A Study of t:Slim X2 With Control-IQ Technology

The purpose of this study is to learn whether an investigational automated insulin delivery system ("study system") for children with type 1 diabetes can safely improve blood glucose (sometimes called blood sugar) control. The system uses continuous glucose monitoring (CGM), an insulin pump, and a software algorithm to automatically give insulin and control blood glucose. This is called a "closed-loop control" system.

After consent is signed, eligibility will be assessed. Eligible participants not currently using an insulin pump and Dexcom CGM with minimum data requirements will initiate a run-in phase of 2-4 weeks that will be customized based on whether the participant is already a pump or CGM user. Participants who skip or successfully complete the run-in will be randomly assigned 3:1 to the use of closed-loop control (CLC group) using t:slim X2 with Control-IQ Technology vs. Control Group for 16 weeks. The Control Group will be offered to transition to use CLC and the experimental arm will extend their use of CLC for 12 weeks.

Eligibility Criteria:
Inclusion Criteria:

1. Clinical diagnosis, based on investigator assessment, of type 1 diabetes for at least one year and using insulin for at least 6 months
2. Familiarity and use of a carbohydrate ratio for meal boluses.
3. Age ≥ 6 and ≤ 13 years old
4. Weight ≥25 kg and ≤140 kg
5. For females, not currently known to be pregnant If female and sexually active, must agree to use a form of contraception to prevent pregnancy while a participant in the study. A negative serum or urine pregnancy test will be required for all females of child-bearing potential. Participants who become pregnant will be discontinued from the study. Also, participants who during the study develop and express the intention to become pregnant within the timespan of the study will be discontinued.
6. Living with one or more parent/legal guardian knowledgeable about emergency procedures for severe hypoglycemia and able to contact emergency services and study staff.
7. Willingness to suspend use of any personal closed loop system that they use at home for the duration of the clinical trial once the study CGM is in use
8. Investigator has confidence that the participant can successfully operate all study devices and is capable of adhering to the protocol
9. Willingness to switch to lispro (Humalog) or aspart (Novolog) if not using already, and to use no other insulin besides lispro (Humalog) or aspart (Novolog) during the study for participants using to t:slim X2. This includes:

   * Participants randomized to Control IQ
   * Participants on the SAP group on MDI treatment that will be provided a Tandem pump to switch to CSII
   * Participates that are already in Continuous Subcutaneous Insulin Infusion (CSII) randomized to SAP during the extension phase when transition to Control IQ
10. Total daily insulin dose (TDD) at least 10 U/day
11. Willingness not to start any new non-insulin glucose-lowering agent during the course of the trial
12. Participant and parent(s)/guardian(s) willingness to participate in all training sessions as directed by study staff.

Exclusion Criteria:

1. Concurrent use of any non-insulin glucose-lowering agent other than metformin (including glucagon-like peptide \[GLP-1\] agonists, Symlin, dipeptidyl peptidase 4 \[DPP-4\] inhibitors, sodium-glucose cotransporter-2 (SGLT2) inhibitors, sulfonylureas).
2. Hemophilia or any other bleeding disorder
3. A condition, which in the opinion of the investigator or designee, would put the participant or study at risk (specified on the study procedure manual)
4. Participation in another pharmaceutical or device trial at the time of enrollment or during the study
5. Employed by, or having immediate family members employed by Tandem Diabetes Care, Inc., or having a direct supervisor at place of employment who is also directly involved in conducting the clinical trial (as a study investigator, coordinator, etc.); or having a first-degree relative who is directly involved in conducting the clinical trial