Extended Cascading-E Notation (xE^) is a notation by Sbiis Saibian, and the most recent component of the Extensible-E System. It extends upon Cascading-E notation by applying up-arrow notation to hyperions (#). The limit of its growth rate is comparable to \(f_{\varphi(\omega,0,0)}(n)\). The Extensible-E System includes xE^ and all extensions to come.