This study is being conducted to look at the effect YB-101 has on thyroid function. This study will also evaluate how safe and well tolerated YB-101 is and how it is distributed through the body.

The study consists of a part 1, blinded treatment period, and a part 2 double-blinded treatment period. Participants will receive YB-101 or Placebo subcutaneously. Participants who participate in Part 1 can not participate in Part 2.

Participants will complete 34-39 in-clinic visits in Part 1 or Part 2 over an approximate 40 week period.

Inclusion Criteria:

• Have a documented diagnosis of Graves' Disease confirmed by the presence of thyroid-stimulating hormone receptor antibodies (TRAbs) by medical history or screening laboratory assessment
• Have a pre-existing diagnosis of TED or, conversely, no evidence of TED at the ophthalmological examination performed during screening
• Additional inclusion criteria are defined in the protocol

Exclusion Criteria:

• Previously treated with radioactive iodine (RAI) therapy or underwent total thyroidectomy
• Received any dose of levothyroxine, desiccated thyroid extract, or T3 within 6 weeks before screening
• Current treatment with teprotumumab or exposure to teprotumumab within 15 weeks prior to screening
• History of hyperthyroidism not caused by Graves' disease (eg. toxic adenoma, or toxic multinodular goiter) within 6 months before the screening visit
• Pregnant or lactating women
• Additional exclusion criteria are defined in the protocol