That's not the semantics.  You can set your own arbitrary ProxyServerSelector (an async-http-client interface).  Or, you can set this boolean, which tells async-http-client to use the default JDK ProxySelector (note, ProxySelector is a JDK provided interafec, while ProxyServerSelector is from async-http-client.  The two unfortunately cannot be the same because the JDK one is missing some features that async-http-client already supports).  The behaviour here is implemented to be consistent with the existing behaviour of setUseProxyProperties.