Long-term Extension Study of Ulviprubart (ABC008) in Subjects With Inclusion Body Myositis

ABC008-IBM-202 is an open-label, multicenter study to evaluate the safety and efficacy of long-term administration of ulviprubart (ABC008) in subjects with IBM who have completed either Study ABC008-IBM-101 or Study ABC008-IBM-201. Subjects may be enrolled in this study if they meet study eligibility criteria and: * Have completed the Part 2 (Multiple Ascending Dose \[MAD\]) End of-Treatment (EOT) Visit in Study ABC008-IBM-101; subjects who continued further on into Part 3 of the study (MAD Extension) prior to enrolling in this study are also eligible; OR * Have completed the Week 80 Follow-up Visit in Study ABC008-IBM-201. Subjects will enter this study following their initial study such that dosing continues every eight weeks (Q8W) between the last dose in the initial study and the first dose in this long-term extension (LTE) Study IBM-202. Study subjects will continue to receive any ongoing concomitant medications from the initial study. Subjects will be required to sign an informed consent form before undertaking any study-specific procedures or assessments. Screening is intended to be done at the final visit of the initial study, which will coincide with the Baseline (Day 1) Visit for this study; if this is not possible, the Baseline (Day 1) Visit for this study, including screening, may be conducted at a separate visit (provided it occurs within the visit window defined in Appendix 1 of the protocol). Subsequent study visits will occur every eight weeks until EOT at Week 156, or withdrawal from the study.