Following type 1 diabetes (T1D) diagnosis, declining C-peptide levels reflect deteriorating β cell function. However, the precise C-peptide levels that indicate protection from severe hypoglycemia remain unknown. In this issue of the JCI, Gubitosi-Klug et al. studied participants from the landmark and ongoing Diabetes Control and Complications Trial (DCCT) and the Epidemiology of Diabetes Interventions and Complications (EDIC) study that had long-standing (about 35 years) T1D. The authors correlated severe hypoglycemia and other disease outcomes with residual C-peptide levels. While C-peptide secretion failed to associate with hemoglobin A1c (HbA1c) or microvascular complications, C-peptide levels greater than 0.03 nmol/L were linked with fewer episodes of severe hypoglycemia. These findings suggest that efforts to preserve finite β cell function early in T1D can have meaningful, long-standing health benefits for patients.