Hypoxia promotes isocitrate dehydrogenase (IDH2)-dependent carboxylation of α-ketoglutarate to citrate, supporting cell growth and viability. Under normoxic conditions, citrate is synthesized from glucose-derived acetyl-CoA and glutamine-derived oxaloacetate via the TCA cycle. However, in hypoxia, glucose-dependent citrate production declines, and glutamine becomes the primary source of citrate. In hypoxic cells, glutamine-derived α-ketoglutarate is reductively carboxylated by IDH2 to form isocitrate, which is then isomerized to citrate. This process is associated with increased synthesis of 2-hydroxyglutarate (2HG) and is critical for maintaining citrate levels and cell proliferation. Hypoxic cells require glutamine for citrate synthesis, and its deprivation leads to cell death. The reductive carboxylation of glutamine-derived α-ketoglutarate is part of the metabolic reprogramming associated with hypoxia-inducible factor 1 (HIF1). Constitutive HIF1 activation recapitulates the preferential reductive metabolism of glutamine-derived α-ketoglutarate even in normoxic conditions. In hypoxia, IDH2 is essential for reductive carboxylation of α-ketoglutarate to citrate, and its knockdown impairs cell proliferation. These findings highlight the role of IDH2 in maintaining citrate synthesis and cell growth under hypoxic conditions. The study also shows that hypoxic cells preferentially synthesize citrate through reductive carboxylation rather than oxidative metabolism, and that this process is supported by HIF1 activity. The results demonstrate that IDH2-mediated reductive carboxylation is crucial for citrate production in hypoxic cells and that this pathway is important for hypoxic cell proliferation. The findings have implications for understanding cancer metabolism and the metabolic reprogramming associated with hypoxia.Hypoxia promotes isocitrate dehydrogenase (IDH2)-dependent carboxylation of α-ketoglutarate to citrate, supporting cell growth and viability. Under normoxic conditions, citrate is synthesized from glucose-derived acetyl-CoA and glutamine-derived oxaloacetate via the TCA cycle. However, in hypoxia, glucose-dependent citrate production declines, and glutamine becomes the primary source of citrate. In hypoxic cells, glutamine-derived α-ketoglutarate is reductively carboxylated by IDH2 to form isocitrate, which is then isomerized to citrate. This process is associated with increased synthesis of 2-hydroxyglutarate (2HG) and is critical for maintaining citrate levels and cell proliferation. Hypoxic cells require glutamine for citrate synthesis, and its deprivation leads to cell death. The reductive carboxylation of glutamine-derived α-ketoglutarate is part of the metabolic reprogramming associated with hypoxia-inducible factor 1 (HIF1). Constitutive HIF1 activation recapitulates the preferential reductive metabolism of glutamine-derived α-ketoglutarate even in normoxic conditions. In hypoxia, IDH2 is essential for reductive carboxylation of α-ketoglutarate to citrate, and its knockdown impairs cell proliferation. These findings highlight the role of IDH2 in maintaining citrate synthesis and cell growth under hypoxic conditions. The study also shows that hypoxic cells preferentially synthesize citrate through reductive carboxylation rather than oxidative metabolism, and that this process is supported by HIF1 activity. The results demonstrate that IDH2-mediated reductive carboxylation is crucial for citrate production in hypoxic cells and that this pathway is important for hypoxic cell proliferation. The findings have implications for understanding cancer metabolism and the metabolic reprogramming associated with hypoxia.