Sec Form 4 Filing - BAKER BROS. ADVISORS LP @ Kiniksa Pharmaceuticals, Ltd. - 2023-06-06

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 Kiniksa Pharmaceuticals, Ltd. [ KNSA] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 860 WASHINGTON STREET, 3RD FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 06/06/2023 (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 Class A Common Shares 14,840 ( 1 ) D Class A Common Shares 14,840 ( 2 ) D Class A Common Shares 06/06/2023 A 8,746 ( 3 ) A $ 0 117,726 I See Footnotes ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) Class A Common Shares 06/06/2023 A 8,746 ( 3 ) A $ 0 2,719,343 I See Footnotes ( 3 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) ( 10 )

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-Qualified Share Option (right to buy) $ 15.19 06/06/2023 A 52,472 ( 11 ) ( 11 ) 06/05/2033 Class A Common Shares 52,472 $ 0 52,472 I See Footnotes ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) ( 11 ) Non-Qualified Share Option (right to buy) $ 15.19 06/06/2023 A 52,472 ( 11 ) ( 11 ) 06/05/2033 Class A Common Shares 52,472 $ 0 52,472 I See Footnotes ( 5 ) ( 6 ) ( 7 ) ( 8 ) ( 9 ) ( 10 ) ( 11 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other BAKER BROS. ADVISORS LP 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X 667, L.P. 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X BAKER JULIAN 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X BAKER FELIX 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X Baker Bros. Advisors (GP) LLC 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X Baker Brothers Life Sciences LP 860 WASHINGTON STREET, 3RD FLOOR NEW YORK, NY10014 X Signatures By: Baker Bros. Advisors LP,Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 06/08/2023 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 06/08/2023 Signature of Reporting Person Date /s/ Julian C. Baker 06/08/2023 Signature of Reporting Person Date /s/ Felix J. Baker 06/08/2023 Signature of Reporting Person Date By: Baker Bros. Advisors (GP) LLC, Name: Scott L. Lessing, Title: President /s/ Scott L. Lessing 06/08/2023 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., Name: Scott L. Lessing, Title: President /s/ 06/08/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Class A common shares ("Class A Common Shares") of Kiniksa Pharmaceuticals, Ltd. (the "Issuer") held directly by Felix J. Baker. ( 2 )Class A Common Shares held directly by Julian C. Baker. ( 3 )Includes 4,373 restricted stock units (each an "RSU") payable solely in Class A Common Shares granted by the Issuer to each of Felix J. Baker, a managing member of Baker Bros. Advisors (GP) LLC (the "Adviser GP") and Dr. Stephen R. Biggar, an employee of Baker Bros. Advisors LP (the "Adviser") on June 6, 2023, pursuant to the Issuer's 2018 Incentive Award Plan (the "Incentive Award Plan"). The RSUs fully vest on the first anniversary of the grant date subject to the applicable director's continuous service on the board of directors of the Issuer (the "Board") through the vesting date. Felix J. Baker and Dr. Biggar serve on the Board as representatives of 667, L.P. ("667") and Baker Brothers Life Sciences, L.P. ("Life Sciences", and together with 667, the "Funds"). ( 4 )After giving effect to the transactions reported herein and as a result of their ownership interest in (i) Baker Biotech Capital, L.P. and (ii) 667, Julian C. Baker and Felix J. Baker each may be deemed to have an indirect pecuniary interest in Class A Common Shares reported in column 5 of Table I and the Share Options (as defined below) reported in column 9 of Table II held directly by or 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. ( 5 )Pursuant to the policies of the Adviser, Felix J. Baker and Dr. Biggar do not have a right to any of the Issuer's securiti es issued as compensation for their service on the Board and the Funds are entitled to an indirect proportionate pecuniary interest in the securities. The Funds each own an indirect proportionate pecuniary interest in the non-qualified options exercisable solely into Class A Common Shares ("Share Options") and RSUs. 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 be deemed to have an indirect pecuniary interest in the Share Options, RSUs and any Class A Common Shares acquired upon the exercise of Share Options or vesting of RSUs (i.e. no direct pecuniary interest). ( 6 )The Adviser serves as the investment adviser to the Funds. In connection with the services provided by the Adviser, the Adviser receives an asset-basedmanagement fee that does not confer any pecuniary interest in the securities held by 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 by 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 by the Funds. ( 7 )Julian C. Baker, Felix J. Baker, the Adviser GP and the Adviser disclaim beneficial ownership of the securities held directly by or held 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 a beneficial owner of such securities for purposes of Section 16 or any other purpose. ( 8 )Pursuant to agreements between Felix J. Baker, Dr. Biggar and the Adviser and the policies of the Adviser, the Adviser has voting and dispositive power over the Share Options, RSUs and any Class A Common Shares received as a result of the exercise of Share Options or vesting of RSUs. ( 9 )The acquisitions of the RSUs and Share Options reported on this form represent grants to each of Felix J. Baker and Dr. Biggar of 4,373 RSUs on Table I and 26,236 Share Options on Table II. These grants, totaling 8,746 RSUs and 52,472 Share Options for Felix J. Baker and Dr. Biggar in the aggregate, are reported for each of the Funds as each has an indirect pecuniary interest in such securities. ( 10 )After giving effect to the transactions reported herein and 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 be deemed to have an indirect pecuniary interest in Class A Common Shares reportedin column 5 of Table I and the Share Options reported in column 9 of Table II held directly by or 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 inLife Sciences and Baker Brothers Life Sciences Capital, L.P.'s right to receive an allocation of a portion of the profits from Life Sciences. ( 11 )Includes 26,236 Share Options granted by the Issuer to each of Felix J. Baker and Dr. Biggar on June 6, 2023, pursuant to the Incentive Award Plan. The Share Options have a strike price of $15.19, vest in 12 equal monthly installments and expire 10 years from the date of grant.

Remarks: Felix J. Baker, a managing member of Baker Bros. Advisors (GP) LLC and Dr. Stephen R. Biggar, a full-time employee of Baker Bros. Advisors LP are directors of Kiniksa Pharmaceuticals, Ltd. (the "Issuer"). By virtue of their representation on the board of directors of the Issuer, for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, the reporting persons other than Felix J. Baker are deemed directors by deputization of the Issuer.

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