In its recent treaties, the European Union (EU) has established a new model of investor-State dispute settlement (ISDS). The EU’s new model entails the replacement of ad hoc arbitration with standing, treaty-based investment tribunals, staffed with judges appointed by the states parties. Awards produced by the EU’s new process will be subject to appellate review on issues of law and fact. The EU has indicated that it will pursue a treaty to multilateralize its new tribunal system. This article addresses the compatibility of the EU’s new ISDS model with existing instruments of the investment treaty regime: first, whether the introduction of an appellate mechanism or, indeed, the total reworking of ISDS to establish investment tribunals, renders instruments like the ICSID Convention and the New York Convention inapplicable to the modified process of ISDS; second, how the integration of any appellate mechanism with existing international investment treaties might technically be achieved.