OBJECTIVE: Insulin icodec (icodec) is a novel once-weekly basal insulin analog. This trial investigated two approaches for switching to icodec versus once-daily insulin glargine U100 (IGlar U100) in people with type 2 diabetes receiving daily basal insulin and one or more oral glucose-lowering medications. RESEARCH DESIGN AND METHODS: This multicenter, open-label, treat-to-target phase 2 trial randomized (1:1:1) eligible basal insulin-treated (total daily dose 10-50 units) people with type 2 diabetes (HbA(1c) 7.0-10.0% [53.0-85.8 mmol/mol]) to icodec with an initial 100% loading dose (in which only the first dose was doubled [icodec LD]), icodec with no loading dose (icodec NLD), or IGlar U100 for 16 weeks. Primary end point was percent time in range (TIR; 3.9-10.0 mmol/L [70-180 mg/dL]) during weeks 15 and 16, measured using continuous glucose monitoring. Key secondary end points included HbA(1c), adverse events (AEs), and hypoglycemia. RESULTS: Estimated mean TIR during weeks 15 and 16 was 72.9% (icodec LD; n = 54), 66.0% (icodec NLD; n = 50), and 65.0% (IGlar U100; n = 50), with a statistically significant difference favoring icodec LD versus IGlar U100 (7.9%-points [95% CI 1.8-13.9%]). Mean HbA(1c) reduced from 7.9% (62.8 mmol/mol) at baseline to 7.1% (54.4 mmol/mol icodec LD) and 7.4% (57.6 mmol/mol icodec NLD and IGlar U100); incidences and rates of AEs and hypoglycemic episodes were comparable. CONCLUSIONS: Switching from daily basal insulin to once-weekly icodec was well tolerated and provided effective glycemic control. Loading dose use when switching to once-weekly icodec significantly increased percent TIR during weeks 15 and 16 versus once-daily IGlar U100, without increasing hypoglycemia risk.