X0202 SCHEDULE 13D/A 0001104659-23-112496 0001845105 XXXXXXXX LIVE 6 Ordinary Shares, par value EUR0.01 per share 07/02/2026 false 0001956827 00370M103 Abivax S.A.

7-11, boulevard Haussmann Paris I0 75009

Armance Bordes 33 1 76 23 41 09 7-11, boulevard Haussmann Paris I0 75009 John Partigan 202-585-8000 Nixon Peabody LLP 799 9 Street NW Ste 500 Washington DC 20001 0001845105 N Sofinnova Crossover I SLP b OO N I0 3535843.00 0.00 2474299.00 0.00 3535843.00 N 4.3 OO Note in relation to Items 7 and 8: Sofinnova Partners SAS, a French corporation ("SP SAS"), the management company of Sofinnova Crossover I SLP ("SC"), may be deemed to have sole voting power, and Antoine Papiernik ("Papiernik"), Cedric Moreau ("Moreau"), Kinam Hong ("Hong"), Joseph Anderson ("Anderson") and Jacques Theurillat ("Theurillat"), the members of the investment committee of SC, may be deemed to have shared power to vote these shares. Note in relation to Items 9 and 10: SP SAS, the management company of SC, may be deemed to have sole power to dispose of these shares, and Papiernik, Moreau, Hong, Anderson and Theurillat, the members of the investment committee of SC, may be deemed to have shared power to dispose of these shares. Note in relation to Items 8, 10, 11 and 13: The Reporting Person beneficially owns 2,474,299 Ordinary Shares (including ordinary shares represented by American depositary shares) and has 3,535,843 voting rights related to such shares. The aggregate amount beneficially owned and percent of class reported above are based on the Reporting Person's voting rights and the 82,130,598 voting rights outstanding as of May 31, 2026. 0001574139 N Sofinnova Partners SAS b OO N I0 3535843.00 0.00 2474299.00 0.00 3535843.00 N 4.3 OO Note in relation to Items 7 and 8: SP SAS, the management company of SC, may be deemed to have sole voting power, and Papiernik, Moreau, Hong, Anderson and Theurillat, the members of the investment committee of SC, may be deemed to have shared power to vote these shares. Note in relation to Items 9 and 10: SP SAS, the management company of SC, may be deemed to have sole power to dispose of these shares, and Papiernik, Moreau, Hong, Anderson and Theurillat, the members of the investment committee of SC, may be deemed to have shared power to dispose of these shares. Note in relation to Items 8, 10, 11 and 13: The Reporting Person beneficially owns 2,474,299 Ordinary Shares (including ordinary shares represented by American depositary shares) and has 3,535,843 voting rights related to such shares. The aggregate amount beneficially owned and percent of class reported above are based on the Reporting Person's voting rights and the 82,130,598 voting rights outstanding as of May 31, 2026. 0001768408 N Antoine Papiernik b OO N I0 3535843.00 0.00 2474299.00 0.00 3535843.00 N 4.3 IN Note to Items 7 and 8: SP SAS, the management company of SC, may be deemed to have sole voting power, and Papiernik, a member of the investment committee of SC, may be deemed to have shared power to vote these shares. Note to Items 9 and 10: SP SAS, the management company of SC, may be deemed to have sole power to dispose of these shares, and Papiernik, a member of the investment committee of SC, may be deemed to have shared power to dispose of these shares. Note in relation to Items 8, 10, 11 and 13: The Reporting Person beneficially owns 2,474,299 Ordinary Shares (including ordinary shares represented by American depositary shares) and has 3,535,843 voting rights related to such shares. The aggregate amount beneficially owned and percent of class reported above are based on the Reporting Person's voting rights and the 82,130,598 voting rights outstanding as of May 31, 2026. Y Cedric Moreau b OO N I0 3535843.00 0.00 2474299.00 0.00 3535843.00 N 4.3 IN Note to Items 7 and 8: SP SAS, the management company of SC, may be deemed to have sole voting power, and Moreau, a member of the investment committee of SC, may be deemed to have shared power to vote these shares. Note to Items 9 and 10: SP SAS, the management company of SC, may be deemed to have sole power to dispose of these shares, and Moreau, a member of the investment committee of SC, may be deemed to have shared power to dispose of these shares. Note in relation to Items 8, 10, 11 and 13: The Reporting Person beneficially owns 2,474,299 Ordinary Shares (including ordinary shares represented by American depositary shares) and has 3,535,843 voting rights related to such shares. The aggregate amount beneficially owned and percent of class reported above are based on the Reporting Person's voting rights and the 82,130,598 voting rights outstanding as of May 31, 2026. Y Kinam Hong b OO N X1 3535843.00 0.00 2474299.00 0.00 3535843.00 N 4.3 IN Note to Items 7 and 8: SP SAS, the management company of SC, may be deemed to have sole voting power, and Hong, a member of the investment committee of SC, may be deemed to have shared power to vote these shares. Note to Items 9 and 10: SP SAS, the management company of SC, may be deemed to have sole power to dispose of these shares, and Hong, a member of the investment committee of SC, may be deemed to have shared power to dispose of these shares. Note in relation to Items 8, 10, 11 and 13: The Reporting Person beneficially owns 2,474,299 Ordinary Shares (including ordinary shares represented by American depositary shares) and has 3,535,843 voting rights related to such shares. The aggregate amount beneficially owned and percent of class reported above are based on the Reporting Person's voting rights and the 82,130,598 voting rights outstanding as of May 31, 2026. Y Joseph Anderson b OO N X0 3535843.00 0.00 2474299.00 0.00 3535843.00 N 4.3 IN Note to Items 7 and 8: SP SAS, the management company of SC, may be deemed to have sole voting power, and Anderson, a member of the investment committee of SC, may be deemed to have shared power to vote these shares. Note to Items 9 and 10: SP SAS, the management company of SC, may be deemed to have sole power to dispose of these shares, and Anderson, a member of the investment committee of SC, may be deemed to have shared power to dispose of these shares. Note in relation to Items 8, 10, 11 and 13: The Reporting Person beneficially owns 2,474,299 Ordinary Shares (including ordinary shares represented by American depositary shares) and has 3,535,843 voting rights related to such shares. The aggregate amount beneficially owned and percent of class reported above are based on the Reporting Person's voting rights and the 82,130,598 voting rights outstanding as of May 31, 2026. Y Jacques Theurillat b OO N V8 3535843.00 0.00 2474299.00 0.00 3535843.00 N 4.3 IN Note to Items 7 and 8: SP SAS, the management company of SC, may be deemed to have sole voting power, and Theurillat, a member of the investment committee of SC, may be deemed to have shared power to vote these shares. Note to Items 9 and 10: SP SAS, the management company of SC, may be deemed to have sole power to dispose of these shares, and Theurillat, a member of the investment committee of SC, may be deemed to have shared power to dispose of these shares. Note in relation to Items 8, 10, 11 and 13: The Reporting Person beneficially owns 2,474,299 Ordinary Shares (including ordinary shares represented by American depositary shares) and has 3,535,843 voting rights related to such shares. The aggregate amount beneficially owned and percent of class reported above are based on the Reporting Person's voting rights and the 82,130,598 voting rights outstanding as of May 31, 2026. Ordinary Shares, par value EUR0.01 per share Abivax S.A. 7-11, boulevard Haussmann Paris I0 75009 Introductory Statement: This Amendment No. 6 (this "Amendment"), being filed by Sofinnova Crossover I SLP ("SC"), Sofinnova Partners SAS, a French corporation ("SP SAS"), Antoine Papiernik ("Papiernik"), Cedric Moreau ("Moreau"), Kinam Hong ("Hong"), Joseph Anderson ("Anderson") and Jacques Theurillat ("Theurillat") the members of the investment committee of SC (collectively, the "Listed Persons" and together with SC and SP SAS, the "Reporting Persons"), amends and supplements the Schedule 13D filed with the Securities and Exchange Commission (the "SEC") on October 30, 2023, as amended by Amendment No. 1, filed with the SEC on February 14, 2025, as further amended by Amendment No. 2, filed with the SEC on July 31, 2025, as amended by Amendment No. 3, filed with the SEC on October 30, 2025, as further amended by Amendment No. 4, filed with the SEC on January 14, 2026, and as further amended by Amendment No. 5, filed with the SEC on May 11, 2026 (collectively, as amended, the "Schedule 13D"). This Schedule 13D relates to the Ordinary Shares, par value EUR0.01 per share (the "Ordinary Shares"), including ordinary shares represented by American Depositary Shares ("ADS"), of Abivax SA, a societe anonyme incorporated under the laws of the French Republic (the "Issuer"). Except as specifically provided herein, this Amendment No. 6 does not modify any of the information previously reported in the Schedule 13D. Capitalized terms used herein shall have the meanings ascribed to them in the Schedule 13D. During the last five years, none of the Reporting Persons has been convicted in any criminal proceeding (excluding traffic violations or similar misdemeanors). During the last five years, none of the Reporting Persons has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws. Item 4 of the Schedule 13D is hereby amended and supplemented as follows: SC sold the amounts of ADS and Ordinary Shares on the date and at the prices set forth below in open market transactions on NASDAQ and Euronext. All daily sales of the shares were sold in multiple transactions at varying prices. The Reporting Persons undertake to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each weighted average price set forth in this Schedule 13D. June 30, 2026: -500,000 ADSs at a weighted average price of $132.7347 per share. July 1, 2026: -25,000 ADSs at a weighted average price of $134.2377 per share. July 2, 2026: -275,000 ADSs at a weighted average price of $140.9365 per share.* -35,469 Ordinary Shares at a weighted average price of $144.2752 per share.* July 3, 2026: -25,000 Ordinary Shares at a weighted average price of $156.2041 per share.* -39,531 Ordinary Shares at a weighted average price of $155.0654 per share.* July 6, 2026: -3,195 Ordinary Shares at a weighted average price of $155.0436 per share.* * Transaction completed in Euros. Price per share converted to USD at an exchange rate of $1.1448 as of July 3, 2026. All of the Ordinary Shares that are held of record by the Reporting Persons as reported herein were acquired for investment purposes. The Reporting Persons retain the right to change their investment intent, from time to time to acquire additional Ordinary Shares or other securities of the Issuer, or to sell or otherwise dispose of all or part of the Ordinary Shares or other securities of the Issuer, if any, beneficially owned by them, in any manner permitted by law. The Reporting Persons may engage from time to time in ordinary course transactions with financial institutions with respect to the securities described herein. Except as set forth above, none of the Reporting Persons currently has any plans or proposals which would be related to or would result in any of the matters described in Items 4(a)-(j) of the Instructions to Schedule 13D. However, as part of the ongoing evaluation of investment and investment alternatives, the Reporting Persons may consider such matters and, subject to applicable law, may formulate a plan with respect to such matters, and, from time to time, may hold discussions with or make formal proposals to management or the board of directors of the Issuer or other third parties regarding such matters. Item 5(a) of the Schedule 13D is hereby amended and supplemented as follows: As of July 6, 2026, SC held directly 2,474,299 Ordinary Shares representing approximately 3.1% of the Issuer's outstanding Ordinary Shares and 3,535,843 voting rights representing approximately 4.3% of the Issuer's outstanding voting rights. None of the other Reporting Persons hold any Ordinary Shares or ADSs directly. SP SAS is the management company of SC and may be deemed to have shared voting and investment control over the Ordinary Shares and ADSs held by SC. Each of Antoine Papiernik, Cedric Moreau, Kinam Hong, Joseph Anderson and Jacques Theurillat are the members of the investment committee of SC and may be deemed to have shared voting and investment control over the Ordinary Shares and ADSs held by SC. Each of such individuals disclaims beneficial ownership of such Ordinary Shares and ADSs except to the extent of their pecuniary interest therein. The ownership percentages are based upon 79,782,941 of the Issuer's Ordinary Shares outstanding as of May 31, 2026. The voting percentages are based upon 82,130,598 voting rights outstanding as of May 31, 2026. Item 5(b) of the Schedule 13D is hereby amended and supplemented as follows: See the information contained on the cover pages of this Amendment, which is incorporated herein by reference. Item 5(c) of the Schedule 13D is hereby amended and supplemented as follows: Except as disclosed herein, there have been no other reportable transactions with respect to the Ordinary Shares or ADSs of the Issuer within the last 60 days by the Reporting Persons. EX 99.1 - Agreement regarding filing of joint Schedule 13D (incorporated by reference from Exhibit 99.1 to Schedule 13D filed by the Reporting Persons on October 30, 2023) Sofinnova Crossover I SLP /s/ Antoine Papiernik 07/06/2026 Sofinnova Partners SAS /s/ Antoine Papiernik 07/06/2026 Antoine Papiernik /s/ Antoine Papiernik 07/06/2026 Cedric Moreau /s/ Cedric Moreau 07/06/2026 Kinam Hong /s/ Kinam Hong 07/06/2026 Joseph Anderson /s/ Joseph Anderson 07/06/2026 Jacques Theurillat /s/ Jacques Theurillat 07/06/2026