Inclusion Criteria:  Adult and adolescent male and female subjects >age 14 years Clinical diagnosis of Type 1 diabetes for at least one year Experienced Control-IQ technology user for ≥3 months. Use of Control-IQ technology in closed-loop at least 80% of the 2-week time period before screening. Not pregnant or planning a pregnancy during the time period of the study Using only Humalog U-100 or Novolog U-100 insulin ICR and ISF optimized per investigator judgement CGM time in range (70-180 mg/dL) at least 50% on Control-IQ technology Has current glucagon product to treat severe hypoglycemia (injectable or nasal) at home (will provide prescription if they do not have one)  Willing to:  Share Dexcom G6 CGM data with study staff and Tandem Share t:connect data with Tandem Eat meals with known carbohydrate amounts Take meal boluses as directed (use of different options as scheduled and instructed) Follow study Glycemic Treatment Guidelines for hypo and hyperglycemia Keep food and exercise diary Set accurate sleep schedule on pump Exercise while using exercise activity in Control-IQ technology at least twice weekly Complete questionnaires before and after using investigational device Sign an informed consent form Willingness to use the Dexcom G6 app on their personal phone throughout the study, and share real time CGM information with a local contact and study staff Availability of a local contact who has access to the study participant, knows their whereabouts, and agrees to be promptly available if contacted by study staff. If the subject lives alone, the local contact must live within 30 minutes and have access to the subject overnight.  Exclusion Criteria:  Diabetic ketoacidosis (DKA) in the past 6 months Severe hypoglycemia (needing assistance) in the past 6 months Inpatient psychiatric treatment in the past 6 months History of drug abuse (defined as any illicit drug use) or history of alcohol abuse prior to screening or is unwilling to agree to abstain from illicit drugs throughout the study History of heart, lung or kidney disease determined by the investigator to interfere with the study Use of glucocorticoids, beta blockers or other medications determined by investigator to interfere with the study Use of long-acting insulin or any non-insulin glucose lowering agents (i.e. SGLT-2 inhibitor) other than metformin Use of Afrezza during the study period Febrile illness within 3 days of the start of the study Subject is pregnant or lactating or intending to become pregnant before or during participation in this study For subjects >50 years old or with diabetes duration >20 years who will be exercising as part of the 48 hour study, abnormal electrocardiogram consistent with increased risk of arrhythmia, ischemia, or prolonged QTc interval (> 450 ms) Significant chronic kidney disease (eGFR < 60) or hemodialysis Significant liver disease History of adrenal insufficiency History of abnormal TSH consistent with hypothyroidism or hyperthyroidism that is not appropriately treated