Technology is of increasing importance for international cooperation, yet theory development in rationalist International Relations has not kept pace. I develop a theoretical framework for explaining cooperative outcomes in the international regulation of technology. I propose that uncertainty and the distribution of material capacities create a severe international collective action problem for novel technologies, which precludes robust cooperative outcomes and thus limits joint gains from the appropriation of technological benefits and from the mitigation of technological risks. While the severity of the collective action problem attenuates over time, in principle enabling greater ambition in cooperative outcomes, sociotechnical lock-in reduces the capacities and incentives of state actors to deviate from pre-existing rules. This leads to incremental change whereby rules harden over time but do not change significantly in terms of their regulatory substance. While early regulatory interventions are hampered by collective action problems, late interventions are constrained by lock-in. These temporal dynamics create a tendency towards systemic inefficiency in international technology regulation. I illustrate this argument using the cases of nuclear power and synthetic biology.