Exhibit 4.3

SUPPLEMENTAL INDENTURE

Supplemental Indenture (this “Supplemental Indenture”), dated as of December 19, 2025, among MPSAB, LLC, a Delaware limited liability company (the “Guaranteeing Subsidiary”), a subsidiary of Millrose Properties, Inc., a Maryland corporation (the “Issuer”), the Issuer and Citibank, N.A., as the Trustee (the “Trustee”).

W I T N E S S E T H

WHEREAS, the Issuer and the Subsidiary Guarantors party thereto have heretofore executed and delivered to the Trustee an indenture (the “Indenture”), dated as of August 7, 2025, providing for the issuance of an unlimited aggregate principal amount of 6.375% Senior Notes due 2030 (the “Notes”);

WHEREAS, Section 4.16 of the Indenture provides that under certain circumstances the Guaranteeing Subsidiary shall execute and deliver to the Trustee a supplemental indenture pursuant to which the Guaranteeing Subsidiary shall unconditionally Guarantee all of the Issuer’s Obligations under the Notes and the Indenture on the terms and conditions set forth herein and under the Indenture; and

WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee is authorized to execute and deliver this Supplemental Indenture.

NOW THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt of which is hereby acknowledged, the parties mutually covenant and agree for the equal and ratable benefit of the Holders as follows:

1.Capitalized Terms. Capitalized terms used herein without definition shall have the meanings assigned to them in the Indenture.

2.Subsidiary Guarantor. The Guaranteeing Subsidiary hereby agrees to be a Subsidiary Guarantor under the Indenture and to be bound by the terms of the Indenture applicable to Subsidiary Guarantors, including Article 10 thereof.

3.Governing Law. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

4.Waiver of Jury Trial. EACH OF THE ISSUER, THE GUARANTEEING SUBSIDIARY AND THE TRUSTEE HEREBY IRREVOCABLY WAIVES, TO THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW, ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL PROCEEDING ARISING OUT OF OR RELATING TO THIS SUPPLEMENTAL INDENTURE, THE INDENTURE, THE NOTES, THE NOTE GUARANTEES OR THE TRANSACTIONS CONTEMPLATED HEREBY OR THEREBY.

5.Counterparts. The parties may sign any number of copies of this Supplemental Indenture. Each signed copy shall be an original, but all of them together represent the same agreement. The exchange of copies of this Supplemental Indenture and of signature pages by facsimile or .PDF transmission shall constitute effective execution and delivery of this Supplemental Indenture as to the parties hereto and may be used in lieu of the original Indenture for all purposes. Signatures of the parties hereto transmitted by facsimile or .PDF shall be deemed to be their original signatures for all purposes.

6.Headings. The headings of the Sections of this Supplemental Indenture have been inserted for convenience of reference only, are not to be considered a part of this Supplemental Indenture and shall in no way modify or restrict any of the terms or provisions hereof.

7.The Trustee. The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Supplemental Indenture or for or in respect of the recitals contained herein, all of which recitals are made solely by the Guaranteeing Subsidiary and the Issuer.

[Signature Page Follows]

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IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed, all as of the date first above written.

MPSAB, LLC, a Delaware liability company By: Millrose Properties SPE LLC, a Delaware limited liability company, its sole member By: Millrose Properties, Inc., a Maryland corporation, its sole member
By:	/s/ Darren L. Richman
	Name:	Darren Richman
	Title:	Chief Executive Officer and President
MILLROSE PROPERTIES, INC.
By:	/s/ Darren L. Richman
	Name:	Darren Richman
	Title:	Chief Executive Officer and President
CITIBANK, N.A., as Trustee
By:	/s/ Kari-anne Marshall
	Name:	Kari-anne Marshall
	Title:	Senior Trust Officer

[Signature Page to Supplemental Indenture]