Brain drain outweighs brain circulation between the Global North and South

International research mobility is increasing, as is the expectation that high- and low-income countries will mutually benefit. The once-dominant view of research mobility as “brain drain” has been replaced by a more optimistic narrative of “brain circulation”, built on the idea of cyclical talent flows that advantage all countries involved. But does this brain circulation model reflect the full picture for low- and middle-income countries, whose development depends on producing and retaining scientific talent? Our analysis of 16 years of international mobility flows in science suggests otherwise. While brain circulation increasingly occurs through temporary positions, joint affiliations, and return migration, a persistent pattern of brain drain remains, with Global South countries losing a growing share of their best-performing scientists to the Global North. Moreover, a differentiated hierarchy of talent flows is visible within the Global South. Some of the countries that lose the most talent to the Global North also attract the most talent from other Global South nations, offsetting their losses. But many others see substantial outflows of local talent to both the Global North and other Global South regions, compounding the issue. This differentiated pattern is also visible in the multiplex network structure of national inflows and outflows, where the relationship between sending talent to the Global North and receiving talent from the Global South is weaker than one would expect in random networks with a similar structure. Overall, our findings suggest a mixed reality. While visiting and return migration likely produce mutual benefits for Global North and Global South countries alike, this talent circulation is unlikely to offset the Global South's direct and indirect loss of its best-performing scientists.