AimTo evaluate the effectiveness and safety of insulin glargine 300 U/mL (Gla‐300) initiation according to diabetes duration (DD).Materials and MethodsWe analysed patient‐level data from 2381 insulin‐naïve individuals with type 2 diabetes (T2D), of whom 2349 (98.7%) were treated with Gla‐300 for 24 weeks. Of the 2381 participants, 1048 (44.0%) had a DD of less than 8 years and 1333 (56.0%) had a DD of 8 years or longer. We further analysed the subgroups of participants having a DD of less than 4 years (N = 450), 4‐8 years (N = 598), 8‐12 years (N = 627) and 12 years or longer (N = 706).ResultsMean ± standard deviation age was 60.2 ± 9.0 years in participants with a DD less than 8 years and 64.2 ± 8.8 years in those with a DD of 8 years or longer. At 24 weeks of Gla‐300 therapy, HbA1c improved with a least‐squares (LS) mean change from baseline of −1.88% (95% confidence interval [CI], −1.95 to −1.80) and −1.71% (95% CI, −1.77 to −1.65), respectively, resulting in a LS mean difference between groups of 0.17% (95% CI, 0.07 to 0.26; P = .0005). In the subgroup analysis, LS mean HbA1c reduction from baseline to week 24 was highest in participants with a DD of less than 4 years and lowest in participants with a DD of 12 years or longer. Overall, incidences of symptomatic and severe hypoglycaemia were low, irrespective of DD, without body weight changes.ConclusionsGla‐300 was effective and safe in insulin‐naïve individuals with T2D, regardless of DD. Improvement in HbA1c was greater when Gla‐300 was initiated in participants with a DD of less than 4 years, although the difference between the groups was modest.