8-K

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

Dateof Report (Date of earliest event reported): December 8, 2025

SOLUNA

HOLDINGS, INC.

(Exactname of Registrant as Specified in Its Charter)

Registrant’sTelephone Number, Including Area Code: (516) 216-9257

N/A

(FormerName 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 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. ☐

Item7.01 Regulation FD Disclosure.

On December 8, 2025, Soluna Holdings, Inc. issued a press release announcing the closing of its previously announced registered direct offering priced at-the-market under Nasdaq rules for the purchase and sale of 18,079,144 shares of common stock (or pre-funded warrants in lieu thereof) and accompanying Series C warrants to purchase up to 18,079,144 shares of common stock at a purchase price of $1.77 per share (or pre-funded warrant in lieu thereof) and accompanying Series C warrant. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated by reference herein.

Theinformation in Item 7.01 and in Exhibit 99.1 will not be treated as “filed” for the purposes of Section 18 of the SecuritiesExchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section. This informationwill not be incorporated by reference into any filing under the Securities Act of 1933 or into another filing under the Exchange Act,unless that filing expressly incorporates this information by reference.

Item9.01 Financial Statements and Exhibits.

(d) Exhibits.

SIGNATURES

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

Exhibit 99.1

SolunaAnnounces Closing of $32 Million Registered Direct Offering Priced At-The-Market Under Nasdaq Rules

ALBANY,NY — December 8, 2025 — Soluna Holdings, Inc. (“Soluna” or the “Company”) (NASDAQ: SLNH), a developer of green data centers for intensive computing applications, today announced the closing of its previously announced registered direct offering priced at-the-market under Nasdaq rules for the purchase and sale of 18,079,144 shares of common stock (or pre-funded warrants in lieu thereof) and accompanying Series C warrants to purchase up to 18,079,144 shares of common stock at a purchase price of $1.77 per share (or pre-funded warrant in lieu thereof) and accompanying Series C warrant. The Series C warrants have an exercise price of $1.65 per share, are exercisable immediately upon issuance, and will expire five years following the date of issuance.

H.C. Wainwright & Co. acted as the exclusive placement agent for the offering.

The gross proceeds of the offering described above were approximately $32 million before deducting placement agent fees and other offering expenses payable by the Company. The Company intends to use the net proceeds of the offering for working capital, project-level equity, and general corporate purposes.

The sale of the securities described above was made pursuant to the Company’s registration statement on Form S-3 (File No. 333-286638), including a base prospectus, filed with the Securities and Exchange Commission (“SEC”) and declared effective by the SEC on April 29, 2025, and a prospectus supplement filed with the SEC on December 5, 2025. Copies of the final prospectus supplement and the accompanying base prospectus may be obtained for free at the SEC’s EDGAR website at http://www.sec.gov. Additionally, copies of the final prospectus supplement and the accompanying base prospectus may be obtained by contacting H.C. Wainwright & Co., LLC at 430 Park Avenue, 3rd Floor, New York, NY 10022, by phone at (212) 856-5711 or e-mail at placements@hcwco.com.

This press release does not constitute an offer to sell or the solicitation of an offer to buy these securities, nor shall there be any sale of these securities in any jurisdiction in which such offer, solicitation, or sale would be unlawful prior to the registration or qualification under the securities laws of any such jurisdiction.

SafeHarbor Statement

All statements in this press release that are not historical are forward-looking statements. These statements are not historical facts but rather are based on the Company’s current expectations, estimates, and projections regarding its business, operations, and other similar or related factors. Words such as “may,” “will,” “could,” “would,” “should,” “anticipate,” “predict,” “potential,” “continue,” “expect,” “intend,” “plan,” “project,” “believe,” “estimate,” and other similar or elated expressions are used to identify these forward-looking statements, although not all forward-looking statements contain these words. You should not place undue reliance on forward-looking statements because they involve known and unknown risks, uncertainties, and assumptions that are difficult or impossible to predict and, in some cases, beyond the Company’s control. Actual results may differ materially from those in the forward-looking statements as a result of a number of factors, including those described in the Company’s filings with the SEC. The Company undertakes no obligation to revise or update information in this release to reflect events or circumstances in the future, even if new information becomes available.

AboutSoluna Holdings, Inc. (Nasdaq: SLNH)

Soluna is on a mission to make renewable energy a global superpower, using computing as a catalyst. The Company designs, develops, and operates digital infrastructure that transforms surplus renewable energy into global computing resources. Soluna’s pioneering data centers are strategically co-located with wind, solar, or hydroelectric power plants to support high-performance computing applications, including Bitcoin Mining, Generative AI, and other compute-intensive applications. Soluna’s proprietary software MaestroOS(™) helps energize a greener grid while delivering cost-effective and sustainable computing solutions and superior returns. To learn more, visit solunacomputing.com and follow us on:

LinkedIn: https://www.linkedin.com/company/solunaholdings/

X (formerly Twitter): x.com/solunaholdings

YouTube: youtube.com/c/solunacomputing

Newsletter: bit.ly/solunasubscribe

Resource Center: solunacomputing.com/resources

Soluna regularly posts important information on its website and encourages investors and potential investors to consult the Soluna investor relations and investor resources sections of its website regularly.

Contact

Public Relations

West of Fairfax for Soluna

Soluna@westof.co