This study is researching 2 different experimental drugs called REGN7508 and REGN9933. The study is focused on people who have Peripheral Artery Disease (PAD), which means that the blood vessels in their arms and legs have become too narrow. People with PAD have a higher risk of getting blood clots after procedures like Lower Extremity Revascularization (LER), a procedure to improve blood flow in the legs and feet.

The aim of this study is to see how well REGN7508 and REGN9933 prevent life-threatening blood clots in participants with PAD who have recently had LER. The effects of REGN7508 and REGN9933, individually, will also be compared to rivaroxaban and a placebo.

The study is looking at several other research questions, including:

• What side effects might happen from taking the study drugs and how do they compare to the side effects of rivaroxaban
• How much study drug is in the blood at different times
• Whether the body makes antibodies against the study drugs (which could make the drugs less effective or could lead to side effects)
• If the study drugs affect the ability of the blood to clot normally

Key Inclusion Criteria:

1. Successful LER distal to the external iliac artery for ischemia due to atherosclerotic disease within 10 days prior to randomization as described in the protocol

2. At least 1 of the following enrichment factors for major thrombotic vascular events:

   1. Bypass with prosthetic graft
   2. Endovascular treatment with stenting
   3. Target lesion length >15 cm
   4. History of LER or amputation for PAD prior to qualifying LER
   5. Type 2 diabetes mellitus requiring pharmacologic treatment
   6. Comorbid symptomatic coronary artery disease as described in the protocol
   7. Chronic kidney disease as described in the protocol
   8. Age ≥75 years

Key Exclusion Criteria:

1. Has any active clinical condition requiring chronic therapeutic anticoagulation after the index revascularization including known triple positive antiphospholipid syndrome
2. Has known bleeding diathesis, platelet count <50,000/mm^3 or history of non-traumatic intracerebral hemorrhage, known cerebral amyloid angiopathy, or known unrepaired cerebrovascular malformations
3. Has recent coronary revascularization as described in the protocol
4. For Cohort 2 only: Has estimated Glomerular Filtration Rate (eGFR) <15 mL/min/1.73m^2 within 14 days prior to randomization or on dialysis or expected to be started on dialysis within the next 12 weeks starting from randomization
5. Has any other condition or therapy which would make the participant unsuitable for this study or not allow participation for the full planned study period
6. Has allergy, hypersensitivity, or other contraindication to REGN7508, REGN9933, or rivaroxaban (Cohort 2 only) or their excipients

Note: Other Protocol Defined Inclusion/ Exclusion Criteria Apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing.

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry)
• the legal authority to share the data, and
• ensured the ability to protect participant privacy

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf

Cohort 1 of this study is double-blinded, and for Cohort 2 the participants, sponsor, and the investigators will be blinded to REGN7508 or REGN9933, but rivaroxaban will be administered as open-label.