X0202 SCHEDULE 13G/A 0001140361-22-005071 0001034196 XXXXXXXX LIVE 3 Class A Common Stock, $0.001 par value 03/31/2026 0001861795 Definitive Healthcare Corp. 24477E103 492 Old Connecticut Path, Suite 401 Framingham X1 01701 Rule 13d-1(d) Advent International, L.P. b DE 0.00 62493676.00 0.00 62493676.00 62493676.00 59.82 PN The reported percentage is calculated based on 104,472,371 shares of Class A common stock ("Common Stock") outstanding as of February 23, 2026, as reported on the Issuer's 10-K filed with the Securities and Exchange Commission ("SEC") on February 26, 2026. Advent International GP, LLC b DE 0.00 62493676.00 0.00 62493676.00 62493676.00 59.82 OO The reported percentage is calculated based on 104,472,371 shares of Common Stock outstanding as of February 23, 2026, as reported on the Issuer's 10-K filed with the SEC on February 26, 2026. Advent International GPE IX Limited Partnership b E9 16955510.00 0.00 16955510.00 0.00 16955510.00 16.23 PN The reported percentage is calculated based on 104,472,371 shares of Common Stock outstanding as of February 23, 2026, as reported on the Issuer's 10-K filed with the SEC on February 26, 2026. Advent International GPE IX-H Limited Partnership b E9 5428915.00 0.00 5428915.00 0.00 5428915.00 5.20 PN The reported percentage is calculated based on 104,472,371 shares of Common Stock outstanding as of February 23, 2026, as reported on the Issuer's 10-K filed with the SEC on February 26, 2026. Definitive Healthcare Corp. 492 Old Connecticut Path, Suite 401, Framingham, MA 01701 This statement is being jointly filed by each of the persons below pursuant to Rule 13d-1(k) promulgated by the SEC pursuant to Section 13 of the Act, all of whom together are referred to herein as the "Reporting Persons": (i) Advent International, L.P., a Delaware limited partnership; (ii) Advent International GP, LLC, a Delaware limited liability company; (iii) Advent International GPE IX Limited Partnership, a Cayman Islands limited partnership; and (iv) Advent International GPE IX-H Limited Partnership, a Cayman Islands limited partnership; Prudential Tower, 800 Boylston Street, Boston, MA 02199 See responses to row 4 on each cover page. Y See responses to row 9 on each cover page. The reported securities are directly held by the following: (i) 16,955,510 shares of Class A common stock held by Advent International GPE IX Limited Partnership; (ii) 3,359,809 shares of Class A common stock held by Advent International GPE IX-B Limited Partnership; (iii) 1,394,766 shares of Class A common stock held by Advent International GPE IX-C Limited Partnership; (iv) 1,463,380 shares of Class A common stock held by Advent International GPE IX-F Limited Partnership; (v) 4,815,226 shares of Class A common stock held by Advent International GPE IX-G Limited Partnership; (vi) 5,428,915 shares of Class A common stock held by Advent International GPE IX-H Limited Partnership; (vii) 3,075,053 shares of Class A common stock held by Advent International GPE IX-I Limited Partnership; (viii) 4,985,850 shares of Class A common stock held by Advent International GPE IX-A SCSP; (ix) 1,061,241 shares of Class A common stock held by Advent International GPE IX-D SCSP; (x) 2,156,723 shares of Class A common stock held by Advent International GPE IX-E SCSP; (xi) 97,427 shares of Class A common stock held by Advent Partners GPE IX Strategic Investors SCSP; (xii) 55,642 shares of Class A common stock held by Advent Partners GPE IX Limited Partnership; (xiii) 128,669 shares of Class A common stock held by Advent Partners GPE IX-A Limited Partnership; (xiv) 321,070 shares of Class A common stock held by Advent Partners GPE IX-C Limited Partnership (f/k/a Advent Partners GPE IX Cayman Limited Partnership); (xv) 54,121 shares of Class A common stock held by Advent Partners GPE IX Cayman Limited Partnership; (xvi) 898,507 shares of Class A common stock held by Advent Partners GPE IX-B Cayman Limited Partnership (the funds set forth in the foregoing clauses (i)-(xvi), the "Advent GPE IX Funds"); (xvii) 3,818,770 shares of Class A common stock held by Advent Global Technology Limited Partnership; (xviii) 2,971,879 shares of Class A common stock held by Advent Global Technology-B Limited Partnership; (xix) 1,609,070 shares of Class A common stock held by Advent Global Technology-C Limited Partnership; (xx) 1,926,387 shares of Class A common stock held by Advent Global Technology-D Limited Partnership; (xxi) 1,885,069 shares of Class A common stock held by Advent Global Technology-A SCSP; (xxii) 31,561 shares of Class A common stock held by Advent Partners AGT Limited Partnership; (xxiii) 27,373 shares of Class A common stock held by Advent Partners AGT-A Limited Partnership; (xxiv) 317,329 shares of Class A common stock held by Advent Partners AGT-C Limited Partnership (f/k/a Advent Partners AGT-Cayman Limited Partnership); (xxv) 30,542 shares of Class A common stock held by Advent Global Technology Strategic Investors Limited Partnership (the funds set forth in the following clauses (xvii)-(xxv), the "Advent Global Technology Funds"); and (xxvi) 3,623,787 shares of Class A common stock held by Advent Global Opportunities Master Limited Partnership (f/k/a Sunley House Capital Master Limited Partnership). Advent International GPE IX, LLC indirectly controls the general partner or manager, as applicable, of each of the Advent GPE IX Funds. Advent Global Technology LLC indirectly controls the general partner or manager, as applicable, of each of the Advent Global Technology Funds. Advent Global Opportunities GP LLC and Advent Global Opportunities Management LLC are the general partner and investment manager, respectively, of Advent Global Opportunities Master Limited Partnership. Advent International GP, LLC is the general partner of Advent International, L.P., and Advent International, L.P. is the manager of Advent International GPE IX, LLC and Advent Global Technology LLC, and is the sole member of Advent Global Opportunities GP LLC and Advent Global Opportunities Management LLC. Accordingly, each of Advent International GP, LLC and Advent International, L.P. may be deemed to have voting and dispositive power over the shares directly held by the Advent GPE IX Funds, the Advent Global Technology Funds, and Advent Global Opportunities Master Limited Partnership. Pursuant to Rule 13d-4 of the Act, the Reporting Persons declare that filing this statement shall not be construed as an admission that any of the Reporting Persons are beneficial owners of the reported securities, for the purposes of Section 13(d) and/or Section 13(g) of the Act. See responses to row 11 on each cover page. See responses to row 5 on each cover page. See responses to row 6 on each cover page. See responses to row 7 on each cover page. See responses to row 8 on each cover page. Y Y Y Y Y Y 99.1 Joint Filing Agreement, dated May 13, 2026 99.2 Signature Page, dated May 13, 2026 Advent International, L.P. /s/ Neil Crawford 05/13/2026 Advent International GP, LLC /s/ Neil Crawford 05/13/2026 Advent International GPE IX Limited Partnership /s/ Neil Crawford 05/13/2026 Advent International GPE IX-H Limited Partnership /s/ Neil Crawford 05/13/2026