Sec Form 4 Filing - BAIN CAPITAL INVESTORS LLC @ Waystar Holding Corp. - 2024-12-12

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 BAIN CAPITAL INVESTORS LLC 2. Issuer Name and Ticker or Trading Symbol Waystar Holding Corp. [ WAY] 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) 200 CLARENDON STREET 3. Date of Earliest Transaction (MM/DD/YY) 12/12/2024 (Street) BOSTON, MA02116 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 Ordinary Shares, $0.01 par value 12/12/2024 J( 2 ) 23,936,936 D 4,043,481 I See Footnote ( 1 ) Ordinary Shares, $0.01 par value 12/12/2024 J( 2 ) 23,936,936 A 27,980,417 I See Footnote ( 1 )

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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other BAIN CAPITAL INVESTORS LLC 200 CLARENDON STREET BOSTON, MA02116 X BCPE Derby Investor, LP 200 CLARENDON STREET BOSTON, MA02116 X BCPE Derby GP, LLC 200 CLARENDON STREET BOSTON, MA02116 X Bain Capital Fund XI, L.P. 200 CLARENDON STREET BOSTON, MA02116 X Bain Capital Partners XI, L.P. 200 CLARENDON STREET BOSTON, MA02116 X Signatures Bain Capital Investors, LLC, By: /s/ David Humphrey, Title: Authorized Signatory 12/16/2024 Signature of Reporting Person Date BCPE Derby Investor, LP, By: BCPE Derby GP, LLC, its general partner, By: Bain Capital Fund XI, L.P. its member, By: Bain Capital Partners XI, L.P. its general partner, By: Bain Capital Investors, LLC its manager, By: /s/ David Humphrey, Title: Authorized 12/16/2024 Signature of Reporting Person Date BCPE Derby GP, LLC, By: Bain Capital Fund XI, L.P. its member, By: Bain Capital Partners XI, L.P. its general partner, By: Bain Capital Investors, LLC its general partner, By: /s/ David Humphrey, Title: Authorized Signatory 12/16/2024 Signature of Reporting Person Date Bain Capital Fund XI, LP, By: Bain Capital Partners XI, LP, its general partner, By: Bain Capital Investors, LLC, its manager, By: /s/ David Humphrey, Title: Authorized Signatory 12/16/2024 Signature of Reporting Person Date Bain Capital Partners XI, LP, By: Bain Capital Investors, LLC, its manager, By: /s/ David Humphrey, Title: Authorized Signatory 12/16/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Bain Capital Fund XI, LP ("Fund XI") is the (i) sole member of BCPE Derby GP, LLC ("Derby GP"), which is the general partner of BCPE Derby Investor, LP ("Derby Investor"), and (ii) sole member of BCPE Derby (DE) SPV, LLC, ("Derby SPV GP"), which is the general partner of BCPE Derby (DE) SPV, LP ("Derby SPV Investor"). Bain Capital Investors, LLC ("BCI") is the manager of Bain Capital Partners XI, LP ("Partners XI" and, together with BCI, Derby GP, Derby Investor, Derby SPV GP, Derby SPV Investor and Fund XI, the "Bain Capital Entities"), which is the general partner of Fund XI. As a result, each of the Bain Capital Entities may be deemed to share voting and dispositive power with respect to the shares of Common Stock held by Derby Investor and Derby SPV Investor. Each of the Bain Capital Entities disclaims beneficial ownership of such securities, except to the extent of its pecuniary interest therein. ( 2 )On December 12, 2024, Derby SPV Investor received 23,936,936 shares of Common Stock (the "Shares") in a transaction that is exempt from Section 16 pursuant to Rule 16a-13, wherein Derby Investor distributed the Shares to Fund XI, and then Fund XI immediately contributed the Shares to Derby SPV Investor. Following the transaction, Derby Investor directly owns 4,043,481 shares and Derby SPV Investor directly owns 23,936,936 shares.

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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