INTRODUCTION: Insulin efsitora alfa (efsitora) is a basal insulin with a flat pharmacokinetic profile and long half-life, enabling weekly dosing. These attributes may provide stable glucose levels. This exploratory phase 1 study aimed to assess the hypoglycemic risk during experimental conditions that mimic situations encountered in daily life. METHODS: This was a single-site, open-label, two-period, fixed-sequence study in participants with type 2 diabetes (T2D) previously treated with basal insulin. The incidence, duration, and nadir glucose of hypoglycemia were assessed after treatment with efsitora versus insulin glargine (glargine) during three provocation conditions: 24-h prolonged fasting, prolonged fasting with exercise, and double dosing of study insulin. RESULTS: The 54 enrolled adults (BMI 21.8-39.7 kg/m(2), HbA1c 6.5-9.4%) achieved stable fasting glucose before undergoing provocation. Most hypoglycemic events were level 1 ( ≥  54 to < 70 mg/dL) and resolved spontaneously or after oral glucose. The incidences of level 1 hypoglycemia for efsitora and glargine were not significantly different: for prolonged fasting, the incidences were 44.7 vs. 42.6% and the difference in proportion was 2.1% (95% CI: - 17.2, 21.4); for prolonged fasting with exercise, the corresponding values were 65.9 vs. 50.0% and 15.9% (- 3.0, 34.8); for double dosing, the corresponding values were 68.1 vs. 61.7% and 6.4% (- 12.8, 25.6). Level 2 hypoglycemia (< 54 mg/dL) was infrequent during both treatments and all provocations. No severe hypoglycemia was observed. Mean nadir glucose (range 62.8-66.3 mg/dL) and hypoglycemia duration (range 76.6-115.2 min) were also similar for the two treatments, depending on the provocation. CONCLUSION: Overall, weekly efsitora did not increase the incidence, duration, or severity of hypoglycemia compared to daily glargine during provocation periods in patients with T2D. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT04957914.