Background and aims: Shifting to advanced hybrid closed loop (AHCL) systems is associated with improved blood glucose control. We aimed to explore the sustainability over time of the AHCL-related improvement in blood glucose control up to two years and its clinical predictors. Methods: We evaluated 206 adults with type 1 diabetes mellitus, aged 43.5±14.2 years, men 48.3%, baseline Glucose Management Indicator 7.3±2.6%, using MiniMed™ 780G (63%), Tandem Control I-Q (29%), or Yourloops (8%) systems. Demographic and clinical data and continuous glucose monitoring (CGM)-derived metrics were analyzed before and every six months after switching to auto mode. Absolute change in Time in Range (TIR) level between 2-year follow-up and baseline (Delta_TIR) was measured and included in a regression model as dependent variable. Sex, age, type of work, type of HCLS, baseline TIR, time below range, and CV were included as independent variables. Results: A preliminary analysis on 113 participants showed a TIR increase from 64.0±12.0% at baseline to 71.5±10.4% at 6 months, 70.6±11.1% at 1-year, and 69.4±12.9% at 2 years (p<0.001 vs baseline for all, repeated measures post hoc analysis). At multivariable regression analysis, lower baseline TIR (B=-0.584), older age (B=0.200), and use of Yourloops AHCL system (B=-0,160) were significant predictors of Delta_TIR at two years (p<0.001). Conclusions: AHCL use was associated with a rapid improvement in glycemic control lasting to up to 24 months, confirming the safety of the automatic insulin delivery systems. A worse glucose control at baseline and an older age were the main predictors of greater improvement in TIR.