SCHEDULE 13G

CUSIP No.

1

Names of Reporting Persons

Advent International, L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)

(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 62,493,676.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 62,493,676.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

62,493,676.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

Checkbox not checked

11

Percent of class represented by amount in row (9)

59.82 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: 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.

SCHEDULE 13G

CUSIP No.

1

Names of Reporting Persons

Advent International GP, LLC

2

Check the appropriate box if a member of a Group (see instructions)

(a)

(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 62,493,676.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 62,493,676.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

62,493,676.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

Checkbox not checked

11

Percent of class represented by amount in row (9)

59.82 %

12

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person: 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.

SCHEDULE 13G

CUSIP No.

1

Names of Reporting Persons

Advent International GPE IX Limited Partnership

2

Check the appropriate box if a member of a Group (see instructions)

(a)

(b)

3

Sec Use Only

4

Citizenship or Place of Organization

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 16,955,510.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 16,955,510.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

16,955,510.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

Checkbox not checked

11

Percent of class represented by amount in row (9)

16.23 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: 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.

SCHEDULE 13G

CUSIP No.

1

Names of Reporting Persons

Advent International GPE IX-H Limited Partnership

2

Check the appropriate box if a member of a Group (see instructions)

(a)

(b)

3

Sec Use Only

4

Citizenship or Place of Organization

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 5,428,915.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 5,428,915.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

5,428,915.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

Checkbox not checked

11

Percent of class represented by amount in row (9)

5.20 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: 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.

SCHEDULE 13G

Item 1.

(a)

Name of issuer:

Definitive Healthcare Corp.

(b)

Address of issuer's principal executive offices:

492 Old Connecticut Path, Suite 401, Framingham, MA 01701

Item 2.

(a)

Name of person filing:

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;

(b)

Address or principal business office or, if none, residence:

Prudential Tower, 800 Boylston Street, Boston, MA 02199

(c)

Citizenship:

See responses to row 4 on each cover page.

(d)

Title of class of securities:

Class A Common Stock, $0.001 par value

(e)

CUSIP No.:

Item 3.

If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a)

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);

(b)

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);

(c)

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);

(d)

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);

(e)

An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);

(f)

An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);

(g)

A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);

(h)

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:

(k)

Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).

Item 4.

Ownership

(a)

Amount beneficially owned:

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.

(b)

Percent of class:

See responses to row 11 on each cover page.

(c)

Number of shares as to which the person has:

(i) Sole power to vote or to direct the vote:

See responses to row 5 on each cover page.

(ii) Shared power to vote or to direct the vote:

See responses to row 6 on each cover page.

(iii) Sole power to dispose or to direct the disposition of:

See responses to row 7 on each cover page.

(iv) Shared power to dispose or to direct the disposition of:

See responses to row 8 on each cover page.

Item 5.

Ownership of 5 Percent or Less of a Class.

Not Applicable

Item 6.

Ownership of more than 5 Percent on Behalf of Another Person.

Not Applicable

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.

Not Applicable

Item 8.

Identification and Classification of Members of the Group.

Not Applicable

Item 9.

Notice of Dissolution of Group.

Not Applicable

Item 10.

Certifications:

Not Applicable

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Advent International, L.P.

Signature:	/s/ Neil Crawford
Name/Title:	Neil Crawford / Vice President of Finance, See Exhibit 99.2
Date:	05/13/2026

Advent International GP, LLC

Signature:	/s/ Neil Crawford
Name/Title:	Neil Crawford / Vice President of Finance
Date:	05/13/2026

Advent International GPE IX Limited Partnership

Signature:	/s/ Neil Crawford
Name/Title:	Neil Crawford / Vice President of Finance, See Exhibit 99.2
Date:	05/13/2026

Advent International GPE IX-H Limited Partnership

Signature:	/s/ Neil Crawford
Name/Title:	Neil Crawford / Vice President of Finance, See Exhibit 99.2
Date:	05/13/2026

Exhibit Information

99.1 Joint Filing Agreement, dated May 13, 2026 99.2 Signature Page, dated May 13, 2026