A Study to Understand How the Study Medicine Dazukibart Works in People With Idiopathic Inflammatory Myopathies

Inclusion Criteria: * Participants that completed a qualifying study through Week 52. Exclusion Criteria: * Any medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation. * Previous administration with an investigational product (drug or vaccine) other than dazukibart in a qualifying study within 30 days (or as determined by the local requirement) or 5 half-lives preceding baseline in this study (whichever is longer). * Current use of any prohibited concomitant medication(s). * Active bacterial, viral, fungal, mycobacterial or other infections. * Ongoing adverse event in a qualifying study or the participant has met safety monitoring criteria in a qualifying study that have not resolved. * Investigator site staff or sponsor employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.