Allow JSON payloads to contain "untyped JSON" in addition to OData declared and open properties. Add annotation for structured types that announce the potential presence of untyped JSON, either as a tagging term or by explicitly listing the names of the "untyped JSON" properties: <Annotation Term="Xxx.ContainsUntypedJSON" /> Or <Annotation Term="Xxx.ContainsUntypedJSON"> <Record> <PropertyValue Property="Properties"> <Collection> <String>opaqueJsonProperty</String> <String>Another-untyped/JSON;Property{with:a#weird name</String> </PropertyValue> </Collection> </Record> </Annotation> Allow clients to tell whether they are willing to receive "untyped JSON" via a new preference odata.allow-untyped-json.