Sec Form 3 Filing - SUMMIT PARTNERS L P @ Solo Brands, Inc. - 2021-10-28

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 SUMMIT PARTNERS L P 2. Issuer Name and Ticker or Trading Symbol Solo Brands, Inc. [ DTC] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 222 BERKELEY STREET, 18TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 10/28/2021 (Street) BOSTON, MA02116 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ 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, $0.001 par value per share 29,867,378 I See Footnote ( 1 ) ( 2 ) Class B Common Stock, $0.001 par value per share 14,167,582 I See Footnote ( 3 )

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 ( 3 ) ( 3 ) ( 3 ) Class A Common Stock 14,167,582 I See Footnote ( 3 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other SUMMIT PARTNERS L P 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Summit Partners Growth Equity Fund X-A, L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Summit Partners Growth Equity Fund X-B, L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Summit Partners Growth Equity Fund X-C, L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X SUMMIT INVESTORS X, LLC 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X SUMMIT INVESTORS X (UK), L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Summit Partners Subordinated Debt Fund V-A, L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Summit Partners Subordinated Debt Fund V-B, L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X SP-SS AGGREGATOR LLC 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Signatures /s/ Adam H. Hennessey, as attorney-in-fact for Summit Partners, L.P. 10/28/2021 Signature of Reporting Person Date /s/ Adam H. Hennessey, as attorney-in-fact for Summit Partners Growth Equity Fund X-A, L.P. 10/28/2021 Signature of Reporting Person Date /s/ Adam H. Hennessey, as attorney-in-fact for Summit Partners Growth Equity Fund X-B, L.P. 10/28/2021 Signature of Reporting Person Date /s/ Adam H. Hennessey, as attorney-in-fact for Summit Partners Growth Equity Fund X-C, L.P. 10/28/2021 Signature of Reporting Person Date /s/ Adam H. Hennessey, as attorney-in-fact for Summit Partners Subordinated Debt Fund V-A, L.P. 10/28/2021 Signature of Reporting Person Date /s/ Adam H. Hennessey, as attorney-in-fact for Summit Partners Subordinated Debt Fund V-B, L.P. 10/28/2021 Signature of Reporting Person Date /s/ Adam H. Hennessey, as attorney-in-fact for Summit Investors X, LLC 10/28/2021 Signature of Reporting Person Date /s/ Adam H. Hennessey, as attorney-in-fact for Summit Investors X (UK), L.P. 10/28/2021 Signature of Reporting Person Date /s/ Adam H. Hennessey, as attorney-in-fact for SP-SS Aggregator LLC 10/28/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents 11,304,941, 17,271,224, 466,295, 569,102, 201,182, 50,735, and 3,899 shares of Class A common stock held directly by Summit Partners Growth Equity Fund X-A, L.P., Summit Partners Growth Equity Fund X-B, L.P., Summit Partners Growth Equity Fund X-C, L.P., Summit Partners Subordinated Debt Fund V-A, L.P., Summit Partners Subordinated Debt Fund V-B, L.P., Summit Investors X, LLC, and Summit Investors X (UK), L.P., respectively. Summit Partners, L.P. is the managing member of Summit Partners GE X, LLC, which is the general partner of Summit Partners GE X, L.P., the general partner of each of Summit Partners Growth Equity Fund X-A, L.P., Summit Partners Growth Equity Fund X-B, L.P., and Summit Partners Growth Equity Fund X-C, L.P. Summit Partners, L.P. also is the managing member of Summit Partners SD V, LLC, which is the general partner of Summit Partners SD V, L.P., ( 2 )(continued from footnote 1) the general partner of each of Summit Partners Subordinated Debt Fund V-A, L.P. and Summit Partners Subordinated Debt Fund V-B, L.P. Summit Master Company, LLC is the sole managing member of Summit Investors Management, LLC, which is (A) the manager of Summit Investors X, LLC, and (B) the general partner of Summit Investors X (UK), L.P. Summit Master Company, LLC, as the managing member of Summit Investors Management, LLC, has delegated investment decisions, including voting and dispositive power, to Summit Partners, L.P. and its Investment Committee. ( 3 )Represents shares of Class B common stock (and associated common membership interests in Solo Stove Holdings, LLC ("Common Units")) held directly by SP-SS Aggregator LLC. SP-SS Aggregator LLC is managed by a manager appointed by the members holding a majority of the interests of the entity, which manager is currently designated to be Summit Partners Growth Equity Fund X-A, L.P. Shares of Class B common stock of the Issuer confer no economic rights on the holders thereof. Holders of shares of Class B common stock will be entitled to one vote per share on all matters to be voted on by holders of the Issuer's shares of Class A common stock. Upon exchange of Common Units reported in Table II hereof, an equal number of shares of Class B common stock will be delivered to the Issuer and cancelled for no consideration. Common Units do not expire.

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