@@ -32,14 +32,8 @@ jobs:
         strategy:
             fail-fast: false
             matrix:
-                event: ['${{ github.event_name }}']
-                os: ['macos-15', 'ubuntu-24.04', 'windows-2025']
-                exclude:
-                    # On PRs: Only test on Ubuntu
-                    - event: 'pull_request'
-                      os: 'macos-15'
-                    - event: 'pull_request'
-                      os: 'windows-2025'
+                # Only use macOS and Windows runners on WordPress/gutenberg (including pull requests from forks); runs inside forks use Ubuntu only.
+                os: ${{ github.repository == 'WordPress/gutenberg' && fromJSON( '["macos-15", "ubuntu-24.04", "windows-2025"]' ) || fromJSON( '["ubuntu-24.04"]' ) }}
 
         steps:
             - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
 
@@ -33,12 +33,8 @@ jobs:
         if: ${{ github.repository == 'WordPress/gutenberg' || github.event_name == 'pull_request' }}
         strategy:
             matrix:
-                event: ['${{ github.event_name }}']
-                os: ['macos-15', 'ubuntu-24.04', 'windows-2025']
-                exclude:
-                    # On PRs: Only test Ubuntu and Windows
-                    - event: 'pull_request'
-                      os: 'macos-15'
+                # Only use macOS and Windows runners on WordPress/gutenberg (including pull requests from forks); runs inside forks use Ubuntu only.
+                os: ${{ github.repository == 'WordPress/gutenberg' && fromJSON( '["macos-15", "ubuntu-24.04", "windows-2025"]' ) || fromJSON( '["ubuntu-24.04"]' ) }}
 
         steps:
             - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1