LifeStance Health Group, Inc.

1. Represents 2,642,291 shares sold by Summit Partners Growth Equity Fund IX-A, L.P., 1,649,809 shares sold by Summit Partners Growth Equity Fund IX-B, L.P., 18,444 shares sold by Summit Investors GE IX/VC IV, LLC, 2,466 shares sold by Summit Partners Entrepreneur Advisors Fund II, L.P. and 1,929 shares sold by Summit Investors GE IX/VC IV (UK), L.P.

2. The reported securities are held as follows: 17,886,858 shares in the name of Summit Partners Growth Equity Fund IX-A, L.P.; 11,168,308 shares in the name of Summit Partners Growth Equity Fund IX-B, L.P.; 124,857 shares in the name of Summit Investors GE IX/VC IV, LLC; 16,691 shares in the name of Summit Partners Entrepreneur Advisors Fund II, L.P.; and 13,062 shares in the name of Summit Investors GE IX/ VC IV (UK), L.P.

3. Darren Black is a Managing Director and Member of Summit Master Company, LLC, the general partner of Summit Partners, L.P. 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 managing member 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, Darren M. Black 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. Black and Dr. Frances disclaim beneficial ownership of the shares, except, in each case, to the extent of such person's or entity's pecuniary interest therein.