With RESTEASY-1911 and WFLY-6459 JSON-B was changed to be the default serialization for JSON entities. Previously Jackson 2 was used. To keep backwards compatibility if a Jackson annotation was found on a REST endpoint, then Jackson was used over JSON-B. However, this only happens if the endpoint is in a WAR. For EJB JAR deployments this check is skipped preferring JSON-B for serialization.