Subjects will use the Omnipod Horizon™ System in Manual Mode in an outpatient setting for 14-days. Subjects will be trained to use the Manual Mode feature of the Omnipod Horizon™ System including how to use the bolus calculator using manual entry of blood glucose values or by using the CGM-informed bolus calculator.

The study schedule consists of two outpatient phases:

1. 7 days of Omnipod Horizon™ use in Manual Mode without a connected CGM using manual entry of BG values to deliver boluses (Phase 1) followed by;
2. 7 days of Omnipod Horizon™ use in Manual Mode with a connected CGM using the CGM-informed bolus calculator to deliver boluses (Phase 2)

Following subject screening, system training and enrollment, subjects will commence the first 7-day Manual Mode phase of the study.

Subjects will be trained to use the Manual Mode feature of the system including how to use the bolus calculator using manual entry of BG values or by using the CGM-informed bolus calculator.

After completion of the first 7 days of the Manual Mode phase using the Omnipod Horizon™ without a connected CGM, subjects will transition to the next 7 days of the Manual Mode phase using the system with a connected CGM using the CGM-informed bolus calculator to deliver boluses.

Inclusion Criteria:

1. Age at time of consent/assent 2-70 years
2. Subjects aged < 18 years must be living with parent/legal guardian
3. Diagnosed with type 1 diabetes for at least 6 months. Diagnosis is based on investigator's clinical judgment
4. Must be a current Omnipod user, or have used an Omnipod in the past
5. Investigator has confidence that the subject, parent, or legal guardian, can successfully operate all study devices and can adhere to the protocol
6. Willing to use only the following types of Insulin during the study: Humalog, Novolog, Admelog, or Apidra
7. Must be willing to use the Omnipod Horizon™ in Manual Mode only and agree not to use Automated Mode functionality
8. Must be willing to use the Omnipod Horizon™ bolus calculator without a connected CGM for the first 7-days of Manual Mode (Phase 1) while manually entering BG values to deliver boluses
9. Must be willing to use the Omnipod Horizon™ bolus calculator with a connected CGM for the last 7-days of Manual Mode (Phase 2) using the CGM-informed bolus calculator to deliver boluses
10. Willing to wear the system continuously throughout the study
11. For subjects not currently enrolled in the Omnipod Horizon™ Pivotal Study (G190270), A1C <10%
12. Must be willing to use the Dexcom App on the Omnipod Horizon™ PDM as the sole source of Dexcom data (except for the Dexcom Follow App)
13. Able to read and speak English fluently (if subject is a young child then Caregiver must meet the criteria)
14. Willing and able to sign the Informed Consent Form (ICF) and/or has a parent/guardian willing and able to sign the ICF. Assent will be obtained from subjects aged < 18 years per State requirements.
15. For subjects aged 2-5.9 years of age, parents or trained caregivers agree to be physically present during the decision and delivery of insulin boluses for this age group, as well as agree to be available for glucose monitoring and treatment during the 4-hour post bolus period.

Exclusion Criteria:

1. A medical condition, which in the opinion of the investigator, would put the subject at an unacceptable safety risk
2. History of severe hypoglycemia in the past 6 months
3. History of DKA in the past 6 months, unrelated to an intercurrent illness or infusion set failure
4. Plans to receive blood transfusion over the course of the study
5. Currently diagnosed with anorexia nervosa or bulimia
6. Acute or chronic kidney disease or currently on hemodialysis
7. History of adrenal insufficiency
8. Has taken oral or injectable steroids within the past 8 weeks or plans to take oral or injectable steroids during the study
9. Unable to tolerate adhesive tape or has any unresolved skin condition in the area of sensor or pump placement
10. Plans to use insulin other than U-100 insulin intended for use in the study device during the study
11. Use of non-insulin anti-diabetic medication other than metformin (e.g. GLP1 agonist, SGLT2 inhibitor, DPP-4 inhibitor, pramlintide)
12. Current or known history of coronary artery disease that is not stable with medical management, including unstable angina, or angina that prevents moderate exercise despite medical management, or a history of myocardial infarction, percutaneous coronary intervention, or coronary artery bypass grafting within the previous 12 months
13. Clinical signs of hypothyroidism and hyperthyroidism
14. Pregnant or lactating, or is a woman of childbearing potential and not on acceptable form of birth control (acceptable includes abstinence, condoms, oral/injectable contraceptives, IUD or implant)
15. Currently participating or plans to participate in another clinical study using an investigational drug or device other than Omnipod Horizon™. Subjects may be recruited from the Omnipod Horizon Pivotal Study (G190270) prior to their recommencement of the pivotal study after study pause.
16. Unable to follow clinical protocol for the duration of the study or is otherwise deemed unacceptable to participate in the study per the investigator's clinical judgment

First day of Phase 1 to last day of Phase 2, an average of 14 days.