6-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

Report of Foreign Private Issuer

Pursuant to Rule 13a-16 or 15d-16 of

the Securities Exchange Act of 1934

September 22, 2025

NEBIUS GROUP N.V.

Schiphol Boulevard 165

1118 BG, Schiphol, the Netherlands.

Tel: +31 202 066 970

(Address, Including ZIP Code, and Telephone Number,

Including Area Code, of Registrant’s Principal Executive Offices)

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 ¨

INFORMATION CONTAINED IN THIS REPORT ON FORM 6-K

Furnished as Exhibit 99.1 to this Report on Form 6-K is the press release by Nebius Group N.V. (the “Company”) announcing the exercise of the underwriters’ option to purchase an additional 1,621,621 Class A shares in the Company’s previously announced underwritten public offering at the offering price of $92.50, less underwriting discounts and commissions.

INCORPORATION BY REFERENCE

This Report on Form 6-K (excluding Exhibit 99.1) is hereby incorporated by reference into the Company’s Registration Statements on Form F-3ASR (File No. 333-286932) and Form S-8 (File No. 333-286934), including any prospectuses forming a part of such Registration Statements, to the extent not superseded by documents or reports subsequently filed or furnished.

INDEX TO 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

Nebius Group announces exercise of the underwriters’option to purchase additional Class A shares

Amsterdam,September 22, 2025—Nebius Group N.V. (“Nebius Group” or the “Company”; NASDAQ: NBIS), a leading AI infrastructure company, today announced that, in connection with its previously announced underwritten public offering of Class A ordinary shares, the underwriters have exercised in full their option to purchase an additional 1,621,621 Class A shares at the offering price of $92.50, less underwriting discounts and commissions, bringing Nebius’s aggregate gross proceeds from the Class A offering to approximately $1.15 billion. The initial closing of the Class A offering occurred on September 15, at which time the Company also closed its offering of convertible notes due 2030 and 2032 to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended. The aggregate proceeds of both offerings, including the proceeds of the additional Class A shares acquired upon exercise of the underwriters’ option, is approximately $4.3 billion.

Goldman Sachs & Co. LLC acted as lead book-running manager for the offering. Morgan Stanley, BofA Securities and Citigroup acted as additional book-running managers.

The Class A shares have been offered by the Company pursuant to its automatically effective shelf registration statement on Form F-3ASR filed with the U.S. Securities Exchange Commission (the “SEC”) on May 2, 2025, by means of a final prospectus supplement and an accompanying prospectus. A copy of the final prospectus supplement and the accompanying prospectus relating to the public offering has been filed with the SEC and may be obtained for free on the SEC’s website at http://www.sec.gov or by contacting the offices of Goldman Sachs & Co. LLC, Attention: Prospectus Department, 200 West Street, New York, NY 10282, by telephone at 1-866-471-2526 or email at prospectus-ny@ny.email.gs.com; the offices of Morgan Stanley & Co. LLC, Attention: Prospectus Department, 180 Varick Street, 2nd Floor, New York, NY 10014, by email at prospectus@morganstanley.com; the offices of BofA Securities, NC1-022-02-25, 201 North Tryon Street, Charlotte, NC 28255-0001, Attention: Prospectus Department, by email at dg.prospectus_requests@bofa.com; or the offices of Citigroup, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717, at prospectus@citi.com.

This press release does not and shall notconstitute an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale securities in any stateor other jurisdiction in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securitieslaws of any such state or other jurisdiction. Any offer, if at all, for any Class A shares of the Company will be made only by meansof the prospectus supplement and accompanying prospectus forming a part of the effective registration statement.

About Nebius Group

Nebius Group is a technology company building full-stack infrastructure to service the high-growth global AI industry. Headquartered in Amsterdam and listed on Nasdaq, Nebius Group has a global footprint with R&D hubs across Europe, North America and Israel.

Nebius Group’s AI-native cloud platform has been built for intensive AI workloads. With a full stack of purposefully designed and tuned proprietary software and hardware designed in-house, Nebius Group gives AI builders the compute, storage, managed services and tools they need to build, tune and run their models and applications.

Nebius Group also has additional businesses that operate under their own distinctive brands:

Nebius Group also holds equity stakes in other businesses including ClickHouse and Toloka.

Contacts

‍Investor Relations askIR@nebius.com

‍Media Relations media@nebius.com

Disclaimer

The Company has filed a registration statement (including a prospectus) with the SEC for the offering of the Company’s Class A shares to which this communication relates. Before you invest, you should read the prospectus in that registration statement and other documents the Company has filed with the SEC for more complete information about the issuer and this offering. You may get these documents for free by visiting the Company’s investor relations website and on the SEC website at https://www.sec.gov. Alternatively, the Company, any underwriter or any dealer participating in the offering of the Company’s Class A shares will arrange to send you the prospectus if you request it by emailing at prospectus-ny@ny.email.gs.com, prospectus@morganstanley.com or dg.prospectus_requests@bofa.com or prospectus@citi.com.

Forward LookingStatements

This press release contains forward-lookingstatements within the meaning of the Private Securities Litigation Reform Act of 1995, which involve risks and uncertainties. All statementscontained in this press release other than statements of historical facts, including, without limitation, statements regarding our futurefinancial and business performance, our business and strategy, expected growth, planned investments and capital expenditures, capacityexpansion plans, anticipated future financing transactions and expected financial results, are forward-looking statements. The words “anticipate,” “believe,” “continue,” “estimate,” “expect,” “guide,” “intend,” “likely,” “may,” “will” and similar expressions and their negatives are intended to identify forward-lookingstatements.

These forward-looking statements are subjectto risks, uncertainties and assumptions, some of which are beyond our control. Actual results may differ materially from the results predictedor implied by such statements, and our reported results should not be considered as an indication of future performance. The potentialrisks and uncertainties that could cause actual results to differ from the results predicted or implied by such statements include, amongothers: market conditions, our ability to build our businesses to the desired scale, competitive pressures, technological developments,our ability to secure and retain clients, our ability to secure additional capital to accommodate the growth of the business, unpredictablesales cycles, potential pricing pressures, as well as those risks and uncertainties related to our continuing businesses included underthe captions “Risk Factors” and “Operating and Financial Review and Prospects” in our Annual Report on Form 20-Ffor the year ended December 31, 2024, filed with the Securities and Exchange Commission (“SEC”) on April 30, 2025.All information in this press release is as of September 22, 2025 (unless stated otherwise). Except as required by law, we undertakeno obligation to update or revise publicly any forward-looking statements, whether as a result of new information, future events or otherwise,after the date on which the statements are made or to reflect the occurrence of unanticipated events.

In addition, statements that “we believe”and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information availableto us as of the date of this press release, and while we believe such information forms a reasonable basis for such statements, such informationmay be limited or incomplete, and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, orreview of, all potentially available relevant information. These statements are inherently uncertain, and investors are cautioned notto unduly rely upon these statements.