Inclusion criteria: 1. Have completed the study treatment in FXS6837-IIb-201, and are evaluated by the investigator to have an anticipated benefit exceeding risk with long-term FXS6837 treatment; 2. eGFR (CKD-EPI) ≥ 30 mL/min/1.73 m2 at screening; 3. Vaccinated against Neisseria meningitidis and Streptococcus pneumoniae as required by the previous study (Booster vaccination should be administered promptly in accordance with vaccination guidelines and local immunization authority requirements if the vaccine protection period fails to cover the treatment duration of this study); 4. Able to continue optimized treatment with RASi, SGLT2i, ERA, and hydroxychloroquine throughout the study with stable prescribed dosing; 5. Have a detailed understanding of the nature, significance, possible benefits, potential inconveniences, and potential risks of the trial, and voluntarily participate in this clinical trial; Able to communicate well with the investigators and comply with the requirements of the entire study; And signed a written ICF; 6. Participants of reproductive potential commit to having no plans for pregnancy or sperm/egg donation from screening until 1 month (female participants) or 3 months (male participants) after the last dose and voluntarily take effective physical contraceptive methods (including partners). Exclusion criteria: 1. Known or suspected by investigators to have immunodeficiency diseases or hereditary complement deficiency; 2. Any organ transplant recipients (except corneal transplant); 3. Concomitant major systemic diseases, including but not limited to: advanced heart disease (such as NYHA class IV), severe pulmonary disease (such as severe pulmonary hypertension [WHO class IV]), active hepatitis, or other major systemic diseases assessed by investigators as unable to participate in this study; 4. History of malignant tumors within 5 years before screening (except carcinoma in situ and thyroid cancer assessed by investigators as curatively resected).

5. Previous history of Neisseria meningitidis or recurrent Streptococcus pneumoniae infection ; 6. Suspected or known history of allergies to similar ingredients of the study drug or any ingredient in the study drug; 7. Pregnant or lactating women or those with positive pregnancy test results; 8. Other conditions deemed by the investigator that may potentially interfere with study conduct, impose additional risks to the participant, or render the individual ineligible for study participation.