SCHEDULE 13D/A 0000902664-25-004297 0001535978 XXXXXXXX LIVE 1 Common Stock, par value $0.001 per share 10/29/2025 false 0001785173 282559103 89bio, Inc.

655 MONTGOMERY STREET SUITE 1500 SAN FRANCISCO CA 94111

Robert Atchinson 617-867-2800 Adage Capital Partners GP, L.L.C. 200 Clarendon Street, 52nd Floor Boston MA 02116 0001535978 N Adage Capital Management, L.P. AF N DE 0.00 0.00 0.00 0.00 0.00 N 0 IA PN 0001403404 N Robert Atchinson AF N X1 0.00 0.00 0.00 0.00 0.00 N 0 IN HC 0001403413 N Phillip Gross AF N X1 0.00 0.00 0.00 0.00 0.00 N 0 IN HC Common Stock, par value $0.001 per share 89bio, Inc. 655 MONTGOMERY STREET SUITE 1500 SAN FRANCISCO CA 94111 This Amendment No. 1 ("Amendment No. 1") amends the statement on Schedule 13D filed with the Securities and Exchange Commission (the "SEC") on October 3, 2025 (the "Schedule 13D") relates to the shares of common stock, par value $0.001 per share (the "Common Stock"), of 89bio, Inc., a Delaware corporation (the "Issuer"). This Amendment No. 1 amends and restates Item 5 as set forth below. Capitalized terms used herein and not otherwise defined in this Amendment No. 1 have the meanings set forth in the Schedule 13D. This Amendment No. 1 is the final amendment to the Schedule 13D and constitutes an "exit filing" for the Reporting Persons. See rows (11) and (13) of the cover pages to this Schedule 13D for the aggregate number of shares of Common Stock and percentages of the shares of Common Stock beneficially owned by each of the Reporting Persons. See rows (7) through (10) of the cover pages to this Schedule 13D for the number of shares of Common Stock 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. The transactions in the shares of Common Stock since the filing of the Schedule 13D by the Reporting Persons, which were all in the open market, are set forth in Schedule A, and are incorporated herein by reference. In addition, on October 29, 2025, the Reporting Persons tendered all of their 13,097,587 shares of Common Stock into the tender offer pursuant to the Merger Agreement at an offer price of (i) $14.50 per share in cash, and (ii) one non-tradeable contingent value right per share, all as described in the Company's SEC filings. Not applicable. October 29, 2025 Adage Capital Management, L.P. /s/ Robert Atchinson 10/31/2025 Robert Atchinson /s/ Robert Atchinson 10/31/2025 Phillip Gross /s/ Phillip Gross 10/31/2025