The objective of this study is to evaluate glycemic control of users of the AHCL system MiniMed 780G with GS4 calibration-free sensor in children and adolescents with newly diagnosed T1D implemented directly upon T1D diagnosis in combination with continuous glucose monitoring system (CGMS) compared with those treated with MDI retrieved from historical data- in a single- arm open-label prospective observational study, assessed at 3 months. After the initial study period there will be a 3month extension phase of the study.

Inclusion Criteria:

1. Clinical diagnosis of type 1 diabetes (WHO criteria). Diagnosis of type 1 diabetes is based on international criteria and the investigator's judgment; C peptide level and antibody determinations are not required.
2. Age range 7 to 17 years.
3. Literate in Greek or English.
4. Willing to wear study devices.
5. Willing to follow study-specific instructions.
6. Total daily insulin dose greater than 8.0 units over 1 week period
7. Willing and able (access to internet from home) to download information into the Medtronic CareLink software
8. Clinically eligible to start the AHCL system

Exclusion Criteria:

• Type 2 diabetes mellitus or MODY diabetes
• Any untreated comorbidities of type 1 diabetes
• Medication affecting metabolic control or interfering in the interpretation of HbA1c
• Pregnancy
• Untreated diabetes retinopathy, or other causes that in the investigator's opinion, precludes the individual from participating in the trial.
• Known or suspected allergy to insulin.
• Regular use of acetaminophen.
• Lack of reliable telephone facility for contact.
• Living alone.
• Severe visual or hearing impairment.
• Medically documented allergy to the adhesive of plasters or unable to tolerate tape adhesive around sensor placement.
• Serious skin lesions at areas of the body used for insertion of the glucose sensor.
• Illicit drugs abuse.
• Alcohol abuse.
• Sickle cell disease, haemoglobinopathy, receiving red blood cell transfusion or erythropoietin within 3 months prior to time of enrollment.
• Eating disorder including anorexia/bulimia.
• Milk protein allergy.

This study is a single-center open-label, single arm, trial, comparing advanced hybrid closed-loop (AHCL) insulin delivery and standard insulin therapy with multiple daily injections (MDI) (historical data- control) over a period of 3 months in newly diagnosed type 1 diabetes children and adolescents hospitalized and followed at the Diabetes center of the First Department of Pediatrics of the Medical School of the National and Kapodistrian University of Athens, Athens, Greece. After the initial 3 months, there will be an extension phase of the study, for another 3 months (total 6 months).

A total of 30-35 individuals (aged 7-17 years) will be enrolled to reach 25-30 individuals who will complete the 3-months' study. The expected number of participants is based on the last 3 years data of our Diabetes Center, where the total number of newly diagnosed children/ adolescents with T1D (and those over 7 years of age) in our Center was as follows, in 2022: 56 (36), in 2023: 63 (47), in 2024.