Sec Form 4 Filing - MARINER JONATHAN D @ OneStream, Inc. - 2025-03-24

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

OMB APPROVAL OMB Number: 3235-0287 Expires: November 30, 2011 Estimated average burden hours per response... 0.5

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) 03/24/2025 (Street) BIRMINGHAM, MI48009 4. If Amendment, Date Original Filed (MM/DD/YY) 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 Class A Common Stock 03/24/2025 C( 1 ) 46,411 A 46,411 D

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 ( 2 ) 03/24/2025 C( 2 ) 46,411 ( 3 ) ( 3 ) Class D Common Stock 46,411 < /td> $ 0 206,949 D Class D Common Stock ( 2 ) 03/24/2025 C( 2 ) 46,411 ( 4 ) ( 4 ) Class A Common Stock 46,411 $ 0 46,411 D Class D Common Stock ( 1 ) 03/24/2025 C( 1 ) 46,411 ( 4 ) ( 4 ) Class A Common Stock 46,411 $ 0 0 D Common Units $ 0 ( 3 ) ( 3 ) Class D Common Stock 40,051 40,051 I See footnote ( 5 )

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 03/26/2025 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The Class A Common Stock was acquired upon the conversion, at the holder's election, of Class D Common Stock held by the holder on a 1:1 basis. ( 2 )On March 24, 2025, the holder redeemed 46,411 Common Units of OneStream Software LLC, and 46,411 shares of the holder's Class C Common Stock were cancelled, in exchange for 46,411 shares of Class D Common Stock. ( 3 )The Common Units may be redeemed by the holder for shares of Class D Common Stock on a 1:1 basis, and an equal number of the holder's shares of Class C Common Stock (which have no economic rights) will be cancelled in connectionwith the redemption. The Common Units have no expiration date. ( 4 )The Class D Common Stock is 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 upon the earlier of (i) any transfer, whether or not for value, except for certain transfers exempted by the Issuer's amended and restated certificate of incorporation, (ii) death or incapacity (if the holder is a natural person), and (iii) the first trading day following the seventh anniversary of the Issuer's initial public offering. ( 5 )Held by the Jonathan D. Mariner Revocable Trust, of which the Reporting Person is a trustee.

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).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.