Hi, Before updating to Unity 2018.3, we used to have a custom AssetImporter for model types. Doing so, upon importing a new model in the project we could create a prefab for that model. If the prefab already existed, we replaced it. Now, with the Nested Prefabs workflow, I am unable to use the new API. Code (CSharp): if( !File.Exists( destinationPath )) return PrefabUtility.CreatePrefab(destinationPath, modelAsset); else return PrefabUtility.ReplacePrefab(modelAsset, AssetDatabase.LoadAssetAtPath<GameObject>(destinationPath), ReplacePrefabOptions.ReplaceNameBased); Now I am supposed to call SaveAsPrefabAsset instead, as far as I know, in both situations. When I do so, however, I get an ArgumentException saying "Can't save persistent object as a Prefab asset". What should I do to be able to create a prefab from a model by script?