option() is being called with two Map arguments, but your example does not seem to indicate that you are doing that. It's interesting that 3.7.0 "fixes" it because I can't think of any reason why that would matter. Perhaps you could try 3.6.5 to see if there were somehow changes after 3.6.2 that solved this problem? My question is: does the version of the javascript client match the version of the server (or should it)? Or should I always strive to use the latest client?Generally speaking you should follow the version table here https://docs.aws.amazon.com/neptune/latest/userguide/access-graph-gremlin-client.html - While it is possible that versions outside of those ranges in that table will work with one another, those are the versions that Neptune tests against and that are supported.