Study Intervention Phase Eligible subjects will complete a baseline assessment of glucose counterregulation by stepped- hyperinsulinemic hypoglycemic clamp prior to starting intervention with the hybrid closed-loop system (MiniMed 670G system, Medtronic Diabetes, Northridge, CA). Unless this system becomes available to the subject via their insurance carrier, one will be provided for them. Subjects will also receive a study glucometer (Contour Next Link 2.4, Bayer, Indianapolis, IN) that communicates with the MiniMed 670G insulin pump for bolus dosing calculation and glucose sensor calibration. Subjects who cannot maintain > 80% (or 6/7 day) compliance with the sensor component as assessed at each study visit may be dropped since less compliance has not been associated with any benefit of CGM to glycemic control and limits the potential for benefit from LGS on hypoglycemia avoidance. Accuracy of the sensor will be assessed at each visit through devise download and interpretation. Study visits will occur weekly for the first month, then monthly until month 6, and then every 3 months until month 18. This schedule will allow for determination of possible benefit from hybrid closed- loop insulin delivery on glucose counterregulation after 6 months of intensive provider support, and then for assessment of the durability or potential further gains in beneficial effects after another 12 months of more typical provider interaction occurring every 3 months. Weekly visits may be performed via telephone with uploading devise data to Care Link for review and interpretation. Uploaded or downloaded insulin delivery, blood and sensor glucose monitoring, insulin dose settings and CGM calibration accuracy, alert settings, time spent in auto and manual modes, and LGS threshold and activity will be assessed at each visit, targeting > 80% CGM and LGS compliance, adjusting basal and bolus insulin dosing in order to minimize glycemic excursions while maximizing hypoglycemia (< 60 mg/dl) avoidance, with adjustment of alarms set to alert the subject to rapidly increasing or decreasing glucose and predict the occurrence of elevated or low blood glucose. During manual mode, target glucose ranges will be 90 - 140 mg/dl before meals, < 180 mg/dl after meals, and 120 - 160 mg/dl at bedtime, with correction dosing to no lower than 100 mg/dl during the day, and 120 mg/dl overnight. Alarm settings may be individualized to target these ranges, but the hypoglycemia alarm for LGS will not be set lower than 70 mg/dl. During auto mode, the automated interprandial basal insulin delivery will adjust according to the closed-loop algorithm to target a sensor glucose of 120 mg/dl, which may be temporality increased to 150 mg/dl if needed to further minimize exposure to hypoglycemia during exercise or overnight. Prior to each 3 monthly visit, subjects will wear an actigraph monitor ( WGT3X-BT, Actigraph LLC,) for three weeks in order to define the nocturnal period. Every 6 months measures of hypoglycemia awareness (Clarke score) and severity (HYPO score), and the glycemic lability index (LI) will be calculated from questionnaires, event diaries, and device downloads, respectively. At 6 months and at 18 months, subjects will again undergo assessment of glucose counterregulation by stepped-hyperinsulinemic hypoglycemic clamp testing.