X0202 SCHEDULE 13G/A 0000918923 XXXXXXXX LIVE 3 Common Stock, $0.0001 par value per share 03/31/2026 0001826457 Monte Rosa Therapeutics, Inc. 61225M102 321 HARRISON AVENUE SUITE 900 BOSTON MA 02118 Rule 13d-1(c) BIOTECHNOLOGY VALUE FUND L P a DE 0.00 2716569.00 0.00 2716569.00 2716569.00 N 3.4 PN BVF I GP LLC a DE 0.00 2716569.00 0.00 2716569.00 2716569.00 N 3.4 OO BIOTECHNOLOGY VALUE FUND II LP a DE 0.00 1986984.00 0.00 1986984.00 1986984.00 N 2.5 PN BVF II GP LLC a DE 0.00 1986984.00 0.00 1986984.00 1986984.00 N 2.5 OO Biotechnology Value Trading Fund OS LP a E9 0.00 306361.00 0.00 306361.00 306361.00 N 0.4 PN BVF Partners OS Ltd. a E9 0.00 306361.00 0.00 306361.00 306361.00 N 0.4 CO BVF GP HOLDINGS LLC a DE 0.00 4703553.00 0.00 4703553.00 4703553.00 N 5.8 OO BVF PARTNERS L P/IL a DE 0.00 5085886.00 0.00 5085886.00 5085886.00 N 6.3 IA PN BVF INC/IL a DE 0.00 5085886.00 0.00 5085886.00 5085886.00 N 6.3 CO LAMPERT MARK N a X1 0.00 5085886.00 0.00 5085886.00 5085886.00 N 6.3 IN Monte Rosa Therapeutics, Inc. Biotechnology Value Fund, L.P. ("BVF") BVF I GP LLC ("BVF GP") Biotechnology Value Fund II, L.P. ("BVF2") BVF II GP LLC ("BVF2 GP") Biotechnology Value Trading Fund OS LP ("Trading Fund OS") BVF Partners OS Ltd. ("Partners OS") BVF GP Holdings LLC ("BVF GPH") BVF Partners L.P. ("Partners") BVF Inc. Mark N. Lampert ("Mr. Lampert") Each of the foregoing is referred to as a "Reporting Person" and collectively as the "Reporting Persons." Biotechnology Value Fund, L.P. 44 Montgomery St., 40th Floor San Francisco, California 94104 BVF I GP LLC 44 Montgomery St., 40th Floor San Francisco, California 94104 Biotechnology Value Fund II, L.P. 44 Montgomery St., 40th Floor San Francisco, California 94104 BVF II GP LLC 44 Montgomery St., 40th Floor San Francisco, California 94104 Biotechnology Value Trading Fund OS LP PO Box 309 Ugland House Grand Cayman, KY1-1104 Cayman Islands BVF Partners OS Ltd. PO Box 309 Ugland House Grand Cayman, KY1-1104 Cayman Islands BVF GP Holdings LLC 44 Montgomery St., 40th Floor San Francisco, California 94104 BVF Partners L.P. 44 Montgomery St., 40th Floor San Francisco, California 94104 BVF Inc. 44 Montgomery St., 40th Floor San Francisco, California 94104 Mark N. Lampert 44 Montgomery St., 40th Floor San Francisco, California 94104 Biotechnology Value Fund, L.P. Delaware BVF I GP LLC Delaware Biotechnology Value Fund II, L.P. Delaware BVF II GP LLC Delaware Biotechnology Value Trading Fund OS LP Cayman Islands BVF Partners OS Ltd. Cayman Islands BVF GP Holdings LLC Delaware BVF Partners L.P. Delaware BVF Inc. Delaware Mark N. Lampert United States Y As of the close of business on March 31, 2026, the Reporting Persons and a certain Partners managed account (the "Partners Managed Account") held certain Pre-Funded Warrants (the "Pre-Funded Warrants") exercisable for an aggregate of 625,000 Shares. The Pre-Funded Warrants are exercisable at any time at an exercise price of $0.0001 per Share and do not expire. A holder of Pre-Funded Warrants will not be entitled to exercise any portion of such Pre-Funded Warrants that, upon giving effect to such exercise, would result in: (i) the aggregate number of Shares beneficially owned by such holder (together with its affiliates) to exceed 9.99% of the number of Shares outstanding immediately after giving effect to the exercise, or (ii) the combined voting power of the Issuer's securities beneficially owned by such holder (together with its affiliates) to exceed 9.99% of the combined voting power of all of the Issuer's securities then outstanding immediately after giving effect to the exercise (the "Pre-Funded Warrants Blocker"). As of the close of business on March 31, 2026, the Pre-Funded Warrants Blocker did not limit the exercise of any of the Pre-Funded Warrants held by the Reporting Persons and the Partners Managed Account. As of the close of business on March 31, 2026, (i) BVF beneficially owned 2,716,569 Shares, including 333,837 Shares underlying the Pre-Funded Warrants held by it, (ii) BVF2 beneficially owned 1,986,984 Shares, including 244,178 Shares underlying the Pre-Funded Warrants held by it, and (iii) Trading Fund OS beneficially owned 306,361 Shares, including 37,649 Shares underlying the Pre-Funded Warrants held by it. BVF GP, as the general partner of BVF, may be deemed to beneficially own the 2,716,569 Shares beneficially owned by BVF. BVF2 GP, as the general partner of BVF2, may be deemed to beneficially own the 1,986,984 Shares beneficially owned by BVF2. Partners OS, as the general partner of Trading Fund OS, may be deemed to beneficially own the 306,361 Shares beneficially owned by Trading Fund OS. BVF GPH, as the sole member of each of BVF GP and BVF2 GP, may be deemed to beneficially own the 4,703,553 Shares beneficially owned in the aggregate by BVF and BVF2. Partners, as the investment manager of BVF, BVF2 and Trading Fund OS, and the sole member of Partners OS, may be deemed to beneficially own the 5,085,886 Shares beneficially owned in the aggregate by BVF, BVF2 and Trading Fund OS and held in the Partners Managed Account, including 75,972 Shares held in the Partners Managed Account, which includes 9,336 Shares underlying the Pre-Funded Warrants held in the Partners Managed Account. BVF Inc., as the general partner of Partners, may be deemed to beneficially own the 5,085,886 Shares beneficially owned by Partners. Mr. Lampert, as a director and officer of BVF Inc., may be deemed to beneficially own the 5,085,886 Shares beneficially owned by BVF Inc. The foregoing should not be construed in and of itself as an admission by any Reporting Person as to beneficial ownership of any Shares owned by another Reporting Person. BVF GP disclaims beneficial ownership of the Shares beneficially owned by BVF. BVF2 GP disclaims beneficial ownership of the Shares beneficially owned by BVF2. Partners OS disclaims beneficial ownership of the Shares beneficially owned by Trading Fund OS. BVF GPH disclaims beneficial ownership of the Shares beneficially owned by BVF and BVF2. Each of Partners, BVF Inc. and Mr. Lampert disclaims beneficial ownership of the Shares beneficially owned by BVF, BVF2 and Trading Fund OS and held in the Partners Managed Account, and the filing of this statement shall not be construed as an admission that any such person or entity is the beneficial owner of any such securities. The following percentages are based upon a denominator that is the sum of (i) 80,015,667 Shares outstanding as of March 2, 2026, as disclosed in the Issuer's Annual Report on Form 10-K filed with the Securities and Exchange Commission on March 17, 2026, and (ii) certain or all of the 625,000 Shares underlying the Pre-Funded Warrants held by the Reporting Persons and the Partners Managed Account, as applicable. As of the close of business on March 31, 2026, (i) BVF beneficially owned approximately 3.4% of the outstanding Shares, (ii) BVF2 beneficially owned approximately 2.5% of the outstanding Shares, (iii) Trading Fund OS beneficially owned less than 1% of the outstanding Shares, (iv) BVF GP may be deemed to beneficially own approximately 3.4% of the outstanding Shares, (v) BVF2 GP may be deemed to beneficially own approximately 2.5% of the outstanding Shares, (vi) Partners OS may be deemed to beneficially own less than 1% of the outstanding Shares, (vii) BVF GPH may be deemed to beneficially own approximately 5.8% of the outstanding Shares, and (viii) each of Partners, BVF Inc. and Mr. Lampert may be deemed to beneficially own approximately 6.3% of the outstanding Shares (less than 1% of the outstanding Shares are held in the Partners Managed Account). See Cover Pages Items 5-9. See Cover Pages Items 5-9. See Cover Pages Items 5-9. See Cover Pages Items 5-9. Y N BVF GPH, Partners, BVF Inc. and Mr. Lampert share voting and dispositive power over the Shares beneficially owned by BVF and BVF2. Partners, BVF Inc. and Mr. Lampert share voting and dispositive power over the Shares beneficially owned by Trading Fund OS and held in the Partners Managed Account. Y N See Exhibit 99.1 to the Schedule 13G filed with the Securities and Exchange Commission on January 31, 2025. Y N By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11. BIOTECHNOLOGY VALUE FUND L P /s/ Mark N. Lampert 05/15/2026 BVF I GP LLC /s/ Mark N. Lampert 05/15/2026 BIOTECHNOLOGY VALUE FUND II LP /s/ Mark N. Lampert 05/15/2026 BVF II GP LLC /s/ Mark N. Lampert 05/15/2026 Biotechnology Value Trading Fund OS LP /s/ Mark N. Lampert 05/15/2026 BVF Partners OS Ltd. /s/ Mark N. Lampert 05/15/2026 BVF GP HOLDINGS LLC /s/ Mark N. Lampert 05/15/2026 BVF PARTNERS L P/IL /s/ Mark N. Lampert 05/15/2026 BVF INC/IL /s/ Mark N. Lampert 05/15/2026 LAMPERT MARK N /s/ Mark N. Lampert 05/15/2026