Sec Form 3/A Filing - MARINER JONATHAN D @ OneStream, Inc. - 2024-07-24

FORM 3/A 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 MARINER JONATHAN D 2. Issuer Name and Ticker or Trading Symbol OneStream, Inc. [ OS] 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) C/O ONESTREAM, INC., 191 N. CHESTER STREET 3. Date of Earliest Transaction (MM/DD/YY) 07/24/2024 (Street) BIRMINGHAM, MI48009 4. If Amendment, Date Original Filed (MM/DD/YY) 07/24/2024 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ 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

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 Common Units $ 0 ( 1 ) ( 1 ) Class D Common Stock ( 2 ) 325,233 D Common Units $ 0 ( 1 ) ( 1 ) Class D Common Stock ( 2 ) 46,079 I See footnote ( 3 ) Common Units $ 0 ( 1 ) ( 1 ) Class D Common Stock ( 2 ) 46,079 I See footnote ( 4 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other MARINER JONATHAN D C/O ONESTREAM, INC. 191 N. CHESTER STREET BIRMINGHAM, MI48009 X Signatures /s/ Holly Koczot, attorney-in-fact 07/26/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The Common Units may be redeemed by the Reporting Person for shares of Class D Common Stock on a 1:1 basis, and a corresponding number of shares of Class C Common Stock will be forfeited in connection with the redemption. The Common Units have no expiration date. The Class D Common Stock is in turn convertible at any time, at the holder's election, into Class A Common Stock on a 1:1 basis. Each outstanding share of Class D Common Stock will automatically convert into one share of Class A Common Stock on the first trading day following the seventh anniversary of the Issuer's initial public offering. ( 2 )The Form 3/A corrects the title of the underlying derivative security. ( 3 )The Common Units held of record by the Jonathan D. Mariner Revocable Trust, or the Mariner Revocable Trust, of which the Reporting Person is a trustee. By virtue of his relationship, the Reporting Person may be deemed to hold voting and dispositive power with respect to the Common Units held by the Mariner Revocable Trust. ( 4 )The Common Units held of record by the Mariner Family Equity Trust, of which the Reporting Person is trustee. By virtue of his relationship, the Reporting Person may be deemed to hold voting and dispositive power with respect to the Common Units held by the Mariner Family Equity Trust.

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).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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