The Russian invasion of Ukraine has sparked renewed interest in the phenomenon of brain drain: the exodus of human capital out of countries. Yet quantifying brain drain, especially in real time during crisis situations, remains difficult. This hinders our ability to understand its drivers and mechanisms and to anticipate its consequences. To address this gap, I draw on and extend a large scale dataset of the locations of highly active software developers collected in February 2021, one year before the invasion. Revisiting those developers that had been located in Russia in 2021, I confirm a significant exodus of developers from Russia by late June 2022. 8.6% of Russian developers list a new country, compared with 2.4% of developers from comparable countries in the region but not directly involved in the conflict. 11.3% of Russian developers have obscured their location (vs. 1.9% in the comparison set). Our data also allows us to observe heterogeneities in who leaves and who remains, and to see where they are going. Developers leaving Russia were significantly much more active and central in the collaboration network than those who stay behind. This suggests that the most important developers have already left Russia.