Qualified participants include those who are/have: • Between the ages of 18 and 70 years of age with type 1 diabetes mellitus, • Experienced at least one low blood glucose level (hypoglycemia) episode with symptoms during the last month, • Qualify by certain lab tests which will be performed by a study doctor or staff at site, • Receiving at least 1 year treatment with basal plus mealtime insulin, and • Willing to return to clinic for regular site visits and phone contact between appointments.     Participants who do not qualify include those who are/have: • Using any basal insulins other than Lantus, Toujeo, Levemir, or Tresiba in the past three months prior to screening, • Using less than 2 injections of rapid-acting insulin analog per day within 30 days prior to coming into the clinic to be screened for this study, • Using an insulin pump during the last 6 months before coming into the clinic to be screened for this study, • Pregnant or breast-feeding women or planning pregnancy during the duration of the clinical trial, or • Used of any other investigational drug(s) within 1 month or 5 half-lives, whichever is longer prior to screening. • Off-label use of any oral antidiabetic medication or non-insulin injectable agents during the 3 months prior to screening.