The Gen3 iLet (iLet) is a physically and functionally integrated, bionic pancreas (BP) platform that can operate in bihormonal, insulin-only, or glucagon-only modes. The iLet in insulin-only mode has never been tested in subjects <18 years of age. Twenty youth (mean age=12±3 [range 7-17] years) completed a 10-day, randomized crossover study at 3 sites comparing 5 days using the insulin-only iLet to 5 days of usual care (UC) with sensor-augmented pump therapy. During the day, youth were supervised by study staff in a day-camp setting with periods of vigorous physical activity. At night, participants returned home with their guardians, and staff monitored glucose levels remotely. Participants achieved good glycemic control with low levels of hypoglycemia in both the UC and iLet arms (see Table). There were 3 hyperglycemic events associated with iLet malfunction, including one failure of insulin delivery with alarms not heard and two instances of insulin cartridges leaking. These events and others observed by the study teams, guardians, and participants led to changes in the Gen4 iLet under development to improve safety and usability. These results suggest that testing of the improved Gen4 iLet is warranted and offers promise in the pediatric population. Disclosure L. Ekhlaspour: None. G.P. Forlenza: Advisory Panel; Self; Dexcom, Inc. Consultant; Self; Medtronic MiniMed, Inc., Tandem Diabetes Care. Research Support; Self; Dexcom, Inc., Insulet Corporation, Medtronic MiniMed, Inc., Tandem Diabetes Care. C. Berget: Consultant; Self; Insulet Corporation, Medtronic. K.R. Bird: None. K.A. Englert: Consultant; Self; PicoLife Technologies, LLC. L. Hsu: None. C.A. Balliro: None. N. Mauras: Consultant; Self; Novo Nordisk Inc., PicoLife. Research Support; Self; Medtronic MiniMed, Inc. R. Wadwa: Advisory Panel; Self; Eli Lilly and Company. Research Support; Self; Beta Bionics, MannKind Corporation, Novo Nordisk Inc., Tandem Diabetes Care, Xeris Pharmaceuticals, Inc. Other Relationship; Self; Dexcom, Inc. B.A. Buckingham: Advisory Panel; Self; ConvaTec Inc., Novo Nordisk Inc., Profusa, Inc. Consultant; Self; Medtronic MiniMed, Inc. Research Support; Self; Beta Bionics, ConvaTec Inc., Dexcom, Inc., Insulet Corporation, Medtronic MiniMed, Inc., Tandem Diabetes Care. Other Relationship; Self; Insulet Corporation, Tandem Diabetes Care. F. El-Khatib: Employee; Self; Beta Bionics. Stock/Shareholder; Self; Beta Bionics. E. Damiano: Advisory Panel; Self; Novo Nordisk A/S. Board Member; Self; Beta Bionics. Employee; Self; Beta Bionics. Stock/Shareholder; Self; Beta Bionics. Stock/Shareholder; Spouse/Partner; Beta Bionics. Other Relationship; Self; Ascensia Diabetes Care, Senseonics. S.J. Russell: Advisory Panel; Self; Companion Medical, Unomedical a/s. Consultant; Self; Flexion Therapeutics. Research Support; Self; Beta Bionics, MITRE Corporation, Novo Nordisk A/S, Zealand Pharma A/S. Other Relationship; Self; ADOCIA, Ascensia Diabetes Care, Ascensia Diabetes Care, Lilly Diabetes, Roche Diabetes Care, Senseonics. Funding National Institute of Diabetes and Digestive and Kidney Diseases (1UC4DK108612)