URLi is a novel ultra rapid formulation of insulin lispro that shows improved postprandial glucose control and similar compatibility with continuous subcutaneous insulin infusion (CSII) vs. Humalog. In this study URLi was evaluated for the first time in a hybrid closed-loop system using the Medtronic MiniMed 670G. Primary objective was to compare URLi to Humalog with respect to the percentage of time with glucose values within target range 70-180 mg/dL (%TIR). This double-blind, crossover study included two 4-week treatment periods with URLi or Humalog. After a 2-week lead-in on Humalog, 42 adults with type 1 diabetes using personal MiniMed 670G pumps were randomized to 1 of the 2 treatment sequences with boluses initiated 0-2 minutes before meals. Both treatments achieved good glycemic control with mean TIR >75% (Fig 1). Mean time above and below range met consensus recommendations for both treatments. The percentage of time in Auto Mode was similar between treatments: URLi 92.0%; Humalog 91.4%. Insulin doses and pump settings were generally similar between treatments. There were no serious adverse events or early discontinuations. Overall incidence of treatment-emergent adverse events was similar between treatments. URLi demonstrated comparable glycemic control and a similar safety profile to Humalog with the MiniMed 670G system in patients with type 1 diabetes.