Sec Form 3 Filing - Shea Thomas Anthony @ OneStream, Inc. - 2024-07-24

FORM 3 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 Shea Thomas Anthony 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 X __ Officer (give title below) _____ Other (specify below) Chief Executive Officer (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) 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 Stock Option (right to buy) $ 10.65 ( 1 ) 12/04/2031 Class A Common Stock 619,835 D Stock Option (right to buy) $ 10.65 ( 2 ) 03/05/2033 Class A Common Stock 654,451 D Stock Option (right to buy) $ 14.51 ( 3 ) 03/10/2034 Class A Common Stock 908,169 D Class D Common Stock $ 0 ( 4 ) ( 4 ) Class A Common Stock 3,553,463 D Class D Common Stock $ 0 ( 4 ) ( 4 ) Class A Common Stock 7,525,803 I See footnote ( 5 ) Class D Common Stock $ 0 ( 4 ) ( 4 ) Class A Common Stock 5,090,738 I See footnote ( 6 ) Common Units $ 0 ( 7 ) ( 7 ) Class D Common Stock 325,232 I See footnote ( 8 ) Stock Option (right to buy) $ 20 ( 9 ) 07/22/2034 Class A Common Stock 148,787 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Shea Thomas Anthony C/O ONESTREAM, INC. 191 N. CHESTER STREET BIRMINGHAM, MI48009 X Chief Executive Officer Signatures /s/ Holly Koczot, attorney-in-fact 07/24/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )One-fourth of the shares subject to the option vested on February 15, 2023, and 1/48th of the shares subject to the option vest each month thereafter, subject to the Reporting Person continuing to be a service provider through the applicable vesting date. ( 2 )One-fourth of the shares subject to the option vested on February 15, 2024, and 1/48th of the shares subject to the option shall vest each month thereafter, subject to the Reporting Person continuing to be a service provider through the applicable vesting date. ( 3 )One-fourth of the shares subject to the option shall vest on February 15, 2025, and 1/48th of the shares subject to the option shall vest each month thereafter, subject to the Reporting Person continuing to be a service provider through the applicable vesting 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 our Class A Common Stock on the first trading day following the seventh anniversary of the Issuer's initial public offering. ( 5 )Shares held of record by the Shea Family Trust dated December 25, 2019, or the 2019 Shea Family Trust. The Reporting Person's spouse serves as the co-trustee for the 2019 Shea Family Trust. By virtue of his relationship, the Reporting Person may be deemed to share voting and dispositive power with respect to the shares held by the 2019 Shea Family Trust. ( 6 )Shares held of record by the Thomas A. Shea 2020 Annuity Trust dated December 23, 2020, or the 2020 Shea Annuity Trust. The Reporting Person's spouse serves as the trustee for the 2020 Shea Annuity Trust. By virtue of his relationship, the Reporting Person may be deemed to share voting and dispositive power with respect to the shares held by the 2020 Shea Annuity Trust. ( 7 )The Common Units may be redeemed by the Reporting Person at any time on or following the closing of the Issuer's initial public offering 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. ( 8 )Shares held of record by the TSICU Corp. TSICU Corp. is a subchapter S corporation controlled by the Reporting Person, who has sole voting and dispositive power over the shares held by it. ( 9 )One-sixteenth of the shares subject to the option shall vest October 23, 2024, and one-sixteenth of the shares subject to the option shall vest every three months thereafter, subject to the Reporting Person continuing to be a service provider through the applicable vesting date.

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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