This 522 post-market surveillance study is a single-arm, decentralized prospective observational cohort study designed to collect safety data on Control-IQ technology v1.5 in children with type 1 diabetes ages 2 to <6 years old. Participants will use Control-IQ technology v1.5 for 12 months in the real-world setting.

The study will recruit participants age 2 to <6 years old who begin Control-IQ technology v1.5 use in the real-world setting, with a goal of a minimum of 120 completers at 12 months. All enrolled participants will be monitored from baseline through 12 months following the initiation of therapy with the Control-IQ 1.5 system. The primary endpoint is the risk of diabetic ketoacidosis (DKA) and severe hypoglycemia (SH) events. Secondary outcomes include CGM time in range measurements, and patient reported outcomes.

Inclusion Criteria:

• Self-reported type 1 diabetes who have been prescribed the Control-IQ 1.5 system in the t:slim X2 or Mobi insulin pump
• Age 2 to <6 years at time of screening
• Using an insulin approved for use in the pump
• Using an iCGM sensor approved for use with the pump
• Agreement to use Control-IQ technology 1.5, and to continue use for at least 12 consecutive months after study enrollment.
• Agree to provide HbA1c result, obtained within the 6-month period prior to enrollment.
• Ability for parent/guardian to respond to alerts and alarms, and to provide basic diabetes self-management.
• Reside full-time in the United States.
• Willingness to download the t:connect Mobile application to their smartphone and keep it active throughout the study if using a Tandem t:slim X2 pump. Participants who are unable to use the t:connect mobile application must be willing to manually upload their insulin pump data to Tandem Source every three months and at the completion of the study.
• Participant's parent/guardian has read, understood and agreed to participate in the study, and has electronically signed the Informed Consent Form (ICF).

Exclusion Criteria:

• Use of any glucose-lowering therapy other than insulin.
• A medical or other condition, or medications being taken that in the investigator's judgement would be a safety concern for participation in the study.

Enrollment in the study will be available to all individuals age 2 to <6 years of age at time of screening who start therapy with Control-IQ Technology v1.5.