Not official, obviously, but the re-graph integration test server has subscriptions https://github.com/oliyh/re-graph/blob/master/test/re_graph/integration_server.clj

I guess my project is as official as it gets, as it’s mentioned in the docs, (by my own pr), https://github.com/openweb-nl/kafka-graphql-examples/tree/master/graphql-endpoint. If you have specific questions, just put them here.