Sec Form 4 Filing - Clarus Lifesciences III, L.P. @ Annexon, Inc. - 2020-07-28

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 Clarus Lifesciences III, L.P. 2. Issuer Name and Ticker or Trading Symbol Annexon, Inc. [ ANNX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 101 MAIN STREET, SUITE 1210, 3. Date of Earliest Transaction (MM/DD/YY) 07/28/2020 (Street) CAMBRIDGE, MA02142 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 07/28/2020 C 643,208 A 643,208 I See Footnotes ( 5 ) ( 6 ) ( 7 ) Common Stock 07/28/2020 C 950,134 A 1,593,342 I See Footnotes ( 5 ) ( 6 ) ( 7 ) Common Stock 07/28/2020 C 697,860 A 2,291,202 I See Footnotes ( 5 ) ( 6 ) ( 7 ) Common Stock 07/28/2020 C 239,433 A 2,530,635 I See Footnotes ( 5 ) ( 6 ) ( 7 ) Common Stock 07/28/2020 P 200,000 A $ 17 2,730,635 I See Footnotes ( 5 ) ( 6 ) ( 7 )

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 Series A-1 Redeemable Convertible Preferred Stock ( 1 ) 07/28/2020 C 5,666,667 ( 1 ) ( 1 ) Common Stock 643,208 ( 1 ) ( 1 ) 0 I See Footnotes ( 5 ) ( 6 ) ( 7 ) Series B Redeemable Convertible Preferred Stock ( 2 ) 07/28/2020 C 8,370,685 ( 2 ) ( 2 ) Common Stock 950,134 ( 2 ) ( 2 ) 0 I See Footnotes ( 5 ) ( 6 ) ( 7 ) Series C Redeemable Convertible Preferred Stock ( 3 ) 07/28/2020 C 6,148,147 ( 3 ) ( 3 ) Common Stock 697,860 ( 3 ) ( 3 ) 0 I See Footnotes ( 5 ) ( 6 ) ( 7 ) Series D Redeemable Convertible Preferred Stock ( 4 ) 07/28/2020 C 2,109,407 ( 4 ) ( 4 ) Common Stock 239,433 ( 4 ) ( 4 ) 0 I See Footnotes ( 5 ) ( 6 ) ( 7 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Clarus Lifesciences III, L.P. 101 MAIN STREET, SUITE 1210 CAMBRIDGE, MA02142 X Clarus Ventures III GP, L.P. 101 MAIN STREET, SUITE 1210 CAMBRIDGE, MA02142 X Blackstone Clarus III L.L.C. C/O THE BLACKSTONE GROUP INC. 345 PARK AVENUE NEW YORK, NY10154 X Blackstone Holdings II L.P. C/O THE BLACKSTONE GROUP INC. 345 PARK AVENUE NEW YORK, NY10154 X Blackstone Holdings I/II GP L.L.C. C/O THE BLACKSTONE GROUP INC. 345 PARK AVENUE NEW YORK, NY10154 X Blackstone Group Inc 345 PARK AVENUE NEW YORK, NY10154 X Blackstone Group Management L.L.C. C/O THE BLACKSTONE GROUP INC. 345 PARK AVENUE NEW YORK, NY10154 X SCHWARZMAN STEPHEN A C/O THE BLACKSTONE GROUP INC. 345 PARK AVENUE NEW YORK, NY10154 X Signatures CLARUS LIFESCIENCES III, L.P., By: Clarus Ventures III GP, L.P., its GP, By: Blackstone Clarus III L.L.C., its GP, By: Blackstone Holdings II L.P., its managing member, By: Blackstone Holdings I/II GP L.L.C., its GP, By /s/ John G. Finley, Title: CLO 07/30/2020 Signature of Reporting Person Date CLARUS VENTURES III GP, L.P., By: Blackstone Clarus III L.L.C., its GP, By: Blackstone Holdings II L.P., its managing member, By: Blackstone Holdings I/II GP L.L.C., its GP, By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 07/30/2020 Signature of Reporting Person Date BLACKSTONE CLARUS III L.L.C., By: Blackstone Holdings II L.P., its managing member, By: Blackstone Holdings I/II GP L.L.C., its general partner, By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 07/30/2020 Signature of Reporting Person Date BLA CKSTONE HOLDINGS II L.P., By: Blackstone Holdings I/II GP L.L.C., its general partner, By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 07/30/2020 Signature of Reporting Person Date BLACKSTONE HOLDINGS I/II GP L.L.C., By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 07/30/2020 Signature of Reporting Person Date THE BLACKSTONE GROUP INC., By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 07/30/2020 Signature of Reporting Person Date BLACKSTONE GROUP MANAGEMENT L.L.C., By: /s/ John G. Finley, Name: John G. Finley, Title: Chief Legal Officer 07/30/2020 Signature of Reporting Person Date /s/ Stephen A. Schwarzman 07/30/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The shares of Series A-1 Redeemable Convertible Preferred Stock of the Issuer were automatically converted on a 1-for-8.81 basis into common stock of the Issuer ("Common Stock") immediately prior to the closing of the Issuer's initial public offering. ( 2 )The shares of Series B Redeemable Convertible Preferred Stock of the Issuer were automatically converted on a 1-for-8.81 basis into Common Stock immediately prior to the closing of the Issuer's initial public offering. ( 3 )The shares of Series C Redeemable Convertible Preferred Stock of the Issuer were automatically converted on a 1-for-8.81 basis into Common Stock immediately prior to the closing of the Issuer's initial public offering. ( 4 )The shares of Series D Redeemable Convertible Preferred Stock of the Issuer were automatically converted on a 1-for-8.81 basis into Common Stock immediately prior to the closing of the Issuer's initial public offering. ( 5 )Reflects securities held directly by Clarus Lifesciences III, L.P. Clarus Ventures III GP, L.P. is the general partner of Clarus Lifesciences III, L.P. Blackstone Clarus III L.L.C. is the general partner of Clarus Ventures III GP, L.P. The sole member of Blackstone Clarus III L.L.C. is Blackstone Holdings II L.P. The general partner of Blackstone Holdings II L.P. is Blackstone Holdings I/II GP L.L.C. The sole member of Blackstone Holdings I/II GP L.L.C. is The Blackstone Group Inc. The sole holder of the Class C common stock of The Blackstone Group Inc. is Blackstone Group Management L.L.C. Blackstone Group Management L.L.C. is wholly-owned by Blackstone's senior managing directors and controlled by its founder, Stephen A. Schwarzman. ( 6 )Information with respect to each of the Reporting Persons is given solely by such Reporting Person, and no Reporting Person has responsibility for the accuracy or completeness of information supplied by another Reporting Person. ( 7 )Each of the Reporting Persons (other than to the extent it directly holds securities reported herein) disclaims beneficial ownership of the securities held by the other Reporting Persons, except to the extent of such Reporting Person's pecuniary interest therein, and, pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934, each of the Reporting Persons (other than to the extent it directly holds securities reported herein) states that the inclusion of these securities in this report shall not be deemed an admission of beneficial ownership of all of the reported securities for purposes of Section 16 or for any other purpose.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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