Inclusion Criteria:

• Clinical diagnosis of type 1 diabetes.
• Age ≥ 65 years old.
• T1D Duration of at least 1 year.
• HbA1c < 10.0% from point of care or local lab at time of screening visit.
• Insulin regimen involves basal/bolus insulin via insulin pump or multiple daily injections.
• Most recent GFR ≥ 30 ml/min/m2 from local lab within the past 6 months.
• Willingness to use a rapid acting insulin compatible with the Tandem t:slim X2 pump (currently aspart and lispro; other rapid acting insulins likely to be approved for pump use prior to study initiation such as Fiasp).
• Familiarity with and willingness to use a carbohydrate ratio for meal boluses.
• Willing to use study devices and automated insulin delivery features.
• Participant is independently managing his/her diabetes with respect to insulin administration and glucose monitoring (may include assistance from spouse or other caregiver)
• Participant understands the study protocol, agrees to comply with it and is able to successfully pass the consent understanding assessment with no more than 2 attempts. 
• Participant comprehends written and spoken English.
• At least 240 hours of CGM readings available during the end of run-in assessment.
• At least 1.5% of time with CGM glucose levels < 70 mg/dL prior to SAP initiation.

Exclusion Criteria:

• Use of PLGS technology or HCL insulin delivery in the past 3 months.
• History of 1 or more Diabetic Ketoacidosis episodes in the previous 6 months.
• Clinical diagnosis by a primary care provider, neurologist or psychiatrist of dementia, in the investigator’s opinion a suspected severe cognitive impairment such that it would preclude ability to understand the study or use devices, or ascore of 13 or less on the Montreal Cognitive Assessment (mild cognitive impairment is not an exclusion)
• A condition, which in the opinion of the investigator or designee, would put the participant or study at risk, including severe vision or hearing impairment and any contraindication to the use of any of the study devices per FDA labeling.  
• Known adhesive allergy or skin reaction during the run-in pre-randomization phase or previous difficulty with pump and CGM insertions that would preclude participation in the randomized trial.
• Concurrent use of any non-insulin glucose-lowering agent other than metformin (including GLP-1 agonists, Symlin, DPP-4 inhibitors, SGLT-2 inhibitors, sulfonylureas).
• Stage 4 or 5 renal disease.
• The presence of a significant medical or psychiatric condition or use of a medication that in the judgment of the investigator may affect completion of any aspect of the protocol, or is likely to be associated with life expectancy of < 1 year.