This study will compare LY900014, a drug that lowers blood sugar, with insulin lispro (Humalog). Both drugs will be given by injection under the skin of the abdomen. This study will be conducted in participants with type 1 diabetes to investigate how quickly and how much LY900014 is absorbed and the effect of LY900014 on blood sugar levels in comparison with insulin lispro. The study will last about 3 to 6 weeks for each participant, not including screening.

Inclusion Criteria:

• Are Japanese male or female participant with a diagnosis of T1DM, based on the World Health Organization classification, for at least 1 year prior to screening
• Have a body mass index (BMI) of 18.5 to 30.0 kilograms per square meter (kg/m²)
• Have a glycated hemoglobin <9.0% at screening

Exclusion Criteria:

• Have, except for current regimen of insulin therapy and concomitant medication(s), regular use of or intended use of any over-the-counter or prescription medications or nutritional supplements that treat hyperglycemia or insulin resistance or that promote weight loss within 14 days before dosing
• Are receiving chronic (lasting longer than 14 consecutive days) systemic or inhaled glucocorticoid therapy (excluding topical, intra-articular, and intraocular preparations), or have received such therapy within the 4 weeks before screening
• Have a history of renal impairment (exclusion only if estimated glomerular filtration rate [GFR] <60 milliliters/minute/1.73 square meters [GFR is estimated according to a formula recommended by the Japanese Society of Nephrology]), or have a serum creatinine level ≥126 micromoles per liter (μmol/L) (>1.42 milligrams per deciliter [mg/dL]) (male) or ≥111 μmol/L (>1.25 mg/dL) (female)
• Have a history of deep vein thrombosis of the leg, or repeated episodes of deep leg vein thrombosis in first-degree relatives (parents, siblings, or children), as determined by the investigator
• Have proliferative retinopathy or maculopathy and/or severe neuropathy; in particular, autonomic neuropathy, as determined by the investigator based on a recent (<1.5 years) ophthalmologic examination
• Have had any significant changes in insulin regimen and/or unstable blood glucose control within the past 3 months prior to screening, as determined by the investigator
• Require daily insulin treatment >1.5 units per kilogram (U/kg)

All randomized participants who received at least 1 dose of study drug.

Baseline up to 56 weeks

All randomized participants.