Inclusion Criteria:

1. Participants must meet either one of the following criteria:

1. Randomized participant in protocol COG1201 and completed the study or
2. Referred by their treating physician to a participating COG1202 study site with a confirmed diagnosis of DLB, provide evidence of a historical MRI (within last 3 months) or CT-Scan (within last 3 months), a baseline Mini Mental Status Examination score (MMSE) of 18 - 27 inclusive and be approved by Sponsor
2. Participants must have caregiver(s) / study partner who in the opinion of the site principal investigator, has contact with the study participant for a sufficient number of hours per week to provide informative responses on the protocol assessments, oversee the administration of study drug, and willing and able to participate in study visits and some study assessments. The caregiver/ study partner must also provide informed consent to participate in the study.
3. Men or women 50- 86 years of age (inclusive).
4. Must have had no clinically relevant findings, other than change for progression of DLB, on historical MRI or CT scan.
5. In the opinion of the investigator, must be able to complete all protocol evaluations.

Exclusion Criteria:

1. If enrolled in the previous CT1812 clinical trial for DLB (COG1201), did not complete the clinical trial, or had an adverse event that could cause an undue risk, or progressed to severe DLB and cannot complete study assessments.
2. Any neurological condition that may be contributing to cognitive impairment and beyond those caused by the participant's DLB.
3. History of cancer within 3 years of screening with the exception of fully excised non-melanoma skin cancers or non-metastatic prostate cancer that has been stable for at least 6 months based on imaging or Prostate-Specific Antigen (PSA) levels.
4. Clinically significant, advanced or unstable disease that may interfere with outcome evaluations.
5. Any condition, which in the opinion of the investigator or the sponsor makes the participant unsuitable for inclusion.
6. No access to a Primary Care Physician, inability or unwillingness to have lab sample collection completed per protocol.

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 9/08/2025. Questions regarding updates should be directed to the study team contact.