Quest Diagnostics Inc

Item 1.01 Entry into a Material Definitive Agreement

On May 6, 2026, Quest Diagnostics Incorporated (the "Company") issued $500,000,000 aggregate principal amount of 5.000% senior notes due 2036 (the "Notes").

The Company will pay interest on the Notes on June 30 and December 30 of each year, beginning on December 30, 2026.

The Notes will mature on June 30, 2036. The Notes will be the senior unsecured obligations of the Company and will rank equally with the Company's other existing and future senior unsecured obligations. The Notes will not be entitled to the benefit of any sinking fund.

The Notes were issued pursuant to an indenture dated as of June 27, 2001 among the Company, the guarantors (as defined therein) and The Bank of New York Mellon, as trustee (the "Trustee"), as supplemented from time to time, and as further supplemented by a twenty-fourth supplemental indenture dated as of May 6, 2026 between the Company and the Trustee (collectively, the "Indenture"). The Indenture contains covenants that, among other things, will limit the ability of (i) the Company and certain of its subsidiaries to create certain liens and enter into certain sale and leaseback transactions and (ii) the Company to consolidate, merge or transfer all or substantially all of the Company's assets on a consolidated basis. The Indenture provides for customary events of default. Upon a change of control triggering event (as defined in the Indenture), the Company will be required to make an offer to purchase the Notes at a price equal to 101% of their principal amount plus accrued and unpaid interest to the repurchase date.

The foregoing description of the Indenture does not purport to be complete and is qualified in its entirety by reference to the text of the applicable agreements, each of which is included as an exhibit to this Current Report on Form 8-K and incorporated by reference herein.

Acopy of the opinion of Allen Overy Shearman Sterling US LLP, counsel to the Company, relating to the legality of the Notes is filed as Exhibit 5.1 to this Current Report on Form 8-K.

Item 9.01 Financial Statements and Exhibits

4.1 Indenture dated as of June 27, 2001, among the Company, the Subsidiary Guarantors and the Trustee (filed as an Exhibit to the Company's current report on Form 8-K (Date of Report: June 27, 2001) and incorporated herein by reference)

4.2* Twenty-Fourth Supplemental Indenture, dated as of May 6 , 2026, between the Company and the Trustee

4.3* Form of the Company's 5.000% Senior Note due 2036 (incorporated by reference from Exhibit A to Exhibit 4.2 hereof)

5.1* Opinion of Allen Overy Shearman Sterling US LLP, counsel to the Company

23.1* Consent of Allen Overy Shearman Sterling US LLP (included in Exhibit 5.1)

104* The cover page from this current report on Form 8-K, formatted in Inline XBRL.