A Study of Remternetug (LY3372993) in Early Alzheimer's Disease (TRAILRUNNER-ALZ 3)

Inclusion Criteria: * Have a phosphorylated tau (P-tau) result consistent with the presence of amyloid pathology. * Have a reliable study partner and backup study partner familiar with overall function and behavior, such as day-to-day activities and cognitive abilities. * Have adequate literacy, vision, and hearing for neuropsychological testing at screening. * Have a Mini Mental Status Exam (MMSE) score consistent with no to minimal cognitive impairment. * Have a Functional Activities Questionnaire (FAQ) score consistent with no to minimal functional impairment. * If currently receiving medications as symptomatic treatment for AD, dose has been stable for at least 30 days before screening. Exclusion Criteria: * Have dementia or significant other neurological disease that can affect cognition. * Have current serious or unstable illnesses that in the investigator's opinion, could interfere with the analyses of the study. * Have a history of cancer that, in the investigator's opinion, has a high risk of recurrence. * Have a history of clinically significant multiple or severe drug allergies, or hypersensitivity reactions. * Have a clinically important laboratory test result or other abnormality as determined by investigator, prior to randomization, that could be detrimental to the participant or could compromise the study. * Have any contraindications for magnetic resonance imaging (MRI). * Have a centrally read MRI that does not meets study entry criteria. Prior or Current Therapies * Have ever had prior treatment with a passive anti-amyloid immunotherapy. * Have received active immunization against Aβ in any other study.