The goal of this clinical trial is to find out if the study drug will work as a new therapy for axSpA patients. This study is placebo-controlled, and evaluates if study drug can treat symptoms of axSpA, including global disease activity, pain, function and inflammation.

Researchers will compare vilamakitug to a placebo (no active drug) to see if the study drug works in axSpA patients to treat symptoms. Participants will take the assigned study treatment for 16 weeks for double blind period and potentially 12 weeks for open label extension.

Inclusion Criteria:

1. Male or female aged ≥18 and ≤65 years, with body weight >40 kg at screening, who are willing to provide informed consent, attend all clinic visits, comply with study-related procedures and able to understand and complete study-related questionnaires.
2. Must meet the ASAS-SPARTAN 2025 revised classification criteria for axial spondyloarthritis.
3. Active disease at screening, defined by BASDAI ≥ 4 and ASDAS-CRP ≥ 2.1
4. Participants should have received prior NSAIDs or have documented inadequate response to NSAIDs
5. Participants may be biological DMARD-naïve or have documented failure of no more than 1 prior biologic DMARD (≥12 weeks)

Exclusion Criteria:

1. History of treatment with vilamakitug
2. Any prior exposure to > 1 biologic DMARD
3. Any exposure to JAK or TYK2 inhibitors
4. Current drug or alcohol abuse or dependence, or a history of drug or alcohol abuse or dependence within a year prior to enrollment
5. Participation in another interventional clinical study within 30 days or 5 half-lives (whichever is longer) prior to enrollment, and during the study
6. Female participants who are pregnant or breastfeeding at screening, or who intend to become pregnant during the study or within 8 weeks after the last dose of investigational product (IP), and male participants who intend to father a child during the study or within 8 weeks after the last dose of IP.