Apple - How can I download the macOS Big Sur installer on a Mac which is already running Big Sur?

You can download the official macOS Big Sur installer from Apple by using the following steps:

1. On your Mac, open the Mac App Store app, search for Big Sur and click on the Big Sur app to access the macOS Big Sur app page.

   You can also use this link to directly access the macOS Big Sur app on the Mac Appe Store:

   • https://apps.apple.com/app/macos-big-sur/id1526878132

   If the App Store app doesn't launch automatically, you can click on the View in Mac App Store button on the above webpage.

   

2. Click on the GET button.

   

3. Clicking the GET button would automatically open the Software Update preference pane under System Preferences app.

4. Click on the Download button to download the macOS Big Sur installer.

   

5. The Software Update preference pane would start downloading the installer. You can view the download progress here. If you wish to cancel the download, you can do so by clicking on the circular button with a cross shown just ahead of the progress bar.

   

6. One the installer is downloaded, the same can be found under the /Applications folder with the name Install macOS Big Sur.app.

How can I download the macOS Big Sur installer on a Mac which is already running Big Sur?

I'm finding that since this Mac is already upgraded, I can't download it again. How can I get ahold of the installer file?

Using a clean install of macOS Big Sur and then attempting to download the macOS Big Sur installer on the running occurrence of it, I was unable to do it using the methods described in the answers by bmike and Nimesh Neema in this thread.

I then tried using Terminal and the softwareupdate command:

sudo softwareupdate -d --fetch-full-installer --full-installer-version 11.0.1

I got the same "Update not found" error message as with the other methods.

What I tried next was to use the third-party python script that downloads the various packages directly from Apple's servers and assembles them into the installer app.

Note that I did not completely download it as I already have the installer and no need for the to download it again at this point, however the fact that is was downloading the packages, including the biggest one which was 11.3G in size, I'll assume the script will finish correctly as this script has been available on the Internet and in use for some time now and ifs still being maintained.

Using the installinstallmacos.py python script from GitHub:

• https://github.com/grahampugh/macadmin-scripts

In Terminal I change directory to where I download the extracted macadmin-scripts-main.zip and executed is as:

macadmin-scripts-main % sudo ./installinstallmacos.py

A bunch of stuff scrolled on the screen to stop at:

 #      ProductID    Version    Build   Post Date  Title
 1      001-15219    10.15.5  19F2200  2020-06-15  macOS Catalina
 2      001-68446    10.15.7    19H15  2020-11-11  macOS Catalina
 3      001-04366    10.15.4  19E2269  2020-05-04  macOS Catalina
 4      061-86291    10.15.3  19D2064  2020-03-23  macOS Catalina
 5      041-91758    10.13.6    17G66  2019-10-19  macOS High Sierra
 6      001-57224    10.15.7     19H4  2020-10-27  macOS Catalina
 7      061-26589    10.14.6   18G103  2019-10-14  macOS Mojave
 8      001-51042    10.15.7     19H2  2020-09-24  macOS Catalina
 9      001-36735    10.15.6  19G2006  2020-08-06  macOS Catalina
10      001-83532     11.0.1    20B50  2020-11-19  macOS Big Sur
11      041-88800    10.14.4  18E2034  2019-10-23  macOS Mojave
12      041-90855    10.13.5   17F66a  2019-10-23  Install macOS High Sierra Beta
13      061-26578    10.14.5  18F2059  2019-10-14  macOS Mojave
14      001-36801    10.15.6  19G2021  2020-08-12  macOS Catalina

Choose a product to download (1-14): 10

I chose 10 and it proceed to download the packages directly from Apple's servers.

While in Terminal you will see exactly what it's downloading and see it's coming directly from Apple's servers.

Assuming it's going to create the /Applications/Install macOS Big Sur.app application bundle, you would then use the following command in Terminal to create the installer:

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

Changing MyVolume in the command to the actual name of the volume of your USB drive been used for the installer.

See How to create a bootable installer for macOS for additional details.