The main purpose of this study is to evaluate the safety and tolerability of the study drug known as LY4006895. Part A will administer a single-ascending dose in healthy participants or Part B will administer multiple-ascending doses in participants with early symptomatic Alzheimer's Disease (AD). Blood tests will be performed to check how much LY4006895 gets into the bloodstream and how long it takes the body to eliminate it. This is a 2-part study and will last approximately 29 weeks for Part A and 61 weeks for Part B, including a screening period for each part.