Sec Form 4 Filing - Summit Partners Growth Equity Fund IX-A, L.P. @ LifeStance Health Group, Inc. - 2021-06-14

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

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1. Name and Address of Reporting Person Summit Partners Growth Equity Fund IX-A, L.P. 2. Issuer Name and Ticker or Trading Symbol LifeStance Health Group, Inc. [ LFST] 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) SUMMIT PARTNERS, 222 BERKELEY ST FL 18 3. Date of Earliest Transaction (MM/DD/YY) 06/14/2021 (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 Common Stock 06/14/2021 S 1,368,844 ( 1 ) D $ 17.01 46,875,407 ( 2 ) D ( 3 ) ( 4 )

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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Summit Partners Growth Equity Fund IX-A, L.P. SUMMIT PARTNERS, 222 BERKELEY ST FL 18 BOSTON, MA02116 X Summit Partners Growth Equity Fund IX-B, L.P. SUMMIT PARTNERS, 222 BERKELEY ST FL 18 BOSTON, MA02116 X SUMMIT INVESTORS GE IX/VC IV (UK), L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X SUMMIT INVESTORS GE IX/VC IV, LLC 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Summit Partners Entrepreneur Advisors Fund II, L.P. 222 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X Signatures Summit Partners Growth Equity Fund IX-A, L.P., by Summit Partners GE IX, L.P., its GP, by Summit Partners GE IX, LLC, its GP, by Summit Partners, L.P., its Manager, by Summit Master Company, LLC, its GP, by /s/ Robin W. Devereux, Member 06/16/2021 Signature of Reporting Person Date Summit Partners Growth Equity Fund IX-B, L.P., by Summit Partners GE IX, L.P., its GP, by Summit Partners GE IX, LLC, its GP, by Summit Partners, L.P., its Manager, by Summit Master Company, LLC, its GP, by /s/ Robin W. Devereux, Member 06/16/2021 Signature of Reporting Person Date Summit Investors GEIX/VC IV (UK), L.P., by Summit Investors Management, LLC, its General Partner, by Summit Master Company, LLC, its Managing Member, by Robin W. Devereux, Member 06/16/2021 Signature of Reporting Person Date Summit Investors GEIX/VC IV, LLC, by Summit Investors Management, LLC, its Manager, by Summit Master Company, LLC, its Managing Member, by Robin W. Devereux, Member 06/16/2021 Signature of Reporting Person Date Summit Partners Entrepreneur Advisors Fund II, L.P., by Summit Partners Entrepreneur Advisors GP II, LLC, its General Partner, by Robin W. Devereux, Member 06/16/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents 838,224 shares sold by Summit Partners Growth Equity Fund IX-A, L.P., 523,375 shares sold by Summit Partners Growth Equity Fund IX-B, L.P., 5,851 shares sold by Summit Investors GE IX/VC IV, LLC, 782 shares sold by Summit Partners Entrepreneur Advisors Fund II, L.P., and 612 shares sold by Summit Investors GE IX/VC IV (UK), L.P. ( 2 )Represents 28,704,562 shares held by Summit Partners Growth Equity Fund IX-A, L.P., 17,922,731 shares held by Summit Partners Growth Equity Fund IX-B, L.P., 200,368 shares held by Summit Investors GE IX/VC IV, LLC, 26,786 shares held by Summit Partners Entrepreneur Advisors Fund II, L.P., and 20,960 shares held by Summit Investors GE IX/VC IV (UK), L.P. ( 3 )Summit Partners, L.P. is the managing member of Summit Partners GE IX, LLC, which is general partner of Summit Partners GE IX, LP, which is the general partner of Summit Partners Growth Equity Fund IX-A, L.P. and Summit Partners Growth Equity Fund IX-B, L.P. Summit Master Company, LLC is (i) the sole member of Summit Partners Entrepreneur Advisors GP II, LLC, which is the general partner of Summit Partners Entrepreneur Advisors Fund II, L.P. and (ii) the general partner of Summit Partners L.P., which is the manager of Summit Investors Management, LLC, which is the manager of Summit Investors GE IX/VC IV, LLC, and the general partner of Summit Investors GE IX/VC IV (UK), L.P. ( 4 )Summit Master Company, LLC, as the sole member of Summit Partners Entrepreneur Advisors GP II, LLC and 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 responsible for voting and investment decisions with respect to LifeStance Health Group, Inc. Summit Partners, L.P., through a three-person investment committee, currently composed of Peter Y. Chung, Mark A. deLaar and Craig D. Frances, has voting and dispositive authority over the shares held by each of these entities and therefore beneficially owns such shares. Each of the Summit Funds, Mr. Chung, Mr. deLaar and Dr. Frances disclaim disclaims beneficial ownership of the shares, except, in each case, to the extent of such person's or entity's pecuniary interest therein.

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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