BACKGROUND: The advanced hybrid closed loop (a-HCL) algorithm includes automated basal and correction bolus insulin with customizable glucose targets. This study aimed to evaluate the effectiveness of a-HCL compared to predictive low glucose suspension (PLGS) and standard hybrid closed-loop (s-HCL) systems and to identify patient populations experiencing the greatest glycemic improvement after transitioning to a-HCL. METHODS: This retrospective study included type 1 diabetes patients at the University Hospital Zurich, Switzerland, who transitioned from PLGS or s-HCL to a-HCL between January 2020 and December 2021. Glycemic metrics, including HbA1c, time in range (TIR), time above range (TAR), time below range (TBR), sensor glucose (SG), and coefficient of variation (CV), were analyzed pre-and post-a-HCL implementation, considering clinical parameters influencing outcomes. RESULTS: Among 71 patients, a-HCL implementation significantly reduced in HbA1c (7.2 ± 0.9 % to 6.8 ± 0.5 %, p <
0.001), SG (8.8 ± 1.4 mmol/L to 7.8 ± 0.8 mmol/L, p <
0.001), TAR (26.3 % to 17.3 %, p <
0.001) and increased TIR (68.5 % to 79.8 %, p <
0.001). TBR and CV showed no significant changes. Improvements were most pronounced in patients with higher baseline HbA1c, SG, CV and lower TIR, all indicators of poor glycemic control, and a BMI >
30 kg/m CONCLUSIONS: Our findings support a-HCL utilization across all patients, particularly in poorly controlled type 1 diabetes patients.