Sec Form 4 Filing - BAKER BROS. ADVISORS LP @ IGM Biosciences, Inc. - 2025-08-14

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person BAKER BROS. ADVISORS LP 2. Issuer Name and Ticker or Trading Symbol IGM Biosciences, Inc. [ IGMS] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner _____ Officer (give title below) X __ Other (specify below) Former 10% owner and director (Last) (First) (Middle) 860 WASHINGTON STREET, 3RD FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 08/14/2025 (Street) NEW YORK, NY10014 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 08/14/2025 U( 1 ) 357,048 D 0 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) Common Stock 08/14/2025 U( 1 ) 3,763,362 D 0 I See Footnotes ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Non-Voting Common Stock ( 9 ) ( 9 ) 08/14/2025 U( 1 ) 834,707 ( 9 ) ( 9 ) Common Stock 834,707 $ 0 0 I See Footnotes ( 2 ) ( 3 ) ( 4 ) Non-Voting Common Stock ( 9 ) ( 9 ) 08/14/2025 U( 1 ) 9,886,217 ( 9 ) ( 9 ) Common Stock 9,886,217 $ 0 0 I See Footnotes ( 3 ) ( 4 ) ( 8 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other BAKER BROS. ADVISORS LP 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 Former 10% owner and director 667, L.P. 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 Former 10% owner and director Baker Brothers Life Sciences LP 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 Former 10% owner and director BAKER FELIX 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 Former 10% owner and director BAKER JULIAN 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 Former 10% owner and director Baker Bros. Advisors (GP) LLC 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 Former 10% owner and director Signatures By: Baker Bros. Advisors LP, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 08/18/2025 Signature of Reporting Person Date Baker Bros. Advisors LP, Mgmt. Co. and Inv. Adviser to 667, L.P., pursuant to authority granted by Baker Biotech Capital, L.P., GP to 667, L.P. Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 08/18/2025 Signature of Reporting Person Date /s/ Felix J. Baker 08/18/2025 Signature of Reporting Person Date /s/ Julian C. Baker 08/18/2025 Signature of Reporting Person Date By: Baker Bros. Advisors (GP) LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 08/18/2025 Signature of Reporting Person Date Baker Bros. Advisors LP, Mgmt. Co. and Inv. Adviser to BAKER BROTHERS LIFE SCIENCES, L.P., pursuant to authority granted by Baker Brothers Life Sciences Capital, L.P., GP to Baker Brothers Life Sciences, L.P., /s/ Name: Scott L. Lessing, Title: President 08/18/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Reflects the completion of a tender offer by Concentra Biosciences, LLC (the "Parent"), to purchase all of the issued and outstanding shares of voting and non-voting common stock ("Shares") of the IGM Biosciences, Inc. (the "Issuer") for (i) $1.247 per Share in cash plus (ii) one non-transferable contractual contingent value right for each Share in connection with the consummation of the transactions (the "Merger") contemplated by the Agreement and Plan of Merger, dated as of July 1, 2025, by and among the Issuer, the Parent and Concentra Merger Sub V, Inc. ("Merger Sub"), a wholly owned subsidiary of Parent, pursuant to which, at the effective time of the Merger on August 14, 2025, Merger Sub merged with and into the Issuer, with the Issuer surviving as a subsidiary of Parent. ( 2 )As a result of their ownership interest in (i) Baker Biotech Capital, L.P. and (ii) 667, L.P. ("667"), Julian C. Baker and Felix J. Baker each may have been deemed to have had an indirect pecuniary interest in common stock of the Issuer ("Common Stock") reported as disposed in Table I and securities reported as disposed in Table II that were held directly by or that were held for the benefit of 667, a limited partnership of which the sole general partner is Baker Biotech Capital, L.P., a limited partnership of which the sole general partner is Baker Biotech Capital (GP), LLC, due to their interest in 667 and Baker Biotech Capital, L.P.'s right to receive an allocation of a portion of the profits from 667. ( 3 )Baker Bros. Advisors LP (the "Adviser") serves as the investment adviser to 667 and Baker Brothers Life Sciences, L.P. ("Life Sciences", and togeher with 667, the "Funds"). In connection with the services provided by the Adviser, the Adviser receives an asset-based management fee that does not confer any pecuniary interest in the securities held directly by the Funds or for the benefit of the Funds. The Adviser GP is the Adviser's sole general partner. Julian C. Baker and Felix J. Baker are managing members of the Adviser GP. The Adviser has complete and unlimited discretion and authority with respect to the investment and voting power of the securities held directly by the Funds or for the benefit of the Funds. The general partners of the Funds relinquished to the Adviser all discretion and authority with respect to the investment and voting power of the securities held directly by the Funds or for the benefit of the Funds. ( 4 )Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by the Funds or for the benefit of the Funds except to the extent of their pecuniary interest therein, and this report shall not be deemed an admission that any of Julian C. Baker, Felix J. Baker, the Adviser GP or the Adviser is or was a beneficial owner of such securities for purposes of Section 16 or any other purpose. ( 5 )Includes the disposal of 12,098 shares of Common Stock previously issued to Felix J. Baker pursuant to the Issuer's Outside Director Compensation Policy (the "Stock Incentive Plan") in lieu of director retainer fees in his previous capacity as a director of the Issuer and 892 shares of Common Stock previously issued to Dr. Kelvin Neu, a former employee of the Adviser, pursuant to the Stock Incentive Plan in lieu of director retainer fees, and 11,210 shares of Common Stock received previously from the exercise of 11,210 non-qualified options exercisable solely into Common Stock ("Stock Options") that were issued to Dr. Neu in his previous capacity as a director of the Issuer, of which the Funds were deemed to own a portion. ( 6 )Pursuant to the policies of the Adviser, Felix J. Baker does not have any right to any of the Issuer's securities issued as compensation for his previous service on the board of directors of the Issuer (the "Board") and Dr. Neu, a former employee of the Adviser, does not have any right to any of the Issu er's securities issued as compensation for his previous service on the Board and the Funds were entitled to an indirect proportionate pecuniary interest in the Stock Options and restricted stock units (each an "RSU"). Solely as a result of their ownership interest in (i) the general partners of the Funds and (ii) the Funds, Felix J. Baker and Julian C. Baker may have been deemed to have had an indirect pecuniary interest in the Stock Options, RSUs and any Common Stock acquired upon the exercise of Stock Options or vesting of RSUs (i.e. no direct pecuniary interest). ( 7 )Pursuant to the policies of the Adviser, the Adviser has voting and dispositive power over the Common Stock received in lieu of director retainer fees, Stock Options, RSUs and any Common Stock received as a result of the exercise of Stock Options. ( 8 )As a result of their ownership interest in (i) Baker Brothers Life Sciences Capital, L.P. and (ii) Life Sciences, Julian C. Baker and Felix J. Baker each may have been deemed to have had an indirect pecuniary interest in Common Stock reported as disposed in Table I and securities reported as disposed in Table II that were held directly by or that were held for the benefit of Life Sciences, a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital, L.P., a limited partnership of which the sole general partner is Baker Brothers Life Sciences Capital (GP), LLC, due to their interest in Life Sciences and Baker Brothers Life Sciences Capital, L.P.'s right to receive an allocation of a portion of the profits from Life Sciences. ( 9 )Represents non-voting common stock of the Issuer ("Non-Voting Common Stock") with no expiration date that was convetible at any time at the option of the holder on a 1-for-1 basis without consideration into Common Stock to the extent that after giving effect to such conversion, the holders thereof, together with their affiliates and any members of a Section 13(d) group with such holders, would have beneficially owned, for purposes of Rule 13d-3 under the Securities Act of 1934, as amended, no more than 4.99% of the outstanding shares of Common Stock (the "Beneficial Ownership Limitation") following such conversion. By written notice to the Issuer, the Funds may have from time to time been able to increase or decrease the Beneficial Ownership Limitation applicable to that Fund to any other percentage not in excess of 19.99%. Any such change would not have been effective until the 61st day after such notice is delivered to the Issuer.

Remarks: Felix J. Baker, a managing member of Baker Bros. Advisors (GP) LLC, the sole general partner of Baker Bros. Advisors LP, resigned as a director of IGM Biosciences, Inc. (the "Issuer") immediatley prior to the closing of the merger with Concentra Biosciences, LLC. For purposes of Section 16 of the Securities Exchange Act of 1934, as amended, the reporting persons other than Felix J. Baker are no longer deemed directors by deputization of the Issuer.

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