Inclusion criteria: The main inclusion criteria include, but are not limited to, the following: * Has a clinical diagnosis of axial spondyloarthritis (axSpA) and meets the Assessment of SpondyloArthritis International Society (ASAS) classification criteria for axSpA, including ≥3 months of back pain with age at symptom onset <45 years * Meets the radiographic criteria of the modified New York criteria for ankylosing spondylitis (AS) as determined by the central reading at screening * Has active disease at screening and randomization * Has a history of inadequate response (IR)/intolerance to nonsteroidal anti-inflammatory drugs (NSAIDs) and has not received treatment with biologic disease-modifying antirheumatic drugs (bDMARDs), or has a history of IR/intolerance to up to a maximum of 2 classes of bDMARDs. Exclusion criteria: The main exclusion criteria include, but are not limited to, the following: * Has any arthritis with onset before age 17 or a current diagnosis of inflammatory joint disease other than radiographic axial spondyloarthritis (r-axSpA) (such as, but not limited to, rheumatoid arthritis, systemic lupus erythematosus, psoriatic arthritis (PsA), systemic sclerosis, myositis, etc.) or any other condition that, in the investigator's judgment, may interfere with the assessment of r-axSpA * Has a history of cancer (except for fully treated non-melanoma skin cancers or cervical carcinoma in situ after complete surgical excision) within the last 5 years * Has any active infection * Has any known allergies, hypersensitivity, or intolerance to tulisokibart or its excipients