The purpose of this study is to evaluate how well LY4057996 is tolerated and what side effects may occur in healthy participants and participants with Type 1 and Type 2 Diabetes. The study drug will be administered either subcutaneously (SC) (under the skin) or intravenously (IV) (into a vein in the arm). Blood tests will be performed to check how much LY4057996 gets into the bloodstream and how long it takes the body to eliminate it. The study will last 11 weeks for Part A1-A2, 4 weeks for A3-A5, 6 weeks for Part B and 7 weeks for Part C, all approximations, excluding a screening period.