To be slightly pedantic and clarify. It's not actually anything to do with Core Data itself but CloudKit that is doing the syncing, more specifically, NSPersist

To be slightly pedantic and clarify. It's not actually anything to do with Core Data itself but CloudKit that is doing the syncing, more specifically, NSPersistentCloudKitContainer which came out a few years ago and makes adding CloudKit syncing to Core Data a one-liner basically. This year at WWDC we got CKSyncEngine which gives you the primitives to add a CloudKit syncing to your own persistence layer.