In an April 2025 note, the International Centre for Settlement of Investment Disputes (ICSID) explores the possibility of inter se modifications of the ICSID Convention to allow appeals of ICSID awards before a standing Appeals Tribunal under the UNCITRAL Draft Statute on ISDS reform. The note was prepared by ICSID as comments to Working Group III. While amendments to the ICSID Convention require unanimous ratification, the note considers how a subset of ICSID Contracting States could agree to replace annulment of awards with appeal among themselves, without affecting non-participating states. This legal feasibility—grounded in Article 41 of the Vienna Convention on the Law of Treaties—could have significant implications beyond ICSID. In particular, it signals a potential pathway for the use of inter se modifications for investment treaty reform, such as proposals to neutralize the Energy Charter Treaty’s (ECT) sunset clause between EU and non-EU parties. This development adds a new dimension to treaty reform discussions by highlighting flexible legal instruments for targeted change.