The official withdrawal of Russia’s ratification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in November 2023 is one of the most significant and legally complicated events of the modern international arms-control law. The Russian Federation has created a sense of urgent inquiries in the interpretation and sustainability of interim treaty responsibilities under Article 18 of the 1969 Vienna Convention on the Law of Treaties (VCLT) by withdrawing the instrument of ratification deposited in 2000. That provision requires the states which have signed or ratified a treaty pending entry into force to refrain from acts which would defeat the object and purpose of the treaty. The present article holds the view, based on a systematic analysis of the text of treaties, International Law Commission (ILC) commentary, and comparative state practice, that Russia de-ratification was not sufficiently clear not to become a party under Article 18(a) VCLT, and thus that Russia is bound by the interim obligation of not to hold nuclear explosive tests. The analysis identifies the difference between de-ratification and formal unsigning and the practice of the United States in relation to the Rome Statute of the International Criminal Court and the Arms Trade Treaty as paradigmatic comparators and assesses whether the exception of Article 18(b) of the prolonged non-entry into force has been imposed by the CTBT. The paper ends up by offering implications to compliance monitoring, treaty law doctrine and the nuclear testing taboo.