UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C.  20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported)

November 9, 2026

HA SUSTAINABLE INFRASTRUCTURE CAPITAL, INC.

(Exact Name of Registrant as Specified in its Charter)

One Park Place,

Suite 200

Annapolis, Maryland 21401

(Address of principal executive offices)

(Zip Code)

Registrant’s telephone number, including area code: (410) 571-9860

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Exchange Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging Growth Company ¨

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.   ¨

Item 8.01 Other Events

On November 9, 2026, HA Sustainable Infrastructure Capital, Inc. (the “Company”) and the Guarantors (as defined below) entered into an underwriting agreement (the “Junior Subordinated Notes Underwriting Agreement”) with Mizuho Securities USA LLC, BofA Securities, Inc., Goldman Sachs & Co. LLC and Truist Securities, Inc., as representatives of the several underwriters (the “Underwriters”), pursuant to which the Company agreed to issue and sell to the Underwriters $500 million aggregate principal amount of its 7.850% Green Junior Subordinated Notes due 2057 (the “Junior Subordinated Notes”), in accordance with the terms and conditions set forth in the Junior Subordinated Notes Underwriting Agreement. The Junior Subordinated Notes will be sold at a public offering price of 100% of the aggregate principal amount thereof.

At issuance, the Junior Subordinated Notes will be guaranteed on a subordinated basis by Hannon Armstrong Sustainable Infrastructure, L.P., Hannon Armstrong Capital, LLC, HAT Holdings I LLC, HAT Holdings II LLC, HAC Holdings I LLC, and HAC Holdings II LLC (collectively, the “Guarantors”). The closing of the offering of Junior Subordinated Notes is expected to occur on November 24, 2026, subject to customary closing conditions. The Company intends to use the net proceeds from the offering to (i) temporarily repay a portion of the outstanding borrowings under the Company’s standalone commercial paper program and (ii) potentially temporarily repay a portion of the outstanding borrowings under the Company’s unsecured credit facility or the Company’s credit-enhanced commercial paper program. The Company will use cash equal to the net proceeds from the offering of the Junior Subordinated Notes to acquire, invest in or refinance, in whole or in part, new and/or existing eligible green projects. These eligible green projects may include projects with disbursements made during the twelve months preceding the issue date of the offering of the Junior Subordinated Notes and projects with disbursements to be made within two years following the issue date. Prior to the full investment of an amount equal to such net proceeds in such eligible green projects, the Company intends to apply the net proceeds as set forth above and to invest any remaining net proceeds in interest-bearing accounts and short-term, interest-bearing securities.

The sale of the Junior Subordinated Notes has been registered with the Securities and Exchange Commission (the “Commission”) in a registration statement on Form S-3ASR, File No. 333-285461 (the “Registration Statement”). The terms of the Junior Subordinated Notes are described in the base prospectus included in the Registration Statement, as supplemented by a preliminary prospectus supplement dated November 9, 2026 and a final prospectus supplement dated November 9, 2026.

The preceding description is qualified in its entirety by reference to the Junior Subordinated Notes Underwriting Agreement, a copy of which is attached as Exhibit 1.1 to this Current Report on Form 8-K and is incorporated herein by reference.

Item 9.01 Financial Statements and Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.