Form of Underwriting Agreement

[ • ] Shares

ONESTREAM, INC.

CLASS A COMMON STOCK (PAR VALUE $0.0001 PER SHARE)

UNDERWRITING AGREEMENT

[ • ], 2024

[ • ], 2024

Morgan Stanley & Co. LLC

J.P. Morgan Securities LLC

as Representatives of the several

Underwriters listed in Schedule I hereto

c/o Morgan Stanley & Co. LLC

1585 Broadway

New York, New York 10036

c/o J.P. Morgan Securities LLC

383 Madison Avenue

New York, New York 10179

Ladies and Gentlemen:

OneStream, Inc., a Delaware corporation (the “Company”), proposes to issue and sell to the several Underwriters named in Schedule I hereto (the “Underwriters”), for whom Morgan Stanley & Co. LLC (“Morgan Stanley”) and J.P. Morgan Securities LLC (together, the “Representatives”) are acting as Representatives, and certain stockholders of the Company named in Schedule II hereto (the “Selling Stockholders”) severally propose to sell to the several Underwriters, an aggregate of [ • ] shares of the Class A common stock, $0.0001 par value per share, of the Company (the “Class A Common Stock”), of which [ • ] shares are to be issued and sold by the Company and [ • ] shares are to be sold by the Selling Stockholders, each Selling Stockholder selling the amount of shares set forth opposite such Selling Stockholder’s name in Schedule II hereto. Such shares of Class A Common Stock to be sold by the Company and the Selling Stockholders shall hereinafter be referred to as the “Firm Shares.”

The Company and the Selling Stockholders also propose to sell to the several Underwriters, severally and not jointly, not more than an additional [ • ] shares of Class A Common Stock (the “Additional Shares”), of which not more than [ • ] shares are to be issued and sold by the Company and not more than [ • ] shares are to be sold by the Selling Stockholders, each Selling Stockholder selling the amount of shares set forth opposite such Selling Stockholder’s name in Schedule II hereto, if and to the extent that you, as the Representatives, shall have determined to exercise, on behalf of the Underwriters, the right to purchase such shares of Class A Common Stock granted to the Underwriters in Section 3 hereof. The Firm Shares and the Additional Shares are hereinafter collectively referred to as the “Shares.” The shares of Class A Common Stock, together with the shares of Class B common stock, $0.0001 par value per share, of the Company, the shares of Class C common stock, $0.0001 par value per share, of the Company (the “Class C Common Stock”) and the shares of Class D common stock, $0.0001 par value per share, of the Company (the “Class D Common Stock”), are hereinafter referred to as the “Common Stock.” The Company and the Selling Stockholders are hereinafter sometimes collectively referred to as the “Sellers.”

The Company and OneStream Software LLC, a Delaware limited liability company (“OneStream LLC”), are collectively referred to herein as the “OneStream Parties.”

All references to “Subsidiaries” of the Company shall be understood to refer to its “significant subsidiaries” (as defined in Rule 1-02 of Regulation S-X under the Securities and Exchange Act of 1934, as amended (the “Exchange Act”)), including OneStream LLC.

The Company has filed with the Securities and Exchange Commission (the “Commission”) a registration statement on Form S-1 (File No. 333-[ • ]), including a preliminary prospectus, relating to the Shares. The registration statement as amended at the time it becomes effective, including the information (if any) deemed to be part of the registration statement at the time of effectiveness pursuant to Rule 430A under the Securities Act of 1933, as amended (the “Securities Act”), is hereinafter referred to as the “Registration Statement”; the prospectus in the form first used to confirm sales of Shares (or in the form first made available to the Underwriters by the Company to meet requests of purchasers pursuant to Rule 173 under the Securities Act) is hereinafter referred to as the “Prospectus.” If the Company has filed an abbreviated registration statement to register the sale of additional shares of Class A Common Stock pursuant to Rule 462(b) under the Securities Act (a “Rule 462 Registration Statement”), then any reference herein to the term “Registration Statement” shall be deemed to include such Rule 462 Registration Statement.

For purposes of this agreement (this “Agreement”), “free writing prospectus” has the meaning set forth in Rule 405 under the Securities Act, “preliminary prospectus” shall mean each prospectus used prior to the effectiveness of the Registration Statement, and each prospectus that omitted information pursuant to Rule 430A under the Securities Act that was used after such effectiveness and prior to the execution and delivery of this Agreement, “Time of Sale Prospectus” means the preliminary prospectus contained in the Registration Statement at the time of its effectiveness together with the documents and pricing information set forth in Schedule III hereto, and “broadly available road show” means a “bona fide electronic road show” as defined in Rule 433(h)(5) under the Securities Act that has been made available without restriction to any person. As used herein, the terms “Registration Statement,” “preliminary prospectus,” “Time of Sale Prospectus” and “Prospectus” shall include the documents, if any, incorporated by reference therein as of the date hereof.

1. Representations and Warranties of the OneStream Parties. Each OneStream Party, jointly and severally, represents and warrants to and agrees with each of the Underwriters that:

(A) the subject of any economic or trade sanctions administered or enforced by the United States Government (including the U.S. Department of the Treasury’s Office of Foreign Assets Control and the U.S. Department of State), the United Nations Security Council, the European Union, His Majesty’s Treasury, or any other relevant sanctions authority (collectively, “Sanctions”), or

(B) located, organized or resident in a country or territory that is the subject of comprehensive territorial Sanctions (including, without limitation, the so-called Donetsk People’s Republic, the so-called Luhansk People’s Republic, or any other Covered Region of Ukraine identified pursuant to Executive Order 14065, Crimea, Cuba, Iran, North Korea and Syria).

(ii) The OneStream Parties and the Subsidiaries have not, in violation of sanctions, engaged in, are not now engaged in, and will not engage in, any dealings or transactions with any

Person, or in any country or territory, that at the time of the dealing or transaction is or was, or whose government is or was, the subject of Sanctions.

(i) to fund or facilitate any activities or business of or with any Person or in any country or territory that, at the time of such funding or facilitation, is, or whose government is, the subject of Sanctions;

(ii) to fund or facilitate any money laundering or terrorist financing activities; or

(iii) in any other manner that would cause or result in a violation of any Anti-Corruption Laws, Anti-Money Laundering Laws, or Sanctions by any Person (including any Person participating in the offering, whether as underwriter, advisor, investor or otherwise).

2. Representations and Warranties of the Selling Stockholders. Each Selling Stockholder, severally and not jointly, represents and warrants to and agrees with each of the Underwriters that:

3. Agreements to Sell and Purchase. Each Seller, severally and not jointly, hereby agrees to sell to the several Underwriters, and each Underwriter, upon the basis of the representations and warranties herein contained, but subject to the terms and conditions hereinafter stated, agrees, severally and not jointly, to purchase from such Seller at $[ • ] a share (the “Purchase Price”) the number of Firm Shares (subject to such adjustments to eliminate fractional shares as Morgan Stanley may determine) that bears the same proportion to the number of Firm Shares to be sold by such Seller as the number of Firm Shares set forth in Schedule I hereto opposite the name of such Underwriter bears to the total number of Firm Shares.

On the basis of the representations and warranties contained in this Agreement, and subject to its terms and conditions, each Seller, severally and not jointly, agrees to sell to the Underwriters the Additional Shares, and the Underwriters shall have the right to purchase, severally and not jointly, up to [ • ] Additional Shares at the Purchase Price, provided, however, that the amount paid by the Underwriters for any Additional Shares shall be reduced by an amount per share equal to any dividends declared by the Company and payable on the Firm Shares but not payable on such Additional Shares. The Representatives may exercise this right on behalf of the Underwriters in whole or from time to time in part by giving written notice to the Company not later than 30 days after the date of this Agreement. Any exercise notice shall specify the number of Additional Shares to be purchased by the Underwriters and the date on which such Additional Shares are to be purchased. Each purchase date must be at least one business day after the written notice is given and may not be earlier than the closing date for the Firm Shares or later than ten business days after the date of such notice. On each day, if any, that Additional Shares are to be purchased (an “Option Closing Date”), each Underwriter agrees, severally and not jointly, to purchase the number of Additional Shares (subject to such adjustments to eliminate fractional shares as the Representatives may determine) that bears the same proportion to the total number of Additional Shares to be purchased on such Option Closing Date as the number of Firm Shares set forth in Schedule I hereto opposite the name of such Underwriter bears to the total number of Firm Shares.

4. Terms of Public Offering. The Sellers are advised by the Representatives that the Underwriters propose to make a public offering of their respective portions of the Shares as soon after the Registration Statement and this Agreement have become effective as in the Representatives’ judgment is advisable. The Sellers are further advised by the Representatives that the Shares are to be offered to the public initially at $[ • ] a share (the “Public Offering Price”) and to certain dealers selected by the Representatives at a price that represents a concession not in excess of $[ • ] a share under the Public Offering Price.

5. Payment and Delivery. Payment for the Firm Shares to be sold by each Seller shall be made to such Seller in federal or other funds immediately available in New York City against delivery of such Firm Shares for the respective accounts of the several Underwriters at 10:00 a.m., New York City time, on [ • ], 2024, or at such other time on the same or such other date, not later than [ • ], 2024, as shall be agreed upon in writing by the Company and the Representatives. The time and date of such payment are hereinafter referred to as the “Closing Date.”

Payment for any Additional Shares to be sold by each Seller shall be made to such Seller in federal or other funds immediately available in New York City against delivery of such Additional Shares for the respective accounts of the several Underwriters at 10:00 a.m., New York City time, on the date specified in the corresponding notice described in Section 3 or at such other time on the same or on such other date, in any event not later than [ • ], 2024, as shall be agreed upon in writing by the Company and the Representatives.

The Firm Shares and Additional Shares shall be registered in such names and in such denominations as the Representatives shall request in writing not later than one full business day prior to the Closing Date or the applicable Option Closing Date, as the case may be. The Firm Shares and Additional Shares shall be delivered to the Representatives on the Closing Date or an Option Closing Date, as the case may be, for the respective accounts of the several Underwriters. The Purchase Price payable by the Underwriters shall be reduced by (i) any transfer taxes paid by, or on behalf of, the Underwriters in connection with the transfer of the Shares to the Underwriters duly paid and (ii) any withholding required by law.

6. Conditions to the Underwriters’ Obligations. The obligations of the Sellers to sell the Shares to the Underwriters and the several obligations of the Underwriters to purchase and pay for the Shares on the Closing Date are subject to the condition that the Registration Statement shall have become effective not later than [ • ] p.m. (New York City time) on the date hereof.

The several obligations of the Underwriters are subject to the following further conditions:

(i) no order suspending the effectiveness of the Registration Statement shall be in effect, and no proceeding for such purpose or pursuant to Section 8A under the Securities Act shall be pending before or threatened by the Commission;

(ii) there shall not have occurred any downgrading, nor shall any notice have been given of any intended or potential downgrading or of any review for a possible change that does not indicate the direction of the possible change, in the rating accorded any of the securities of the Company or any of its Subsidiaries by any “nationally recognized statistical rating organization,” as such term is defined in Section 3(a)(62) of the Exchange Act; and

(iii) there shall not have occurred any change, or any development involving a prospective change, in the condition, financial or otherwise, or in the earnings, business or operations of the OneStream Parties and the Subsidiaries, taken as a whole, from that set forth in the Time of Sale Prospectus that, in the Representatives’ judgment, is material and adverse and that makes it, in the Representatives’ judgment, impracticable to market the Shares on the terms and in the manner contemplated in the Time of Sale Prospectus.

The officer signing and delivering such certificate may rely upon the best of his or her knowledge as to proceedings threatened.

With respect to the negative assurance letters to be delivered pursuant to Sections 6(c) and 6(j) above, Wilson Sonsini Goodrich & Rosati, Professional Corporation, and Latham & Watkins LLP may state that their opinions and beliefs are based upon their participation in the preparation of the Registration Statement, the Time of Sale Prospectus and the Prospectus and any amendments or supplements thereto and review and discussion of the contents thereof, but are without independent check or verification, except as specified. With respect to Section 6(d), 6(e), 6(f), 6(g), 6(h) and 6(i) above, Jones Day, Stikeman Elliot LLP, Whalen LLP and Maples, Calder (Cayman) LLP, Walkers (Cayman) LLP and Pinsent Masons LLP may rely upon an opinion or opinions of counsel for any Selling Stockholders and, with respect to factual matters and to the extent such counsel deems appropriate, upon the representations of each Selling Stockholder contained herein and in the Custody Agreement and Power of Attorney of such Selling Stockholder (as applicable) and in other documents and instruments; provided that (A) each such counsel for the Selling Stockholder is satisfactory to the Representatives, (B) a copy of each opinion so relied upon is delivered to the Representatives and is in form and substance satisfactory to the Representatives, (C) copies of such Custody Agreements and Powers of Attorney and of any such other documents and instruments shall be delivered to the Representatives and shall be in form and substance satisfactory to the Representatives and (D) Jones Day, Stikeman Elliot LLP, Whalen LLP, Maples and Calder (Cayman) LLP, Walkers (Cayman) LLP and Pinsent Masons LLP shall state in their opinion that they are justified in relying on each such other opinion.

(i) a certificate, dated the Option Closing Date and signed by an executive officer of each OneStream Party on behalf of such OneStream Party, confirming that the certificate delivered on the Closing Date pursuant to Section 6(b) hereof remains true and correct as of such Option Closing Date;

(ii) an opinion and negative assurance letter of Wilson Sonsini Goodrich & Rosati, Professional Corporation, outside counsel for the Company, dated the Option Closing Date, relating to the Additional Shares to be purchased on such Option Closing Date and otherwise to the same effect as the opinion and negative assurance letter required by Section 6(c) hereof;

(iii) an opinion of Jones Day, outside counsel for KKR, in their capacity as Selling Stockholders, dated the Option Closing Date, in form and substance reasonably satisfactory to the Representatives, relating to the Additional Shares to be purchased on such Option Closing Date and otherwise to the same effect as the opinion letter required by Section 6(d) hereof;

(iv) an opinion of Maples and Calder (Cayman) LLP, Cayman Islands special counsel to KKR TFO Partners L.P., KKR Custom Equity Opportunities Fund L.P., KKR-Milton Strategic Partners L.P., KKR NGT (Dream) Blocker Parent L.P., KKR NGT (Dream) Blocker Parent (EEA) L.P. and KKR Wolverine I Ltd., each of which is a KKR Seller identified on Schedule II hereto, in their capacity as a Selling Stockholder, dated the Option Closing Date, relating to the Additional Shares to be purchased on such Option Closing Date and otherwise to the same effect as the opinion letter required by Section 6(e) hereof;

(v) an opinion of Stikeman Elliot LLP, Ontario counsel to K-PRIME AG Financing L.P., a KKR Seller identified on Schedule II hereto, in their capacity as a Selling Stockholder, dated the Option Closing Date, relating to the Additional Shares to be purchased on such Option Closing Date and otherwise to the same effect as the opinion required by Section 6(f) hereof;

(vi) an opinion of Whalen LLP, outside counsel for the Selling Stockholders other than KKR and Alkeon, dated the Option Closing Date, relating to the Additional Shares to be purchased on such Option Closing Date and otherwise to the same effect as the opinion required by Section 6(g) hereof;

(vii) an opinion of Pinsent Masons LLP, outside counsel for Alkeon Lux, dated the Option Closing Date, relating to the Additional Shares to be purchased on such Option Closing Date and otherwise to the same effect as the opinion required by Section 6(h) hereof;

(viii) an opinion of Walkers (Cayman) LLP, outside counsel for Alkeon Innovation, dated the Option Closing Date, relating to the Additional Shares to be purchased on such Option Closing Date and otherwise to the same effect as the opinion required by Section 6(i) hereof;

(ix) an opinion and negative assurance letter of Latham & Watkins LLP, counsel for the Underwriters, dated the Option Closing Date, relating to the Additional Shares to be purchased on such Option Closing Date and otherwise to the same effect as the opinion and negative assurance letter required by Section 6(j) hereof;

(x) a letter dated the Option Closing Date, in form and substance satisfactory to the Underwriters, from Ernst & Young LLP, independent public accountants, substantially in the same form and substance as the letter furnished to the Underwriters

pursuant to Section 6(k) hereof; provided that the letter delivered on the Option Closing Date shall use a “cut-off date” not earlier than two business days prior to such Option Closing Date;

(xi) a Chief Financial Officer’s certificate, dated the Option Closing Date and signed on behalf of the Company by the Chief Financial Officer of the Company, in substantially the same form and substance as the certificate required by Section 6(l) hereof; and

(xii) such other documents as the Representatives may reasonably request with respect to the good standing of each OneStream Party, the due authorization and issuance of the Additional Shares to be sold on such Option Closing Date and other matters related to the issuance of such Additional Shares.

7. Covenants of the OneStream Parties. Each OneStream Party, jointly and severally, covenants with each Underwriter as follows:

Each OneStream Party covenants with each Underwriter that, without the prior written consent of the Representatives on behalf of the Underwriters, it will not, and will not publicly disclose an intention to, during the period ending 60 days after the date of the Prospectus (the “Restricted Period”), (1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option,

right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, or (2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise or (3) publicly file any registration statement with the Commission relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock.

The restrictions contained in the preceding paragraph shall not apply to (A) the Shares to be sold hereunder or the issuance, transfer, redemption or exchange of securities of the OneStream Parties in connection with the transactions contemplated by this Agreement as described in the Time of Sale Prospectus and the Prospectus, (B) the issuance of shares of Common Stock by the Company upon the exercise of an option or warrant, the conversion or vesting and settlement of a security outstanding on the date hereof, or the redemption or exchange of membership interests of OneStream LLC, as described in the Time of Sale Prospectus and the Prospectus; provided that each recipient of Common Stock pursuant to this clause (B) shall execute a lock-up agreement substantially in the form of Exhibit A hereto with respect to the remaining portion of the Restricted Period, (C) the grant of options or any other type of equity award described in the Time of Sale Prospectus and the Prospectus, or the issuance of shares of Common Stock by the Company (whether upon the exercise of stock options or otherwise) to employees, officers, directors, advisors or consultants of the Company pursuant to employee benefit plans in effect on the date hereof and described in the Time of Sale Prospectus and the Prospectus; provided that each recipient of Common Stock pursuant to this clause (C) shall execute a lock-up agreement substantially in the form of Exhibit A hereto with respect to the remaining portion of the Restricted Period, (D) the confidential submission of a registration statement; provided that no public announcements are made regarding the submission or transaction during the Restricted Period; (E) the filing by the Company of a registration statement on Form S-8 relating to the issuance, vesting, exercise or settlement of equity awards granted or to be granted pursuant to any employee benefit plan in effect on the date hereof and described in the Time of Sale Prospectus and the Prospectus, (F) the establishment of a trading plan on behalf of itself or a stockholder, officer or director of the Company pursuant to Rule 10b5-1 under the Exchange Act for the transfer of shares of Common Stock, provided that (i) such plan does not provide for the transfer of Common Stock during the Restricted Period (except to the extent otherwise allowed pursuant to the terms of the Lock-up Agreement) and (ii) to the extent a public announcement or filing under the Exchange Act, if any, is required of or voluntarily made by the Company regarding the establishment of such plan, such announcement or filing shall include a statement to the effect that no transfer of Common Stock may be made under such plan during the Restricted Period, or (G) the sale or issuance of or entry into an agreement to sell or issue Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock in connection with one or more mergers, acquisitions of securities, businesses, property or other assets, products or technologies; joint ventures; commercial relationships or other strategic corporate transactions or alliances; provided that the aggregate amount of Common Stock

or any securities convertible into or exercisable or exchangeable for Common Stock (on an as-converted, as-exercised or as-exchanged basis) that the Company may sell or issue or agree to sell or issue pursuant to this clause (G) shall not exceed 10% of the total number of shares of Common Stock of the Company issued and outstanding immediately following the completion of the transactions contemplated by this Agreement (including issuance of Additional Shares, if any) determined on a fully-diluted basis and assuming that all outstanding membership interests in OneStream LLC that are exchangeable for shares of Class A Common Stock are so exchanged.

8. Covenants of the Selling Stockholders. Each Selling Stockholder, severally and not jointly, covenants with each Underwriter as follows:

9. Expenses. Whether or not the transactions contemplated in this Agreement are consummated or this Agreement is terminated, the OneStream Parties, jointly and severally, agree to pay or cause to be paid all expenses incident to the performance of their obligations under this Agreement, including: (i) the fees, disbursements and expenses of the OneStream Parties’ counsel, the OneStream Parties’ accountants and counsel for the Selling Stockholders in connection with the registration and delivery of the Shares under the Securities Act and all other fees or expenses in connection with the preparation and filing of the Registration Statement, any preliminary prospectus, the Time of Sale Prospectus, the Prospectus, any free writing prospectus prepared by or on behalf of, used by, or referred to by any OneStream Party and amendments and supplements to any of the foregoing, including all printing costs associated therewith, and the mailing and delivering of copies thereof to the Underwriters and dealers, in the quantities hereinabove specified, (ii) all costs and expenses related to the transfer and delivery of the Shares to the Underwriters, including any transfer or other taxes payable thereon, (iii) the reasonable and documented cost of printing or producing any Blue Sky or Legal Investment memorandum in connection with the offer and sale of the Shares under state securities laws and all expenses in connection with the qualification of the Shares for offer and sale under state securities laws as provided in Section 7(g) hereof, including filing fees and the reasonable and documented fees and disbursements of counsel for the Underwriters in connection with such qualification and in connection with the Blue Sky or Legal Investment memorandum, (iv) all filing fees and the reasonable and documented fees and disbursements of counsel to the Underwriters incurred in

connection with the review and qualification of the offering of the Shares by FINRA (provided that the aggregate amount payable by the Company pursuant to clause (iii) and the reasonable and documented fees and disbursements of counsel to the Underwriters described in this clause (iv) shall not exceed $25,000) (v) the cost of printing certificates representing the Shares, (vi) the costs and charges of any transfer agent, registrar or depositary, (vii) the costs and expenses of the OneStream Parties relating to investor presentations on any road show undertaken in connection with the marketing of the offering of the Shares (with the Underwriters agreeing to pay all costs and expenses related to their participation in investor presentations on any road show undertaken in connection with the marketing of the offering of the Shares, including all travel, lodging and other expenses of the Underwriters or any of their employees), including, without limitation, expenses associated with the preparation or dissemination of any electronic road show, expenses associated with the production of road show slides and graphics, fees and expenses of any consultants engaged in connection with the road show presentations with the prior approval of the Company and travel and lodging expenses of the representatives and officers of the Company and any such consultants, (viii) the document production charges and expenses associated with printing this Agreement and (ix) all other costs and expenses incident to the performance of the obligations of the OneStream Parties hereunder for which provision is not otherwise made in this Section. It is understood, however, that except as provided in this Section, Section 11 entitled “Indemnity and Contribution” and the last paragraph of Section 14 below, the Underwriters will pay all of their costs and expenses, including fees and disbursements of their counsel, stock transfer taxes payable on resale of any of the Shares by them and any advertising expenses connected with any offers they may make.

The provisions of this Section shall not supersede or otherwise affect any agreement that the Sellers may otherwise have for the allocation of such expenses among themselves.

10. Covenants of the Underwriters. Each Underwriter, severally and not jointly, covenants with the OneStream Parties not to take any action that would result in the Company being required to file with the Commission under Rule 433(d) a free writing prospectus prepared by or on behalf of such Underwriter that otherwise would not be required to be filed by the Company thereunder, but for the action of the Underwriter.

11. Indemnity and Contribution. (a) The OneStream Parties agree, jointly and severally, to indemnify and hold harmless each Underwriter, each person, if any, who controls any Underwriter within the meaning of either Section 15 of the Securities Act or Section 20 of the Exchange Act, and each affiliate of any Underwriter within the meaning of Rule 405 under the Securities Act from and against any and all losses, claims, damages and liabilities (including, without limitation, any legal or other expenses reasonably incurred in connection with defending or investigating any such action or claim) that arise out of, or are based upon, any untrue statement or alleged untrue statement of a material fact contained in the Registration Statement or any amendment thereof, any preliminary prospectus, the Time of Sale Prospectus or any amendment or supplement thereto, any issuer free writing prospectus as defined in Rule 433(h) under the Securities Act, any OneStream Party information that any OneStream Party has filed, or is required

to file, pursuant to Rule 433(d) under the Securities Act, any “road show” as defined in Rule 433(h) under the Securities Act (a “road show”), the Prospectus or any amendment or supplement thereto, or any Testing-the-Waters Communication, or that arise out of, or are based upon, any omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, except insofar as such losses, claims, damages or liabilities that arise out of, or are based upon, any such untrue statement or omission or alleged untrue statement or omission made in reliance upon and in conformity with any information relating to any Underwriter furnished to the Company in writing by such Underwriter through the Representatives expressly for use therein, it being understood and agreed that the only such information furnished by the Underwriters through the Representatives consists of the Underwriter Information described as such in paragraph (c) below.

12. [Reserved]

13. Termination. The Underwriters may terminate this Agreement by notice given by the Representatives to the Company, if after the execution and delivery of this Agreement and prior to or on the Closing Date or any Option Closing Date, as the case may be, (i) trading generally shall have been suspended or materially limited on, or by, as the case may be, any of the New York Stock Exchange or the Nasdaq Global Select Market, (ii) trading of any securities of the Company shall have been suspended on any exchange or in any over‑the‑counter market, (iii) a material disruption in securities settlement, payment or clearance services in the United States shall have occurred, (iv) any moratorium on commercial banking activities shall have been declared by federal or New York State authorities or (v) there shall have occurred any outbreak or escalation of hostilities, or any change in financial markets or any calamity or crisis that, in the Representatives’ judgment, is material and adverse and which, singly or together with any other event specified in this clause (v), makes it, in the Representatives’ judgment, impracticable or inadvisable to proceed with the offer, sale or delivery of the Shares on the terms and in the manner contemplated in the Time of Sale Prospectus or the Prospectus.

14. Effectiveness; Defaulting Underwriters. This Agreement shall become effective upon the execution and delivery hereof by the parties hereto.

If, on the Closing Date or an Option Closing Date, as the case may be, any one or more of the Underwriters shall fail or refuse to purchase Shares that it has or they have agreed to purchase hereunder on such date, and the aggregate number of Shares which such defaulting Underwriter or Underwriters agreed but failed or refused to purchase is

not more than one‑tenth of the aggregate number of the Shares to be purchased on such date, the other Underwriters shall be obligated severally in the proportions that the number of Firm Shares set forth opposite their respective names in Schedule I bears to the aggregate number of Firm Shares set forth opposite the names of all such non‑defaulting Underwriters, or in such other proportions as the Representatives may specify, to purchase the Shares which such defaulting Underwriter or Underwriters agreed but failed or refused to purchase on such date; provided that in no event shall the number of Shares that any Underwriter has agreed to purchase pursuant to this Agreement be increased pursuant to this Section 14 by an amount in excess of one‑ninth of such number of Shares without the written consent of such Underwriter. If, on the Closing Date, any Underwriter or Underwriters shall fail or refuse to purchase Firm Shares and the aggregate number of Firm Shares with respect to which such default occurs is more than one‑tenth of the aggregate number of Firm Shares to be purchased on such date, and arrangements satisfactory to the Representatives, the Company and the Selling Stockholders for the purchase of such Firm Shares are not made within 36 hours after such default, this Agreement shall terminate without liability on the part of any non‑defaulting Underwriter, any OneStream Party or the Selling Stockholders. In any such case either the Representatives or the relevant Sellers shall have the right to postpone the Closing Date, but in no event for longer than seven days, in order that the required changes, if any, in the Registration Statement, in the Time of Sale Prospectus, in the Prospectus or in any other documents or arrangements may be effected. If, on an Option Closing Date, any Underwriter or Underwriters shall fail or refuse to purchase Additional Shares and the aggregate number of Additional Shares with respect to which such default occurs is more than one‑tenth of the aggregate number of Additional Shares to be purchased on such Option Closing Date, the non-defaulting Underwriters shall have the option to (i) terminate their obligation hereunder to purchase the Additional Shares to be sold on such Option Closing Date or (ii) purchase not less than the number of Additional Shares that such non-defaulting Underwriters would have been obligated to purchase in the absence of such default. Any action taken under this paragraph shall not relieve any defaulting Underwriter from liability in respect of any default of such Underwriter under this Agreement.

If this Agreement shall be terminated by the Underwriters, or any of them, because of any failure or refusal on the part of any OneStream Party or Seller to comply with the terms or to fulfill any of the conditions of this Agreement, or if for any reason any OneStream Party or Seller shall be unable to perform its obligations under this Agreement as a result of the circumstances described in Section 13(ii), the OneStream Parties will reimburse the Underwriters or such Underwriters as have so terminated this Agreement with respect to themselves, severally, for all out‑of‑pocket expenses (including the fees and disbursements of their counsel) reasonably incurred by such Underwriters in connection with this Agreement or the offering contemplated hereunder.

15. Entire Agreement. (a) This Agreement, together with any contemporaneous written agreements and any prior written agreements (to the extent not superseded by this Agreement) that relate to the offering of the Shares, represents the entire agreement between the OneStream Parties and the Selling Stockholders, on the one hand, and the Underwriters, on the other, with respect to the preparation of any

preliminary prospectus, the Time of Sale Prospectus, the Prospectus, the conduct of the offering, and the purchase and sale of the Shares.

16. Recognition of the U.S. Special Resolution Regimes. (a) In the event that any Underwriter that is a Covered Entity becomes subject to a proceeding under a U.S. Special Resolution Regime, the transfer from such Underwriter of this Agreement, and any interest and obligation in or under this Agreement, will be effective to the same extent as the transfer would be effective under the U.S. Special Resolution Regime if this Agreement, and any such interest and obligation, were governed by the laws of the United States or a state of the United States.

For purposes of this Section a “BHC Act Affiliate” has the meaning assigned to the term “affiliate” in, and shall be interpreted in accordance with, 12 U.S.C. § 1841(k).

“Covered Entity” means any of the following: (i) a “covered entity” as that term is defined in, and interpreted in accordance with, 12 C.F.R. § 252.82(b); (ii) a “covered bank” as that term is defined in, and interpreted in accordance with, 12 C.F.R. § 47.3(b); or (iii) a “covered FSI” as that term is defined in, and interpreted in accordance with, 12 C.F.R. § 382.2(b). “Default Right” has the meaning assigned to that term in, and shall be interpreted in accordance with, 12 C.F.R. §§ 252.81, 47.2 or 382.1, as applicable. “U.S. Special Resolution Regime” means each of (i) the Federal Deposit Insurance Act and the regulations promulgated thereunder and (ii) Title II of the Dodd-Frank Wall Street Reform and Consumer Protection Act and the regulations promulgated thereunder.

17. Counterparts. This Agreement may be signed in two or more counterparts, each of which shall be an original, with the same effect as if the signatures thereto and hereto were upon the same instrument. Counterparts may be delivered via facsimile, electronic mail (including any electronic signature covered by the U.S. federal ESIGN Act of 2000, Uniform Electronic Transactions Act, the Electronic Signatures and Records Act or other applicable law, e.g., www.docusign.com) or other transmission method and any counterpart so delivered shall be deemed to have been duly and validly delivered and be valid and effective for all purposes.

18. Applicable Law. This Agreement shall be governed by and construed in accordance with the internal laws of the State of New York.

19. Headings. The headings of the sections of this Agreement have been inserted for convenience of reference only and shall not be deemed a part of this Agreement.

20. Notices. All communications hereunder shall be in writing and effective only upon receipt and if to the Underwriters shall be delivered, mailed or sent the Representatives at Morgan Stanley & Co. LLC, 1585 Broadway, New York, New York 10036, Attention: Equity Syndicate Desk, with a copy to the Legal Department; J.P. Morgan Securities LLC, 383 Madison Avenue, New York, New York 10179 (fax: (212) 622-8358), Attention Equity Syndicate Desk; and KKR Capital Markets LLC, 30 Hudson Yards, New York, New York 10001; if to the OneStream Parties shall be delivered, mailed or sent to OneStream, Inc., 362 South Street, Rochester, Michigan 48307, Attention: General Counsel, with a copy to Wilson Sonsini Goodrich & Rosati, 650 Page Mill Road, Palo Alto, California 94303, Attention: Allison B. Spinner; if to KKR shall be delivered, mailed or sent to KKR Dream Holdings LLC, c/o Kohlberg Kravis Roberts & Co. L.P., 30 Hudson Yards, New York, NY 10001, Attention: General Counsel, with a copy to Jones Day, 1755 Embarcadero Road, Palo Alto, California 94303, Attention: Timothy Curry ***@***); and, if to the Selling Stockholders other than KKR shall be delivered, mailed or sent to each of the Attorneys-in-Fact named in the Power of Attorney, c/o the Company at the address set forth on the cover of the Registration Statement, Attention: General Counsel, with a copy, which shall not constitute notice, to Whalen LLP, 4701 Von Karman Av, Suite 325, Newport Beach, CA 92660.

21. Allocation of Selling Stockholder Securities. Without limiting the applicability of Section 3 hereof or any other provision of this Agreement, with respect to any Underwriter who is affiliated with any person or entity engaged to act as an investment adviser on behalf of an advisory client who has a direct or indirect interest in the Shares being sold by a Selling Stockholder, it is the intention of such Selling Stockholder that the Shares being sold to such Underwriter shall not include any Shares attributable to such client (with any such Shares instead being intended by such Selling Stockholder to be allocated and sold to the other Underwriters) and, accordingly, the fees or other amounts received by such Underwriter in connection with the transactions contemplated hereby shall not include any fees or other amounts attributable to such client (and, if there is any unsold allotment in the offering at the Closing Date, such unsold allotment in respect of Shares attributable to such client being intended by such Selling Stockholder shall be allocated solely to Underwriters not affiliated with such client).

[Signature Pages Follow]

SCHEDULE II

* KKR Seller

SCHEDULE III

Time of Sale Prospectus

Firm Shares to be sold by the Company: [ • ]

Firm Shares to be sold by the Selling Shareholders: [ • ]

Additional Shares to be sold by the Company: [ • ]

Additional Shares to be sold by the Selling Shareholders: [ • ]

Public Offering Price: $[ • ] per share

Underwriting Discount per Share: $[ • ]

SCHEDULE IV

Written Testing-the-Waters Communications

1. None.

EXHIBIT A

FORM OF LOCK-UP AGREEMENT

_____________, 2024

Morgan Stanley & Co. LLC

J.P. Morgan Securities LLC

as Representatives of the several

Underwriters listed in Schedule I to the

Underwriting Agreement referred to below

c/o Morgan Stanley & Co. LLC

1585 Broadway

New York, NY 10036

c/o J.P. Morgan Securities LLC

383 Madison Avenue

New York, NY 10179

Ladies and Gentlemen:

The undersigned understands that Morgan Stanley & Co. LLC and J.P. Morgan Securities LLC (collectively, the “Representatives”) propose to enter into an Underwriting Agreement (the “Underwriting Agreement”) with OneStream, Inc., a Delaware corporation (the “Company”), OneStream Software, LLC (“OneStream LLC”) and the selling stockholders named in the Underwriting Agreement, providing for the public offering (the “Public Offering”) by the several Underwriters listed on Schedule I to the Underwriting Agreement, including the Representatives (the “Underwriters”), of shares (the “Shares”) of the Class A common stock, par value $0.0001 per share, of the Company (the “Class A Common Stock”). The undersigned further understands that the Company is authorized to issue, in addition to Class A Common Stock, shares of Class B common stock (the “Class B Common Stock”), Class C common stock (the “Class C Common Stock”) and Class D common stock (together with the Class A Common Stock, Class B Common Stock and Class C Common Stock, the “Common Stock”).

To induce the Underwriters that may participate in the Public Offering to continue their efforts in connection with the Public Offering, the undersigned hereby agrees that, without the prior written consent of each of the Representatives on behalf of the Underwriters, the undersigned will not, and will not cause any of the undersigned’s direct or indirect affiliates to, and will not publicly disclose an intention to, during the period commencing on the date of this letter agreement (this “Letter Agreement”) and ending 60 days after the date of the final prospectus (the “Restricted Period”) related to the Public Offering (the “Prospectus”), (1) offer[, pledge,] sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, make any short sale or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or units of OneStream LLC

beneficially owned (as such term is used in Rule 13d-3 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”)), by the undersigned or any other securities so owned that are convertible into or exercisable or exchangeable (directly or indirectly) for, or that represent the right to receive, Common Stock or units of OneStream LLC (such shares of Common Stock, units of OneStream LLC or such other securities collectively, the “Securities,” and any such Securities beneficially owned by the undersigned, the “Undersigned’s Securities”), or (2) enter into any swap, hedging transaction or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Undersigned’s Securities, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of Securities, in cash or otherwise. The undersigned acknowledges and agrees that the foregoing precludes the undersigned from engaging in any hedging or other transactions or arrangements (including, without limitation, any short sale or the purchase or sale of, or entry into, any put or call option, or combination thereof, forward, swap or any other derivative transaction or instrument, however described or defined) designed or intended, or which could reasonably be expected to lead to or result in, a sale or disposition or transfer (whether by the undersigned or any other person) of any economic consequences of ownership, in whole or in part, directly or indirectly, of any of the Undersigned’s Securities, whether any such transaction or arrangement (or instrument provided for thereunder) would be settled by delivery of Securities, in cash or otherwise.

Notwithstanding the foregoing, the undersigned may transfer the Undersigned’s Securities in the following transactions:

(1) any sales of Common Stock by the undersigned to the Underwriters pursuant to the Underwriting Agreement;

(2) transactions relating to Securities acquired in the Public Offering or in open market transactions after the completion of the Public Offering, provided that no filing under Section 16(a) of the Exchange Act shall be required or shall be voluntarily made during the Restricted Period in connection with subsequent sales of Securities acquired in the Public Offering or such open market transactions;

(3) transfers of the Undersigned’s Securities (i) as a bona fide gift, (ii) for bona fide estate planning purposes, (iii) upon death or by will, testamentary document or intestate succession, (iv) to an immediate family member of the undersigned or to any trust for the direct or indirect benefit of the undersigned or the immediate family of the undersigned (for purposes of this clause (3), “immediate family” shall mean any spouse or domestic partner and relationship by blood, current or former marriage or domestic partnership, or adoption, not more remote than first cousin), or (v) if the undersigned is a trust, to any beneficiary of the undersigned or the estate of any such beneficiary;

(4) distributions, transfers or dispositions of the Undersigned’s Securities (i) to another corporation, partnership, limited liability company, trust or other business entity (or in each case its nominee or custodian) that is an affiliate (as defined in Rule 405 promulgated under the Securities Act) of the undersigned, or to any investment fund or other entity that controls, is controlled by, or is under common control with, or managed by the undersigned or affiliates of the undersigned, or (ii) as part of a distribution, transfer or disposition by the undersigned to its stockholders, current or former partners (general or limited), affiliates, subsidiaries, members, beneficiaries or other equity holders, or to the estates of any such stockholders, partners, beneficiaries or other equity holders;

(5) (i) the receipt by the undersigned from the Company of Securities upon the exercise of options or settlement of restricted stock units or other equity awards, or (ii) the transfer of Securities to the Company upon a vesting or settlement event of the Company’s restricted stock units or upon the exercise of options to purchase the Company’s securities on a “cashless” or “net exercise” basis to the extent permitted by the instruments representing such securities, options or restricted stock units (and any transfer to the Company necessary in respect of such amount needed for the payment of taxes, including estimated taxes, due as a result of such vesting, settlement or exercise whether by means of a “net settlement” or otherwise) so long as such “cashless” exercise or “net exercise” is effected solely by the surrender of outstanding securities, options or restricted stock units (or the Securities issuable upon the exercise or settlement thereof) to the Company and the Company’s cancellation of all or a portion thereof to pay the exercise price and/or withholding tax and remittance obligations, provided that (x) the Securities received upon exercise or settlement of the security, option or restricted stock unit are subject to the terms of this Letter Agreement, and (y) in the case of either clause (i) or (ii), any filing under Section 16(a) of the Exchange Act shall clearly indicate in the footnotes thereto that (A) the filing relates to the circumstances described in clauses (i) or (ii), as the case may be, (B) no Securities were sold by the reporting person and (C) in the case of clause (i), the Securities received upon exercise or settlement of the option or restricted stock unit are subject to a lock-up agreement with the Underwriters of the Public Offering;

(6) “sell-to-cover” transactions in connection with the exercise of options or vesting and settlement of restricted stock units pursuant to employee benefit plans (including equity incentive plans) described in the Prospectus, to satisfy applicable tax withholding obligations, provided that any filing under Section 16(a) of the Exchange Act shall clearly indicate in the footnote thereto that the filing relates to the circumstances described in this clause (6);

(7) the establishment or modification of a trading plan on behalf of a stockholder, officer or director of the Company pursuant to Rule 10b5-1 under the Exchange Act for the transfer of Securities (a “10b5-1 Plan”), provided that (i) such 10b5-1 Plan does not provide for the transfer of Securities during the Restricted Period and (ii) to the extent a public announcement or filing under the Exchange Act, if any, is required of or voluntarily made by or on behalf of the undersigned or the Company regarding the establishment or modification of such 10b5-1 Plan during the Restricted Period, such announcement or filing shall include a statement to the effect that no transfer of Securities may be made under such 10b5-1 Plan during the Restricted Period;

(8) sales of Securities under a 10b5-1 Plan that is existing as of the date hereof, provided that, if the undersigned is required to file a report under Section 16(a) of the Exchange Act during the Restricted Period, such filing shall state that such transaction has been executed under a 10b5-1 Plan and shall also state the date such 10b5-1 Plan was adopted;

(9) the transfer of Securities that occurs by operation of law pursuant to a qualified domestic order in connection with a divorce settlement, divorce decree, separation agreement or other court order or order of a regulatory agency, provided that such transfer shall not involve a disposition for value, and each such transferee shall sign and deliver a lock-up agreement substantially in the form of this Letter Agreement;

(10) without limiting clause (12) below, transfers, conversions, reclassifications, redemptions or exchanges of the Undersigned’s Securities in connection with the Public Offering, provided that any filing under Section 16(a) of the Exchange Act shall clearly indicate in the footnotes thereto the circumstances of such transfer, conversion, reclassification, redemption or exchange, and provided, further that any new Securities received upon such transfer, conversion, reclassification, redemption or exchange shall be subject to the terms of this Letter Agreement;

(11) the transfer of Securities in connection with or in response to a bona fide third-party tender offer, merger, consolidation or other similar transaction that is approved by the Board of Directors of the Company or OneStream LLC, made to all holders of the Company’s or OneStream LLC’s, as applicable, capital stock involving a Change of Control (as defined below), provided that in the event that the tender offer, merger, consolidation or other such transaction is not completed, the Undersigned’s Securities shall remain subject to the restrictions contained in this Letter Agreement (for purposes of this clause (9), “Change of Control” means the transfer (whether by tender offer, merger, consolidation or other similar transaction), in one transaction or a series of related transactions, to a person or group of affiliated persons (other than the Underwriters pursuant to the Public Offering), of Securities if, after such transfer, the equity holders of the Company or OneStream LLC, as applicable, immediately prior to such transfer do not own at least a majority of the outstanding voting securities of the Company (or the surviving entity) or OneStream LLC (or the surviving entity), as applicable;

(12) any sale or transfer of Securities to the Company or OneStream LLC as part of the Synthetic Secondary (as described in the Prospectus) or pursuant to other arrangements under which the undersigned or the Company has or will have the option or obligation to sell, purchase, repurchase, reclassify, redeem, convert or exchange such Securities or a right of first refusal with respect to such Securities;

(13) [transfers to permit lenders or finance counterparties (as well as any security agent, securities intermediary and/or custodian) in connection with a loan (including any margin loan) or other financing transaction provided to the undersigned and/or its affiliates to enforce their security interest by foreclosing, selling, transferring, appropriating or otherwise disposing of the Securities;] and

(14) transactions as permitted with the prior written consent of the Representatives;

provided that in the case of any transfer, distribution or disposition pursuant to clause (3)[ or (4)], such transfer shall not involve a disposition for value[; provided, further that in the case of any transfer, distribution or disposition pursuant to clause (3) or (4)], each transferee, donee or distributee shall sign and deliver a lock-up agreement substantially in the form of this Letter Agreement and any public announcement or filing under Section 16(a) of the Exchange Act, or any other public filing or disclosure reporting a reduction in beneficial ownership of shares of Common Stock, shall clearly indicate in the footnotes thereto the nature of the transaction; and provided, further that in the case of any transfer pursuant to clause (9) or (12), no public announcement or filing under Section 16(a) of the Exchange Act, or any other public filing or disclosure shall be made during the Restricted Period, unless such filing is required and clearly indicates in the footnotes thereto that it relates to the circumstances described in clauses (9) or (12), as the case may be.

In addition, the undersigned agrees that, without the prior written consent of the Representatives on behalf of the Underwriters, it will not, during the Restricted Period, make any demand or request for, or exercise any right with respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock, unless such demand or exercise shall not require the public filing of a registration statement until the expiration of the Restricted Period; provided that, a confidential submission of a registration statement shall be permitted so long as no public announcement is made regarding the submission or transaction during the Restricted Period. The undersigned also agrees and consents to the entry of stop transfer instructions with the Company’s transfer agent and registrar against the transfer of the undersigned’s shares of Common Stock except in compliance with the foregoing restrictions.

The undersigned understands that the Company and the Underwriters are relying upon this Letter Agreement in proceeding toward consummation of the Public Offering. The undersigned further understands that this Letter Agreement is irrevocable and shall be binding upon the undersigned’s heirs, legal representatives, successors and assigns.

In furtherance of the foregoing, the Company, and any duly appointed transfer agent for the registration or transfer of the securities described herein, are hereby authorized to decline to make any transfer of securities if such transfer would constitute a violation or breach of this Letter Agreement.

The undersigned hereby represents and warrants that the undersigned has full power and authority to enter into this Letter Agreement. All authority herein conferred or agreed to be conferred and any obligations of the undersigned shall be binding upon the successors, assigns, heirs or personal representatives of the undersigned.

The undersigned acknowledges and agrees that the Underwriters have not provided any recommendation or investment or other advice nor have the Underwriters solicited any action from the undersigned with respect to the Public Offering of the Shares and the undersigned has consulted their own legal, accounting, financial, regulatory, tax and other advisors with respect to this Letter Agreement and the subject matter thereof to the extent deemed appropriate. The undersigned

further acknowledges and agrees that, although the Underwriters may provide certain Regulation Best Interest and Form CRS disclosures or other related documentation to you in connection with the Public Offering, the Underwriters are not making a recommendation to you to participate in the Public Offering, enter into this Letter Agreement, or sell any Shares at the price determined in the Public Offering, and nothing set forth in such disclosures or documentation is intended to suggest that any Underwriter is making such a recommendation.

This Letter Agreement shall automatically terminate, and the undersigned will be released from all of his, her or its obligations hereunder, upon the earliest to occur, if any, of (a) the date that the Company advises the Representatives, in writing, prior to the execution of the Underwriting Agreement, that it has determined not to proceed with the Public Offering, (b) the date that the Company withdraws the registration statement related to the Public Offering before the execution of the Underwriting Agreement, (c) if the Underwriting Agreement is executed but terminated (other than the provisions thereof that survive termination) prior to payment for and delivery of the Shares to be sold thereunder, the date that the Underwriting Agreement is terminated or (d) December 31, 2024 if the Public Offering of the Shares has not been completed by such date.

Whether or not the Public Offering actually occurs depends on a number of factors, including market conditions. Any Public Offering will only be made pursuant to the Underwriting Agreement, the terms of which are subject to negotiation between the Company and the Underwriters.

This Letter Agreement may be delivered via facsimile, electronic mail (including any electronic signature covered by the U.S. federal ESIGN Act of 2000, Uniform Electronic Transactions Act, the Electronic Signatures and Records Act or other applicable law, e.g., www.docusign.com) or other transmission method and any signature so delivered shall be deemed to have been duly and validly delivered and be valid and effective for all purposes.

This Letter Agreement shall be governed by and construed in accordance with the laws of the State of New York.

[Signature page follows.]

Yours very truly,