Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b). Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 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 (Month/Day/Year) 09/12/2025 (Street) BOSTON, MA 02116 4. If Amendment, Date Original Filed (Month/Day/Year) 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 (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 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, par value $0.01 per share 09/12/2025 S(3) 4,295,139 D $39.21(3) 13,759,910 I See Footnote(1)(2) Common Stock, par value $0.01 per share 09/12/2025 J(4) 516,371 D (4) 13,243,539 I See Footnote(1)(2)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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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 (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

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 (Month/Day/Year)

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, MA 02116		X
BCPE Derby Investor, LP 200 CLARENDON STREET BOSTON, MA 02116		X
BCPE Derby GP, LLC 200 CLARENDON STREET BOSTON, MA 02116		X
Bain Capital Fund XI, L.P. 200 CLARENDON STREET BOSTON, MA 02116		X
Bain Capital Partners XI, L.P. 200 CLARENDON STREET BOSTON, MA 02116		X
BCPE Derby (DE) SPV, LP C/O BAIN CAPITAL PRIVATE EQUITY, LP 200 CLARENDON STREET BOSTON, MA 02116		X
BCPE Derby (DE) SPV (GP), LLC 200 CLARENDON STREET BOSTON, MA 02116		X

Signatures

Bain Capital Investors, LLC, By: /s/ Paul Moskowitz, Title: Authorized Signatory		09/16/2025
**Signature of Reporting Person		Date
BCPE Derby Investor, LP, By: BCPE Derby GP, LLC, its GP, By: Bain Capital Fund XI, L.P., its member, By: Bain Capital Partners XI, L.P., its GP, By: Bain Capital Investors, LLC, its GP, By: /s/ Paul Moskowitz, Title: Authorized Signatory		09/16/2025
**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/ Paul Moskowitz, Title: Authorized Signatory		09/16/2025
**Signature of Reporting Person		Date
Bain Capital Fund XI, L.P., By: Bain Capital Partners XI, L.P., its general partner, By: Bain Capital Investors, LLC, its general partner, By: /s/ Paul Moskowitz, Title: Authorized Signatory		09/16/2025
**Signature of Reporting Person		Date
Bain Capital Partners XI, L.P., By: Bain Capital Investors, LLC, its general partner, By: /s/ Paul Moskowitz, Title: Authorized Signatory		09/16/2025
**Signature of Reporting Person		Date
BCPE Derby (DE) SPV, LP, By: BCPE Derby (DE) SPV (GP), LLC, its GP, By: Bain Capital Fund XI, L.P., its member, By: Bain Capital Partners XI, L.P., its GP, By: Bain Capital Investors, LLC, its GP, By: /s/ Paul Moskowitz, Title: Authorized Signatory		09/16/2025
**Signature of Reporting Person		Date
BCPE Derby (DE) SPV (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/ Paul Moskowitz, Title: Authorized Signatory		09/16/2025
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Bain Capital Investors, LLC ("BCI") is the manager of Bain Capital Partners XI, L.P. ("Partners XI"), which is the general partner of Bain Capital Fund XI, L.P. ("Fund XI"). 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" and, together with BCI, Partners XI, Fund XI, Derby GP, Derby Investor and Derby SPV GP, the "Bain Capital Entities").
(2)	(Continued from footnote 1) As a result, the Bain Capital Entities may be deemed to share voting and dispositive power with respect to the shares of the Issuer's common stock, par value $0.01 per share (the "Common Stock"), held by Derby Investor and Derby SPV Investor. The Bain Capital Entities disclaim beneficial ownership of such securities except to the extent of their pecuniary interest therein.
(3)	Pursuant to a registered public offering that closed on September 12, 2025, 298,303 shares of Common Stock were sold by Derby Investor and 3,996,836 shares of Common Stock were sold by Derby SPV Investor at a price of $39.21 (net of underwriting discount).
(4)	On September 12, 2025, Derby Investor distributed 397,013 shares of Common Stock and Derby SPV Investor distributed 119,358 shares of Common Stock to one or more of their respective members or partners in connection with certain charitable gifts made by such members or partners or their direct or indirect owners. Such shares of Common Stock are subject to lock-up agreements that, subject to certain exceptions, restrict the sale of such shares until November 11, 2025 except with the prior written consent of J.P. Morgan Securities LLC.

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