Using newly-assembled data from 1980 through 2024, we show that 25% of scientifically-active, US-trained STEM PhD graduates leave the US within 15 years of graduating. Leave rates are lower in the life sciences and higher in AI and quantum science but overall have been stable for decades. Contrary to common perceptions, US technology benefits from these graduates' work even if they leave: though the US share of global patent citations to graduates' science drops from 70% to 50% after migrating, it remains five times larger than the destination country share, and as large as all other countries combined. These results highlight the value that the US derives from training foreign scientists - not only when they stay, but even when they leave.