A Study to Evaluate the Pharmacokinetics, Pharmacodynamics, Safety and Tolerability of Inebilizumab in Children With Generalized Myasthenia Gravis (gMG)

Inclusion Criteria * Participant's legally authorized representative has provided informed consent when the participant is legally too young to provide informed consent and the participant has provided written assent based on local regulations and/or guidelines before any study-specific activities/procedures being initiated. * Age ≥ 2 to \< 18 years of age on the day of enrollment. * Diagnosis of gMG defined as: * Positive serologic test for anti-acetylcholine receptor (AChR) or anti-muscle-specific tyrosine kinase (MuSK) antibody (Ab) titers as confirmed at screening (1 retest allowed), and * At least 1 of the following: * History of abnormal neuromuscular transmission test results demonstrated by single-fiber electromyography or repetitive nerve stimulation; or * History of positive anticholinesterase test (eg, edrophonium chloride test); or * Participant demonstrated improvement in gMG signs on oral cholinesterase inhibitors, as assessed by the treating physician; or * Clinical syndrome consistent with a diagnosis of gMG, and not otherwise explained by another condition. * Myasthenia Gravis Foundation of America Clinical Classification Class II, III, or IV at the time of screening. * Participants must be on: * Corticosteroids only, with no dose increase within 4 weeks prior to screening, or * One allowed non-steroidal immunosuppressive therapies (IST) (azathioprine, mycophenolate mofetil, or mycophenolic acid) with continuous use for at least 6 months prior to screening and no dose increase within 4 months prior to screening, or * Combination of (1) corticosteroids with no dose increase within 4 weeks prior to screening and (2) one allowed non-steroidal IST with continuous use for at least 6 months prior to screening and no dose increase within 4 months prior to screening. Tacrolimus is allowed in Japan only, with continued use for ≥ 6 months prior to screening and no dose increase within 4 months prior to screening. * Participants may enter the study on a stable dose of acetylcholinesterase inhibitors (pyridostigmine dose). The acetylcholinesterase inhibitor dose must have been stable for at least 2 weeks prior to enrollment. * Vital signs and laboratory parameters within the normal ranges at screening, or, if outside normal ranges, deemed not clinically significant by the investigator. Exclusion Criteria * Employees of the Sponsor, contract research organization (CRO), site staff, and their family members. * Thymectomy within 12 months prior to baseline (Day 1) visit or planned thymectomy during the duration of the treatment period. * Unresected thymoma- Participants with benign thymoma resected \> 12 months prior to screening may enroll. * History of recurrent significant infections. * Known immunodeficiency disorder, including current infection or positive test for human immunodeficiency virus (HIV). * Positive test for chronic hepatitis B infection at screening. * History of untreated hepatitis C infection, or positive antibody test for hepatitis C virus (HCV). * History of active or latent tuberculosis (TB), or a positive QuantiFERON®-TB Gold test at screening, unless treatment for TB was completed per local guidelines. * History of progressive multifocal leukoencephalopathy. * Participants diagnosed with congenital myasthenic syndromes. * Receipt of any biologic B-cell-depleting therapy (eg, rituximab, ocrelizumab, obinutuzumab, ofatumumab, inebilizumab) or any experimental B-cell-depleting agent in the 6 months prior to screening. * Receipt of any other monoclonal antibody (mAb) or large molecule biologic, including but not limited to FcRn inhibitors, anti-TNF mAbs, anti-janus kinase (JAK) Stat mAbs, and complement inhibitors within 6 months prior to screening. * Receipt of the following medications or treatments at any time prior to randomization: alemtuzumab, total lymphoid irradiation, bone marrow transplant, T-cell vaccination therapy, natalizumab. * Participants who are pregnant or breastfeeding or planning to get pregnant.