Gremlin Server currently returns "detached" graph elements. This approach can be expensive for a Vertex as it means that the graph has to get all the properties and serialize them - especially true for graphs with multi-properties.
This issue is to provide an option for Gremlin Server to return "reference" graph elements which only return the id of the element. The default option will continue to be "detached" so as not to introduce a breaking change. We can consider at a later date whether or not to switch the default.