According to [1] the DynamicFeature interface is supported only as part of the Server API. However, client side processing [2] collects information about client dynamic features even if it looks like they are never used. This should probably be removed.

[1] https://docs.oracle.com/javaee/7/api/javax/ws/rs/container/DynamicFeature.html
[2] https://github.com/resteasy/Resteasy/blob/master/resteasy-core/src/main/java/org/jboss/resteasy/core/providerfactory/ClientHelper.java#L48