SCHEDULE 13G/A 0000830588 XXXXXXXX LIVE 2 Common Stock, par value $0.01 per share 09/30/2025 0001845257 LifeStance Health Group, Inc 53228F101 4800 N. Scottsdale Road Suite 2500 Scottsdale AZ 85251 Rule 13d-1(d) Summit Partners, L.P. DE 0 33524715 0 33524715 33524715 N 8.62 PN Calculated based on 389,000,281 shares of common stock, par value $0.01 per share ("Common Stock") outstanding as of October 29, 2025, as reported on the Issuer's Form 10-Q, filed with the Securities and Exchange Commision ("SEC") on November 6, 2025. Summit Partners Growth Equity Fund IX-A, L.P. DE 0 20529149 0 20529149 20529149 N 5.28 PN Calculated based on 389,000,281 shares of Common Stock as of October 29, 2025, as reported on the Issuer's Form 10-Q, filed with the SEC on November 6, 2025. Summit Partners Growth Equity Fund IX-B, L.P. DE 0 12818117 0 12818117 12818117 N 3.30 PN Calculated based on 389,000,281 shares of Common Stock as of October 29, 2025, as reported on the Issuer's Form 10-Q, filed with the SEC on November 6, 2025. Summit Investors GE IX/VC IV (UK), L.P. E9 0 14991 0 14991 14991 N 0.01 PN Calculated based on 389,000,281 shares of Common Stock as of October 29, 2025, as reported on the Issuer's Form 10-Q, filed with the SEC on November 6, 2025. Summit Partners Entrepreneur Advisors Fund II, L.P. DE 0 19157 0 19157 19157 N 0.01 PN Calculated based on 389,000,281 shares of Common Stock as of October 29, 2025, as reported on the Issuer's Form 10-Q, filed with the SEC on November 6, 2025. Summit Investors GE IX/VC IV, LLC DE 0 143301 0 143301 143301 N 0.04 OO Calculated based on 389,000,281 shares of Common Stock as of October 29, 2025, as reported on the Issuer's Form 10-Q, filed with the SEC on November 6, 2025. LifeStance Health Group, Inc 4800 N. Scottsdale Road, Suite 6000 Scottsdale, Arizona 85251 This statement is filed by the entities and persons listed below, all of whom together are referred to herein as the "Reporting Persons": (i) Summit Partners, L.P.; (ii) Summit Partners Growth Equity Fund IX-A, L.P.; (iii) Summit Partners Growth Equity Fund IX-B, L.P.; (iv) Summit Investors GE IX/VC IV (UK), L.P.; (v) Summit Partners Entrepreneur Advisors Fund II, L.P.; and (vi) Summit Investors GE IX/VC IV, LLC 222 Berkeley Street, 18th Floor Boston, MA 02116 See response to Item 4 on each cover page Y See responses to Item 9 on each cover page. See responses to Item 11 on each cover page. See responses to Item 5 on each cover page. See responses to Item 6 on each cover page. See responses to Item 7 on each cover page. See response to Item 8 on each cover page. Summit Partners, L.P. is the managing member of Summit Partners GE IX, LLC, which is general partner of Summit Partners GE IX, L.P., 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. Summit Master Company, LLC, as the sole member of Summit Partners Entrepreneur Advisors GP II, LLC, the managing member of Summit Investors Management, LLC and general partner of Summit Partners, L.P., 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 the reported securities held by Summit Partners, L.P., through a four-person investment committee. Peter Y. Chung, Darren M. Black, Mark A. deLaar and Craig D. Frances are the current members of the investment committee, and as such may be deemed to have voting and dispositive authority over the reported securities, but each of the foregoing disclaim such beneficial ownership. This Statement shall not be construed as an admission that the Reporting Persons or any of the members of the investment committee are, for the purpose of Section 13(d) or 13(g) of the Exchange Act, the beneficial owner of any securities covered by this Statement. Y Y Y Y Y Y Summit Partners, L.P. By: Summit Master Company, LLC / /s/ Adam H. Hennessey, as POA 11/13/2025 Summit Partners Growth Equity Fund IX-A, L.P. By: Summit Partners GE IX, L.P. / /s/ Adam H. Hennessey, as POA 11/13/2025 Summit Partners Growth Equity Fund IX-B, L.P. By: Summit Partners GE IX, L.P. / /s/ Adam H. Hennessey, as POA 11/13/2025 Summit Investors GE IX/VC IV (UK), L.P. By: Summit Investors Management, LLC / /s/ Adam H. Hennessey, as POA 11/13/2025 Summit Partners Entrepreneur Advisors Fund II, L.P. By: Summit Investors Management, LLC / /s/ Adam H. Hennessey, as POA 11/13/2025 Summit Investors GE IX/VC IV, LLC By: Summit Partners Entrepreneur Advisors GP II, LLC / /s/ Adam H. Hennessey, as POA 11/13/2025 Exhibit A: Joint Filing Agreement, dated as of February 4, 2022, incorporated herein by reference to of the statement on Schedule 13G filed by the Reporting Persons on February 4, 2022. Exhibit B: Powers of Attorney, dated as of October 25, 2021, incorporated herein by reference to of the statement on Schedule 13G filed by the Reporting Persons on February 4, 2022.