Inclusion criteria:
• Are ≥18 years of age at screening.
• Have a clinical diagnosis of TED associated with active, moderate to severe TED with the following at screening and Visit 0:
• A CAS ≥ 4 in either eye, and
• Clinical evidence of worsened proptosis with: 1. Proptosis ≥ 18 mm and/or 2. Proptosis ≥ 3 mm increase from participant's baseline (prior to diagnosis of TED), as estimated by the Investigator/assessor
• Have moderate to severe active TED, as defined by European Group on Graves' Orbitopathy (EUGOGO) guidelines.
• Have onset of active TED within 12 months prior to screening.
• Have documented evidence of detectable anti-TSHR-Ab at screening.
• Are not expected to require immediate surgical intervention and are not planning corrective surgery/irradiation or medical therapy for TED during the course of the study.
• Are euthyroid with the baseline disease under control or have mild hypo- or hyperthyroidism. Additional inclusion criteria are defined in the protocol. Exclusion criteria:
• Have decreased best corrected visual acuity due to optic neuropathy.
• Have at least a 2-point decrease in CAS or ≥2 mm decrease in proptosis between screening and Baseline assessments in either eye.
• Have used any steroid (intravenous or oral) for the treatment of TED or other conditions within 4 weeks prior to screening.
• Have used any steroid (Intravenous or oral) with a cumulative dose equivalent to ≥ 1 g of methylprednisolone for the treatment of TED.
• Have known autoimmune disease other than TED, that, in the opinion of the Investigator, would interfere with the course and conduct of the study.
• Had previous orbital irradiation or surgery for TED. Additional exclusion criteria are defined in the protocol.