The goal of this observational study is to learn about the HBsAg reversion rate at 48 weeks off treatment in HBsAg-negative patients by HBsAg NEXT assay which has improved sensitivity compared to current ARCHITECT HBsAg Assay. The main question it aims to answer is: What's the HBsAg reversion rate at 48 weeks off treatment in HBsAg-negative patients by HBsAg NEXT assay? HBsAg NEXT assay technology (lower limit of detection for HBsAg is 0.005 IU/ml) and current ARCHITECT HBsAg assay (lower limit of detection for HBsAg is 0.05 IU/ml) are applied for HBsAg detection in patients achieving functional cure, and to compare the difference in HBsAg reversion rate 48 weeks off treatment under the two types of criteria.