 19.78 GB free or the download won't start.

I would go even further and suggest placing the installer app into a folder such as "Sonoma Installer", then use Disk Utility to create a read-only DMG archive. I have encountered issues where trying to download the installer again will end up modifying the existing installer even if it is no longer located in the Applications folder (I discovered this the hard way). While I would hope it would not modify the file relocated to an external drive, I find it is best to place the installer into an archive file.

Peter Jorgensen wrote:

I'd like to upgrade two MacBook Airs without having to download the upgrade twice.

Download it to one of your MBAirs. The installer will be saved to your /Applications folder. (If it starts automatically after downloading, just exit the installer to stop it from running.)

Copy the installer file to the /Applications folder on the second MBAir. You can copy it via your local network or just use a flash drive.

Old Toad wrote:

You can download a full installer of Sequoia or any previous system with the free app  MDS V4.4. The size of the installer is 15.31 GB.

Your link takes you to the MDS home page, where you can buy MDS starting at $300.

MDS is up to v6 now and there is no obvious download page where one could find V4.4. By googling I was able to find a Version History page but there is no v4.4 there ... it has V4.3 (Monterey compatible) then skips to v5.0 (Sonoma), then 5.1 & v6.

The site has changed since I downloaded 4.4. There was a link to older versions. Sorry about that. I noticed that they had a trial version. Since I had already used up my trial time I couldn't run it to see if it would work. You might try it.

If you can go to the App Store and find the system you want it should download without installing.