A Phase 1 Trial of AMG 691 in Healthy Chinese and Japanese Volunteers

Inclusion Criteria: * Healthy male or female participants, 18 to 60 years of age. * First-generation Chinese ancestry (born in China, Hong Kong, Taiwan, or Macau with 2 Chinese parents and 4 Chinese grandparents) or first-generation Japanese ancestry (born in Japan with 2 Japanese parents and 4 Japanese grandparents). * Body mass index (BMI) 18.0 to 30.0 kg/m\^2 (inclusive) and body weight ≥40 kg. * In good general health based on medical history, physical examination, vital signs, electrocardiogram (ECG), and clinical laboratory evaluations. * Female participants must not be pregnant or breastfeeding. * Participants of reproductive potential must agree to follow protocol-specified contraception requirements. * Willing to maintain usual diet and physical activity regimen throughout study participation. Exclusion Criteria: * Clinically significant medical condition, disease, or abnormal finding that could interfere with study participation or interpretation of results. * Clinically significant ECG abnormalities * Clinically significant abnormal blood pressure or pulse rate at screening/check-in. * History of malignancy (except adequately treated in situ cervical cancer or non-melanoma skin cancer \>5 years before dosing). * Deep vein thrombosis or pulmonary embolism within 3 months prior to check-in. * History of hypersensitivity/anaphylaxis to biologic therapies, mammalian-derived products, or AMG 691 excipients. * Active, chronic, recurrent, or unresolved infection; history of severe infection requiring intravenous (IV) antibiotics within the past 3 years. * Positive or indeterminate QuantiFERON-TB Gold test. * Untreated or unresolved helminth parasitic infection. * History of immunodeficiency. * Receipt of live or live-attenuated vaccines within 12 weeks before check-in or planned during the study. * Estimated glomerular filtration rate (eGFR) \<70 mL/min/1.73 m\^2. * Alanine Aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, or direct bilirubin \>1.5 × Upper Limit Normal (ULN). * Positive screening tests for human immunodeficiency virus (HIV), hepatitis B, or hepatitis C infection. Hepatitis B serology consistent with prior vaccination is permitted. * Use of prohibited prescription, over-the-counter, herbal, vitamin, or dietary supplement products within 30 days (or 5 half-lives) before enrollment, unless approved by the investigator. * History of illicit drug use within 1 year, positive drug screen, or unwillingness to abstain from illicit drugs/cannabinoids during the study. * Use of tobacco or nicotine-containing products within 6 months prior to check-in. * History of alcohol abuse or excessive alcohol consumption. * History of non-suicidal self-injury within 5 years or unstable major depressive disorder/other severe psychiatric disorder within 2 years. * Participation in another investigational drug study within 90 days (or 5 half-lives) prior to check-in. * Previous exposure to AMG 691. * Recent donation of blood, plasma, or platelets. * Any participant considered unsuitable by the investigator or unwilling to comply with study restrictions.