The purpose of this study is to measure the difference in time to developing or worsening memory, thinking, or functional problems due to Alzheimer's disease occurring in participants receiving study drug compared to placebo.

Participation could last up to 255 weeks including screening, a double-blind treatment period, and a double-blind observation period. In addition, eligible participants who receive placebo during the double-blind treatment period may choose to extend their study participation to receive open-label remternetug in an extension period.

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.

Anonymized individual patient level data will be provided in a secure access environment upon approval of a research proposal and a signed data sharing agreement.

Data are available 6 months after the primary publication and approval of the indication studied in the US and EU, whichever is later. Data will be indefinitely available for requesting.

A research proposal must be approved by an independent review panel and researchers must sign a data sharing agreement.