Insulin icodec is a basal insulin in development for once-weekly (OW) dosing. The aim of this study was to compare the hypoglycemia frequency and response after icodec vs. insulin glargine U100 (IGlar) overdosing. In a randomized, open-label, two-period crossover trial, 43 individuals with T2D on basal insulin±metformin (mean±SD age 56±9 yrs, HbA1c 7.2±0.7%) received OW icodec for 6 weeks and once-daily IGlar for 12 days at equimolar total weekly doses based on the individual daily run-in IGlar dose (mean 30±14 U) titrated to a fasting SMPG target of 80-130 mg/dL. Once at steady state, double (DD) and triple (TD) doses of icodec and IGlar were followed by hypoglycemia induction 44 h (icodec) or 7 h (IGlar) post-dose (expected time of maximum glucose-lowering effect) : First, euglycemia was maintained at 100 mg/dL by variable i.v. glucose. Then, PG was allowed to decrease to a nadir of no less than 45 mg/dL maintained for 15 min. Euglycemia was restored by constant i.v. glucose. Hypoglycemic symptom score (HSS) and counterregulatory hormones were assessed at PG 100 mg/dL and at predefined PG levels until nadir PG. For DD, clinically significant hypoglycemia (PG<54 mg/dL) occurred in 40 vs. 36% of subjects for icodec vs. IGlar (odds ratio 1.28; p=0.63) . For TD, clinically significant hypoglycemia occurred in 53 vs. 70% of subjects (odds ratio 0.48; p=0.14) , mean nadir PG was 56 vs. 52 mg/dL (treatment ratio 1.07; p<0.001) , change in HSS at nadir PG was comparable for icodec vs. IGlar (treatment difference 0.46; p=0.77) , responses in adrenaline, noradrenaline and cortisol during hypoglycemia development were greater for icodec vs. IGlar, while glucagon and growth hormone levels increased similarly. In conclusion, a DD or TD of once-weekly insulin icodec does not lead to increased risk of hypoglycemia compared to once-daily IGlar. During hypoglycemia, a comparable symptomatic response and a moderately greater endocrine response were seen for icodec vs. IGlar. Disclosure E.Svehlikova: n/a. K.Niss arfelt: Employee; Novo Nordisk. R.Cailleteau: Employee; Novo Nordisk A/S, Stock/Shareholder; Novo Nordisk A/S. S.Deller: None. K.Thomsen: Employee; Novo Nordisk. M.Hart: None. I.Mursic: None. T.Pieber: Advisory Panel; Arecor, Novo Nordisk A/S, Research Support; AstraZeneca, European Union, JDRF, Novo Nordisk Foundation, Sanofi, Speaker's Bureau; Novo Nordisk A/S, Roche Diagnostics. H.Haahr: Employee; Novo Nordisk A/S, Stock/Shareholder; Novo Nordisk A/S. Funding Novo Nordisk