# EDGAR Filing Document

**Accession Number:** 0001889956
**File Stem:** 0001063663-26-000004
**Filing Date:** 2026-4
**Character Count:** 8618
**Document Hash:** 5a26656e1304c68bb2b32059e0601b3d
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001063663-26-000004.hdr.sgml**: 20260402

**ACCESSION NUMBER**: 0001063663-26-000004

**CONFORMED SUBMISSION TYPE**: 4

**PUBLIC DOCUMENT COUNT**: 1

**CONFORMED PERIOD OF REPORT**: 20260401

**FILED AS OF DATE**: 20260402

**DATE AS OF CHANGE**: 20260402

**REPORTING-OWNER**: 

**OWNER DATA:**
- **COMPANY CONFORMED NAME:** MARINER JONATHAN D
- **CENTRAL INDEX KEY:** 0001063663

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** 4
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-42187
- **FILM NUMBER:** 26835759

**MAIL ADDRESS:**
- **STREET 1:** 2200 WEST DON TYSON PARKWAY
- **CITY:** SPRINGDALE
- **STATE:** AR
- **ZIP:** 72762
**ISSUER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** OneStream, Inc.
- **CENTRAL INDEX KEY:** 0001889956
- **STANDARD INDUSTRIAL CLASSIFICATION:** SERVICES-PREPACKAGED SOFTWARE [7372]
- **ORGANIZATION NAME:** 06 Technology
- **EIN:** 873199478
- **FISCAL YEAR END:** 1231

**BUSINESS ADDRESS:**
- **STREET 1:** 191 N. CHESTER STREET
- **CITY:** BIRMINGHAM
- **STATE:** MI
- **ZIP:** 48009
- **BUSINESS PHONE:** (248) 650-1490

**MAIL ADDRESS:**
- **STREET 1:** 191 N. CHESTER STREET
- **CITY:** BIRMINGHAM
- **STATE:** MI
- **ZIP:** 48009

### UNITED STATES SECURITIES AND EXCHANGE COMMISSION
**Washington, D.C. 20549**

## FORM 4

### STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

[x] 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 for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

---

| | | |
|:---|:---|:---|
| **1. Name and Address of Reporting Person**<sup>*</sup><br>MARINER JONATHAN D<br><sub>(Last) (First) (Middle)</sub><br>C/O ONESTREAM, INC.<br>191 N. CHESTER STREET<br><sub>(Street)</sub><br>BIRMINGHAM, MI 48009<br><sub>(City) (State) (Zip)</sub> | **3. Date of Earliest Transaction (Month/Day/Year)**<br>2026-04-01 | **5. Relationship of Reporting Person(s) to Issuer**<br>(Check all applicable)<br>[X] Director [ ] 10% Owner<br>[ ] Officer (give title below) [ ] Other (specify below)<br>_ _ |
| **2. Issuer Name and Ticker or Trading Symbol**<br>OneStream, Inc. [ OS ] | **4. If Amendment, Date of Original Filed (Month/Day/Year)**<br>  | **6. Individual or Joint/Group Filing (Check Applicable Line)**<br>[X] Form filed by One Reporting Person<br>[ ] Form filed by More than One Reporting Person |

---

## Table I - Non-Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | 3. Transaction Code (V) | 3. Transaction Code (V) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 4. Securities Acquired (A) or Disposed of (D) | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| 1. Title of Security | 2. Transaction Date | 2A. Deemed Execution Date | Code | V | Amount | (A) or (D) | Price | 5. Amount of Securities Beneficially Owned | 6. Ownership Form | 7. Nature of Indirect Beneficial Ownership |
| Class A Common Stock | 2026-04-01 |  | D<sup>(1)</sup> |  | 7130 | D | <sup>(2)</sup> | 0 | D |  |

---

## Table II - Derivative Securities

---

|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | 4. Transaction Code (V) | 4. Transaction Code (V) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 5. Number of Derivative Securities Acquired (A) or Disposed of (D) | 6. Date Exercisable and Expiration Date | 6. Date Exercisable and Expiration Date | 7. Title and Amount of Underlying Securities | 7. Title and Amount of Underlying Securities | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| 1. Title of Derivative Security | 2. Conversion or Exercise Price | 3. Transaction Date | 3A. Deemed Execution Date | Code | V | (A) | (D) | Date Exercisable | Expiration Date | Title | Amount or Number of Shares | 8. Price of Derivative Security | 9. Number of Derivative Securities Beneficially Owned | 10. Ownership Form | 11. Nature of Indirect Beneficial Ownership |
| Common Units | <sup>(3)</sup> | 2026-04-01 |  | D<sup>(1)</sup> |  |  | 206949 | <sup>(3)</sup> | <sup>(3)</sup> | Class D Common Stock | 206949 | <sup>(3)</sup> | 0 | D |  |
| Common Units | <sup>(3)</sup> | 2026-04-01 |  | D<sup>(1)</sup> |  |  | 40051 | <sup>(3)</sup> | <sup>(3)</sup> | Class D Common Stock | 40051 | <sup>(3)</sup> | 0 | I | See Footnote<sup>(4)</sup> |
| Stock Option (right to buy) | $16.40 | 2026-04-01 |  | D<sup>(1)</sup> |  |  | 50000 | <sup>(5)</sup> | 2034-06-20 | Class A Common Stock | 50000 | <sup>(5)</sup> | 0 | D |  |
| Stock Option (right to buy) | $20 | 2026-04-01 |  | D<sup>(1)</sup> |  |  | 134913 | <sup>(5)</sup> | 2034-07-22 | Class A Common Stock | 134913 | <sup>(5)</sup> | 0 | D |  |

---

### Footnotes:

(1) Pursuant to the Agreement and Plan of Merger (the "Merger Agreement"), dated January 6, 2026, by and among OneStream, Inc. ("Issuer"), OneStream Software LLC, a subsidiary of Issuer ("Company LLC"), Onward AcquireCo Inc. ("Parent"), Onward Merger Sub 2, LLC ( "Merger Sub I") and Onward Merger Sub, Inc. ("Merger Sub II"), on April 1, 2026, Merger Sub 1 merged with and into Company LLC (the "First Merger"), with Company LLC surviving the First Merger and becoming a subsidiary of Parent, and Merger Sub II merged with and into Issuer (the "Second Merger" and together with the First Merger, the "Mergers"), with Issuer surviving the Second Merger and becoming a subsidiary of Parent.

(2) Represents an equal number of restricted stock units ("RSUs"). Pursuant to Issuer's outside director compensation policy, immediately before the effective time of the Mergers (the "Effective Time"), each RSU award held by a non-employee director that was outstanding and unvested as of immediately before the Effective Time (a "Director RSU Award") accelerated and became fully vested. At the Effective Time, each Director RSU Award was cancelled and converted into the right to receive an amount in cash, without interest, equal to the product of (a) $24.00 (the "Per Share Price") multiplied by (b) the total number of shares of Issuer's Class A Common Stock covered by such Director RSU Award, less applicable withholding taxes.

(3) At the Effective Time, each Common Unit was cancelled and converted into the right to receive an amount in cash, without interest, equal to the Per Share Price, less applicable withholding taxes.  Each corresponding share of Class C Common Stock was cancelled and converted into the right to receive $0.0001 in cash, without interest, less applicable withholding taxes.

(4) Held by the Jonathan D. Mariner Revocable Trust, of which the Reporting Person is a trustee.

(5) Pursuant to Issuer's outside director compensation policy, immediately prior to the Effective Time, the shares subject to the option became fully vested and immediately exercisable.  At the Effective Time, the option was cancelled and converted into the right to receive an amount in cash, without interest, equal to the product of  (a) the total number of shares of Class A Common Stock subject to the option multiplied by (b) the excess, if any, of the Per Share Price over the exercise price per share of such option, less applicable withholding taxes.

**Signature:** /s/ Holly Koczot, attorney-in-fact  
**Date:** 2026-04-02

### Remarks:

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.**