A Study of Remternetug (LY3372993) in Participants With Alzheimer's Disease (TRAILRUNNER-ALZ 1)

Inclusion Criteria: * Gradual and progressive change in cognitive function ≥6 months prior to screening. * A Mini-Mental (MMSE) score of 20 to 30 (inclusive) at screening. * Has an amyloid PET scan result consistent with the eligibility criteria. * Have a reliable study partner who will provide written informed consent to participate and is in frequent contact with the participant. * Have adequate literacy, vision, and hearing for the neuropsychological testing in the opinion of the investigator at the time of screening. * Are reliable and willing to make themselves available for the duration of the study and are willing to follow study procedures. * Males and females will be eligible for this study. * Women not of childbearing potential (WNOCBP) may participate in this trial. Exclusion Criteria: * Current serious or unstable illnesses that, in the investigator's opinion, could interfere with the analyses in this study; or has a life expectancy of \<24 months. * History of cancer with high risk of recurrence and preventing completion of the trial. * Participants with any current primary psychiatric diagnosis other than AD that in the investigator's opinion, is likely to confound interpretation of the drug effect, affect cognitive assessment, or affect the participant's ability to complete the study. * History of clinically significant multiple or severe drug allergies. * Have any clinically important abnormality at screening, as determined by investigator that could be detrimental to the participant, could compromise the study, or show evidence of other etiologies for dementia. * Screening magnetic resonance imaging (MRI) which shows evidence of significant abnormality that would suggest another potential etiology for progressive dementia or a clinically significant finding that may impact the participant's ability to safely participate in the study. * Have any contraindications for MRI or positron emission tomography (PET). * Have had prior treatment with a passive anti-amyloid immunotherapy. * Have received active immunization against Aβ in any other study. * Have known allergies to remternetug related compounds, or any components of the formulation.