X0202 SCHEDULE 13D/A 0000902664-20-003304 0001762304 XXXXXXXX LIVE 6 Ordinary Shares, par value $0.0001 per share 11/05/2026 false 0001778016 44975P103 NovaBridge Biosciences

SUITE 400, 2440 RESEARCH BLVD ROCKVILLE MD 20850

Richard A. Hornung 656-603-0860 Office #122, Windward 3 Building Regatta Office Park, West Bay Road Grand Cayman E9 KY1-9006 Adriana Schwartz 212-574-1200 Seward & Kissel LLP One Battery Park Plaza New York NY 10004 0001762304 N HHLR Advisors, Ltd. AF N E9 0.00 13295306.00 0.00 13295306.00 13295306.00 N 4.9 IA Consists of 5,780,568 ADSs representing 13,295,306 Ordinary Shares held by funds managed by HHLR. HHLR and HIM are under common control and share certain policies, personnel and resources. 0001510589 N Hillhouse Investment Management, Ltd. AF N E9 0.00 13295306.00 0.00 13295306.00 13295306.00 N 4.9 IA Consists of 5,780,568 ADSs representing 13,295,306 Ordinary Shares held by funds managed by HHLR. HHLR and HIM are under common control and share certain policies, personnel and resources. Ordinary Shares, par value $0.0001 per share NovaBridge Biosciences SUITE 400, 2440 RESEARCH BLVD ROCKVILLE MD 20850 This Amendment No. 6 ("Amendment No. 6") amends the statement on Schedule 13D filed with the Securities and Exchange Commission (the "SEC") on September 14, 2020, as amended by Amendment No. 1 filed on December 21, 2021 with the SEC, Amendment No. 2 filed on March 25, 2021 with the SEC, Amendment No. 3 filed on June 24, 2021 with the SEC, Amendment No. 4 filed on September 27, 2021 with the SEC, Amendment No. 5 filed on June 30, 2023 with the SEC, and as amended hereby (the "Schedule 13D"), with respect to the ordinary shares, par value $0.0001 per share (the "Ordinary Shares") of NovaBridge Biosciences (f/k/a I-MAB), an exempted Cayman Islands company (the "Issuer"). Capitalized terms used herein and not otherwise defined in this Amendment No. 6 have the meanings set forth in the Schedule 13D. This Amendment No. 6 amends Items 5(a)-(c) and (e) as set forth below. This Amendment No. 6 is the final amendment to the Schedule 13D and constitutes an "exit filing" for each of the Reporting Persons. There is no CUSIP number assigned to the Ordinary Shares. CUSIP number 44975P103 has been assigned to the American Depositary Shares ("ADSs") of the Issuer, which are quoted on the Nasdaq Global Market under the symbol "NBP." Each 10 ADSs represents 23 Ordinary Shares. See rows (11) and (13) of the cover pages to this Schedule 13D for the aggregate number of Ordinary Shares and percentages of the Ordinary Shares beneficially owned by each Reporting Person. The percentage used in this Schedule 13D is calculated based upon 270,740,383 Ordinary Shares outstanding as of July 27, 2026, as reported in the Issuer's Report of Foreign Private Issuer on Form 6-K filed with the SEC on September 8, 2026. See rows (7) through (10) of the cover pages to this Schedule 13D for the number of Ordinary Shares as to which each Reporting Person has the sole or shared power to vote or direct the vote and sole or shared power to dispose or to direct the disposition. Information concerning transactions in the Ordinary Shares (which were in the form of ADS) effected by the Reporting Persons in the last 60 days is set forth in Annex A hereto and is incorporated herein by reference. November 5, 2026 HHLR Advisors, Ltd. /s/ Audrey Woon 11/05/2026 Hillhouse Investment Management, Ltd. /s/ Audrey Woon 11/05/2026