Oligodendrocyte development is tightly controlled by extrinsic signals; however, mechanisms that modulate cellular responses to these factors remain unclear. Six-transmembrane glycerophosphodiester phosphodiesterases (GDEs) are emerging as central regulators of cellular differentiation via their ability to shed glycosylphosphatidylinositol (GPI)-anchored proteins from the cell surface. We show here that GDE3 controls the pace of oligodendrocyte generation by negatively regulating oligodendrocyte precursor cell (OPC) proliferation. GDE3 inhibits OPC proliferation by stimulating ciliary neurotrophic factor (CNTF)-mediated signaling through release of CNTFRα, the ligand-binding component of the CNTF-receptor multiprotein complex, which can function as a soluble factor to activate CNTF signaling. GDE3 releases soluble CNTFRα by GPI-anchor cleavage from the plasma membrane and from extracellular vesicles (EVs) after co-recruitment of CNTFRα in EVs. These studies uncover new physiological roles for GDE3 in gliogenesis and identify GDE3 as a key regulator of CNTF-dependent regulation of OPC proliferation through release of CNTFRα.