I had a series of @Model classes with some mandatory attributes and some optional. Pre-move to 18, everything was working fine. After the migration, it reports that every single non-Optional attribute is nil upon trying to save. The error is CoreData related but not sure if its in the Core layer or Swift layer. Sample error (with app data removed) is : SwiftData.DefaultStore save failed with error: Error Domain=NSCocoaErrorDomain Code=1560 "Multiple validation errors occurred." Error Domain=NSCocoaErrorDomain Code=1570 \"%{PROPERTY}@ is a required value.\" UserInfo={NSValidationErrorObject=<NSManagedObject: 0x30388b2a0> NSLocalizedDescription=%{PROPERTY}@ is a required value., NSValidationErrorKey=systemName, NSValidationErrorValue=null}" I have modified the code to provide default values for all constructors in an attempt to see a difference, but get the same errors