Adaptive Biobehavioral Control (ABC) in a Closed-Loop System (ABC-WIT)

Inclusion Criteria: Age ≥18.0 and ≤70 years old at time of consent Clinical diagnosis, based on investigator assessment, of type 1 diabetes for at least one year Currently using an insulin pump for at least six months Currently using insulin for at least six months Currently using the t:slim X2 insulin pump for at least two months Currently using or anticipated to be using the t:slim X2 insulin pump with Control-IQ technology at randomization (Visit 3). Using or willing to use insulin parameters such as carbohydrate ratio and correction factors consistently on their pump in order to dose insulin for meals or corrections Access to internet and willingness to upload data during the study as needed Willing to use an app on a smart phone during the study. For females, not currently known to be pregnant or breastfeeding If female, sexually active, and of childbearing potential, 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 childbearing 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. Willingness to use only insulin analogs approved for use in the t:slim X2 pump such as lispro (Humalog) or as part (Novolog) and not use ultra-rapid acting insulin analogs (e.g., FiAsp) during the study Total daily insulin dose (TDD) at least 10 units per day Willingness not to start any new non-insulin glucose-lowering agent during the course of the trial (including metformin (biguanides), GLP-1 receptor agonists, pramlintide, DPP-4 inhibitors, SGLT-2 inhibitors, sulfonylureas) An understanding and willingness to follow the protocol and signed informed consent Exclusion Criteria: Concurrent use of any non-insulin glucose-lowering agent other than metformin or GLP-1 receptor agonists following screening (including pramlintide, DPP-4 inhibitors, SGLT-2 inhibitors, sulfonylureas) A condition, which in the opinion of the investigator or designee, would put the participant at risk or interfere with the completion of the protocol. History of diabetic ketoacidosis (DKA) in the 12 months prior to enrollment Severe hypoglycemia resulting in seizure or loss of consciousness in the 12 months prior to enrollment Currently being treated for a seizure disorder Hemophilia or any other bleeding disorder Planned surgery during study duration Participation in another pharmaceutical or device trial at the time of enrollment or during the study Having a direct supervisor at place of employment who is also directly involved in conducting the clinical trial (e.g., study investigator, coordinator, etc.); or having a first-degree relative who is directly involved in conducting the clinical trial.