6-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

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

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of November 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

As previously disclosed, on November 13, 2025, Nyxoah SA (the “Company”) entered into a securities purchase agreement (the “Purchase Agreement”) with certain investors (the “RDO Investors”), including certain institutional investors, pursuant to which the Company agreed to issue and sell, in a registered direct offering by the Company directly to the RDO Investors (the “Registered Direct Offering”), 1,215,964 ordinary shares, no nominal value per share, of the Company (the “Ordinary Shares”) to the RDO Investors, at a price of $4.6304 per share, for aggregate gross proceeds to the Company of approximately $5.6 million before deducting related offering expenses.

A copy of the legal opinion and consent of NautaDutilh BV/SRL relating to the validity of the issuance and sale of the Ordinary Shares  is attached as Exhibit 5.1 hereto and is incorporated by reference herein.

The informationcontained in this Report, including Exhibit 5.1 hereto, is hereby incorporated by reference into the Company’s registrationstatements on Form S-8 (Registration Numbers333-285960,333-261233and333-269410)and Form F-3 (Registration Numbers333-285982and333-268955)of the Company (including any prospectuses forming a part of such registration statements) and is a part thereof from the date onwhich this report is filed, to the extent not superseded by documents or reports subsequently filed or furnished.

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 5.1

Ladies and Gentlemen,

We have acted as Belgian legal counsel to Nyxoah SA, a limited liability company organized and existing under the laws of the Kingdom of Belgium, with its statutory seat at rue Edouard Belin 12, 1435 Mont-Saint-Guibert, and registered under company number 0817.149.675 (the "Company") on certain legal matters of Belgian law in connection with the preparation and filing of Company’s registration statement (the “RegistrationStatement”) on Form F-3, including all amendments or supplements thereto, filed by the Company with the United States Securities and Exchange Commission (the “SEC”) on November 22, 2022, under the United States Securities Act of 1933, as amended (the “Securities Act”), the prospectus dated January 6, 2023, which forms a part of and is included in the Registration Statement, and the prospectus supplement to be filed with the SEC (the “Prospectus Supplement”) in respect of the Company’s proposed offering in the context of a registered direct offering directly to investors in the United States of America of ordinary shares of the Company (the "Offer Shares") covered by the Registration Statement to which this opinion is an exhibit (the "Transaction"). The Offer Shares will comprise of 1,215,964 new ordinary shares with no nominal value per share to be issued by the Company pursuant to a capital increase to be resolved by the board of directors of the Company on or around 18 November 2025.

This opinion letter is solely given for the information of the Addressee. It may only be relied upon in connection with the Registration Statement by the Addressee and by the purchasers to which the Offer Shares have been allocated as part of the Transaction. This opinion letter is strictly limited to the matters stated in it and may not be read as extending by implication to any matters not specifically referred to in it. Nothing in this opinion letter should be taken as expressing an opinion in respect of any representations or warranties, or other information, contained in any document.

The section headings used in this opinion letter are for convenience or reference only and are not to affect its construction or be taken into consideration in its interpretation.

This opinion letter sets out our opinion on certain matters of the laws of Belgium with general applicability, and, insofar as they are directly applicable in Belgium, of the laws of the European Union, as at today's date and as presently interpreted under published authoritative case law of Belgian courts, the General Court and the Court of Justice of the European Union. Unless otherwise specifically stated herein, we do not express any opinion on tax law, on public international law or on the rules promulgated under or by any treaty organisation, except insofar as such rules are directly applicable in Belgium, nor do we express any opinion on Belgian or European competition law. No undertaking is assumed on our part to revise, update or amend this opinion letter in connection with or to notify or inform you of, any developments and/or changes to the laws of Belgium and of the European Union subsequent to today’s date.

As Belgian lawyers we are not qualified or able to assess the true meaning and purport of the terms of the Registration Statement and the Securities Purchase Agreement under any applicable law other than Belgian law and the obligations of the parties thereto, and we have made no investigation of such meaning and purport. Our review of the Registration Statement, the Prospectus Supplement and the Securities Purchase Agreement, has therefore been limited to the terms of such documents as they appear to us on their face.

In this opinion letter, legal concepts are expressed in English terms. The Belgian legal concepts concerned may not be identical in meaning to the concepts described by the English terms as they exist under the law of other jurisdictions. In the event of a conflict or inconsistency, the relevant expression shall be deemed to refer only to the Belgian legal concepts described by the English terms. As far as the word "non-assessable" used in this opinion letter is concerned, this word has no legal meaning under the laws of Belgium and is used in this opinion letter only to mean that, with respect to the issuance of the Offer Shares of the Company, (i) the initial purchaser of the Offer Shares will have no obligation to pay to the Company any additional amount in excess of the subscription price and (ii) the holders of the Offer Shares will not be liable, solely because of their status as a holder of the Offer Shares, for additional calls of funds on the Offer Shares by the Company or its creditors.

In rendering the opinions expressed herein, we have exclusively reviewed and relied upon the documents set out in Exhibit A to this opinion letter (the "Documents"), together with such other publicly available documents as we have considered it necessary or desirable. We have not investigated or verified any factual matter disclosed to us in the course of our review, nor do we opine on the accuracy of representations and warranties contained in documents reviewed by us.

The opinions expressed in this opinion letter are to be construed and interpreted in accordance with Belgian law. The competent courts at Brussels, Belgium have exclusive jurisdiction to settle any issues of interpretation or liability arising out of or in connection with this opinion letter and all matters related to the legal relationship between yourself and NautaDutilh BV/SRL, as well as between the purchasers of the Offer Shares and NautaDutilh BV/SRL, including the above submission to jurisdiction, are governed by Belgian law and the general terms and conditions of NautaDutilh BV/SRL^1^.

ASSUMPTIONS

For the purposes of this opinion letter, we have assumed that:

^1^ The applicable general terms and conditions of NautaDutilh BV/SRL can be found at all times at www.nautadutilh.com.

OPINION

Based upon and subject to the foregoing and subject to any matters, documents or events not disclosed to us, we express the following opinion:

*

We consent to the filing of this opinion as an exhibit to the Registration Statement and to the reference to us under the heading "Legal Matters" in the Prospectus Supplement, which is part of the Registration Statement. In giving this consent, we do not concede that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the SEC thereunder.

Yours faithfully,

/s/ NautaDutilh BV/SRL

NautaDutilh BV/SRL

exhibitA

Listof documents