Key Inclusion criteria:
- Males and non-pregnant, non-lactating females
- Weight at screening as follows:
- Cohort 1 = ≥ 35 kg (≥ 77 lbs)
- Cohort 2 Group 1 = ≥ 25 kg (≥ 55 lbs)
- Cohort 2 Group 2 = ≥ 14 kg to < 25 kg (≥ 30 lbs to <55 lbs)
- Cohort 2 Group 3 = ≥ 10 kg to < 14 kg (≥ 22 lbs to < 30 lbs) or
- 14 kg to < 25 kg (≥ 30 lbs to < 55 lbs)
- Willing and able to provide written informed consent/assent (child and parent/legal guardian)
- Documented evidence of CHB (eg, HBsAg-positive for ≥ 6 months)
- HBeAg-positive, or HBeAg-negative, chronic HBV infection with all of the following:
- Screening HBV DNA ≥ 2 × 10^4 IU/mL
- Screening serum ALT > 45 U/L (> 1.5 × ULN: 30 U/L) and ≤ 10 × ULN (by central laboratory range)
- Treatment-naive or treatment-experienced will be eligible for enrollment.
- Estimated creatinine clearance (CLCr) ≥ 80 mL/min/1.73m^2 (using the Schwartz formula)
- Normal ECG
Key Exclusion criteria:
- Females who are pregnant or breastfeeding
- Males and females of reproductive potential who are unwilling to use an "effective", protocol-specified method(s) of contraception during the study.
- Coinfection with hepatitis C virus (HCV), HIV, or hepatitis D virus (HDV)
- Evidence of hepatocellular carcinoma (Note: if screening alpha-fetoprotein (AFP) is < 50 ng/mL no imaging study is needed; however, if the screening AFP is > 50 ng/mL an imaging study is required)
- Any history of, or current evidence of, clinical hepatic decompensation
- Abnormal hematological and biochemical parameters
- Chronic liver disease of non-HBV etiology (e.g., hemochromatosis, alpha-1 antitrypsin deficiency, cholangitis)
- Received solid organ or bone marrow transplant
- Currently receiving therapy with immunomodulators (eg, corticosteroids), or immunosuppressants
- Significant renal, cardiovascular, pulmonary, or neurological disease in the opinion of the Investigator
- Malignancy within the 5 years prior to screening. Individuals under evaluation for possible malignancy are not eligible.
- Current alcohol or substance abuse judged by the investigator to potentially interfere with subject compliance.
Note: Other protocol defined Inclusion/Exclusion criteria may apply.