This is a randomized, double-blind, placebo-controlled, multicenter Phase 3 study that will enroll approximately 330 subjects aged 12 to 75 years old with moderate to severe atopic dermatitis.

This study consists of a screening period followed by a placebo-controlled treatment period and then an extension treatment period and completed after a follow-up period after the completion of active treatment.

Inclusion Criteria:

1. Male or female subjects must be at least at ≥12 and ≤75 years of age and body weight ≥40 kg
2. Subject has a diagnosis of atopic dermatitis for at least 1 year.
3. Meets all of the following disease activity criteria: BSA ≥10% of AD involvement. EASI ≥16. IGA ≥3. WI-NRS ≥4
4. Subject has a recent history (within 6 months before the screening visit) of inadequate response or inability to tolerate topical AD treatments (TCS or TCI) or who have required systemic treatments for control of their disease.
5. Are willing to discontinue certain treatments for eczema (such as systemic and topical treatments during a washout period).

Exclusion Criteria:

1. Medical history including thrombocytopenia, coagulopathy or platelet dysfunction, malignancies, current or history of certain infections, lymphoproliferative disorders and other medical conditions at the discretion of the investigator.
2. Have received certain treatments that are contraindicated.
3. Subject currently has been diagnosed and has active forms of other inflammatory skin disease (e.g., psoriasis, or lupus erythematosus) that would interfere with the evaluation of atopic dermatitis or response to treatment.
4. Other active non-AD inflammatory skin diseases or conditions affecting skin
5. Subject with active/severe concomitant disease (s)/symptom(s) that requires administering of systemic corticosteroids or otherwise interferes with study participation or requires active frequent monitoring (e.g., unstable chronic asthma).
6. Acute or chronic medical or laboratory abnormality that may increase the risk associated with study participation.
7. Medical history including thrombocytopenia, coagulopathy or platelet dysfunction, malignancies, current or history of certain infections, lymphoproliferative disorders and other medical conditions at the discretion of the investigator.
8. Unwilling to discontinue current AD medications prior to the study or require treatment with prohibited medications during the study
9. Subject has any malignancies or has a history of malignancies with the exception of adequately treated or excised non-metastatic basal cell or squamous cell cancer of the skin, or cervical carcinoma in situ.
10. Pregnant or breastfeeding women, or women of childbearing potential who are unwilling to use contraception.
11. Subject has a previously received systemic JAK inhibitors
12. Unwilling to discontinue current AD medications prior to the study or require treatment with prohibited medications during the study