For anyone needing Xcode 27 to build SwiftPM packages below its supported deployment target, create an .xcconfig containing: MACOSX_DEPLOYMENT_TARGET[sdk=macosx*] = 10.13 __DIAGNOSE_INVALID_DEPLOYMENT_TARGET_AS_ERROR = NO Then tell Xcode to use it globally: defaults write com.apple.dt.Xcode OverridingXCConfigPath "/path/to/Overrides.xcconfig" Restart Xcode. This applies the deployment target to SPM dependencies too, while turning Xcode 27’s unsupported-target error into a warning.