6-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form6-K

REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TORULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of September 2025

Commission File Number: 001-40552

NYXOAH SA

(Translation of registrant’s name into English)

Rue Edouard Belin 12, 1435 Mont-Saint-Guibert,Belgium

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F x Form 40-F ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ¨

Note: Regulation S-T Rule 101(b)(1) only permits the submission in paper of a Form 6-K if submitted solely to provide an attached annual report to security holders.

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ¨

Note: Regulation S-T Rule 101(b)(7) only permits the submission in paper of a Form 6-K if submitted to furnish a report or other document that the registrant foreign private issuer must furnish and make public under the laws of the jurisdiction in which the registrant is incorporated, domiciled or legally organized (the registrant’s “home country”), or under the rules of the home country exchange on which the registrant’s securities are traded, as long as the report or other document is not a press release, is not required to be and has not been distributed to the registrant’s security holders, and, if discussing a material event, has already been the subject of a Form 6-K submission or other Commission filing on EDGAR.

Nyxoah SA

On September 5, 2025, Nyxoah SA (the “Company”) issued a press release, a copy of which is attached hereto as Exhibit 99.1.

The information in the attached Exhibit 99.1is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934,as amended (the “Exchange Act”), or otherwise subject to the liabilities of that Section, nor shall it be deemed incorporatedby reference in any filing made by the Company under the Securities Act of 1933, as amended, or the Exchange Act, except as otherwiseset forth herein or as shall be expressly set forth by specific reference in such a filing.

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, thereunto duly authorized.

Exhibit 99.1

REGULATED INFORMATION

Publicationrelating to transparency notifications

Mont-Saint-Guibert (Belgium), September 5,2025, 10:30 pm CET / 4:30 pm ET – In accordance with article 14 of the Act of 2 May 2007 on the disclosure of large shareholdings, Nyxoah SA (Euronext Brussels/Nasdaq: NYXH) announces that it received a transparency notification as detailed below.

On September 4, 2025, Nyxoah received a transparency notification from Cochlear Limited and Cochlear Investments Pty Ltd following a passive crossing of a threshold. Based on the notification, Cochlear Investments Pty Ltd holds 5,631,319 voting rights, representing 14.999% of the total number of voting rights on August 29, 2025 (37,544,782).

The notification dated September 4, 2025 contains the following information:

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Contact:

Nyxoah

John Landry, CFO

IR@nyxoah.com

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