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 UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of December 2025

Commission File Number: 001-41369

Osisko Development Corp. (Translation of registrant's name into English)

1100 Avenue des Canadiens-de-Montréal, Suite 300, Montréal, Quebec H3B 2S2 (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 [   ]      Form 40-F [ X ]

EXHIBIT INDEX

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

OSISKO DEVELOPMENT AND ELECTRIC ELEMENTSFILE EARLY WARNING REPORT FOR NIOBAY METALS INC.

Montreal, Québec, December 23, 2025 – Osisko DevelopmentCorp. (NYSE: ODV, TSXV: ODV) ("Osisko Development" or the "Company") announces that, on December 18, 2025, Osisko Development acquired, indirectly through its wholly-owned subsidiary, Barkerville Gold Mines Ltd. ("BGM"), 8,571,429 units of Niobay Metals Inc. ("Niobay") at a price of $0.14 per unit for an aggregate subscription price of $1,200,000.06, pursuant to a private placement completed by Niobay (the "Offering"). Each unit consisted of one common share of Niobay (each, a "Common Share") and one Common Share purchase warrant of Niobay (each, a "Warrant").

Immediately prior to the Offering, Osisko Development owned or controlled: (i) indirectly through its wholly-owned subsidiary, BGM, 9,857,143 Common Shares, representing approximately 7.4% of the issued and outstanding Common Shares on a basic basis; and (ii) together with Electric Elements Mining Corp. ("EEM"), a joint actor of ODV and BGM, an additional 4,615,400 Common Shares, representing approximately 3.5% of the issued and outstanding on a basic basis.

Accordingly, immediately prior to the Offering, Osisko Development owned or controlled, indirectly through its wholly-owned subsidiary, BGM, together with EEM, a joint actor of ODV and BGM, an aggregate of 10.8% of the issued and outstanding Common Shares on a basic basis (based on there being 133,468,560 Common Shares issued and outstanding at that time).

Immediately after the Offering, Osisko Development owned or controlled: (i) indirectly through its wholly-owned subsidiary, BGM, 18,428,572 Common Shares and 8,571,429 Warrants, representing approximately (a) 9.9% of the issued and outstanding Common Shares on a basic basis, and (b) 13.8% of the issued and outstanding Common Shares on a partially diluted basis (assuming, for this purpose, only the exercise in full of the Warrants); and (ii) together with EEM, a joint actor of ODV and BGM, an additional 4,615,400 Common Shares, representing approximately 2.5% of the issued and outstanding Common Shares on a basic basis.

Accordingly, immediately after the Offering, Osisko Development owned or controlled, indirectly through its wholly-owned subsidiary, BGM, together with EEM, a joint actor of ODV and BGM, an aggregate of 12.3% of the issued and outstanding Common Shares on a basic basis and 16.2% of the issued and outstanding Common Shares on a partially diluted basis (assuming, for this purpose, only the exercise in full of the Warrants).

An early warning report in respect of Niobay will be filed by Osisko Development, BGM and EEM with applicable Canadian securities regulatory authorities and will be available on SEDAR+ (www.sedarplus.ca) under the Niobay's issuer profile. To obtain copies of the early warning report filed by Osisko Development, BGM and EEM, please contact Philip Rabenok, telephone: (437) 423-3644.

The securities were acquired by Osisko Development for investment purposes. Osisko Development and its affiliates or any joint actors may, from time to time and at any time, acquire additional Common Shares and/or other equity, debt or other securities or instruments of Niobay (collectively, "Securities") in the open market or otherwise, and reserves the right to dispose of any or all of its Securities in the open market or otherwise at any time and from time to time, and to engage in similar transactions with respect to the Securities, the whole depending on market conditions, the business and prospects of Niobay and other relevant factors.

| www.osiskodev.com | Page 1 of 2 |

| --- | --- | | ABOUT OSISKO DEVELOPMENT CORP.<br><br><br><br><br><br><br><br>Osisko Development Corp. is a continental North American gold<br>development company focused on past-producing mining camps located in mining friendly jurisdictions with district scale potential. The<br>Company's objective is to become an intermediate gold producer by advancing its flagship permitted 100%-owned Cariboo Gold Project, located<br>in central B.C., Canada. Its project pipeline is complemented by the Tintic Project in the historic East Tintic mining district in Utah,<br>U.S.A.—brownfield properties with significant exploration potential, extensive historical mining data, access to existing infrastructure<br>and skilled labour. The Company's strategy is to develop attractive, long-life, socially and environmentally responsible mining assets,<br>while minimizing exposure to development risk and growing mineral resources.<br><br><br><br><br><br>For further information, visit our website<br>at www.osiskodev.com or contact: | | --- | | Sean Roosen | Philip Rabenok | | --- | --- | | Chairman and CEO | Vice President, Investor Relations | | Email: sroosen@osiskodev.com | Email: prabenok@osiskodev.com | | Tel: +1 (514) 940-0685 | Tel: +1 (437) 423-3644 |

CAUTION REGARDING FORWARD-LOOKING STATEMENTS

This news release contains "forward-looking information" (within the meaning of applicable Canadian securities laws) and "forward- looking statements" (within the meaning of the U.S. Private Securities Litigation Reform Act of 1995). Such statements in this news release may include, Osisko Development's objective and current strategy. Such forward-looking information or statements are based on a number of risks, uncertainties and assumptions which may cause actual results or other expectations to differ materially from those anticipated and which may prove to be incorrect. Although Osisko Development believes that the expectations reflected in the forward-looking information or statements are reasonable, prospective investors in Osisko Development securities should not place undue reliance on forward-looking statements because Osisko Development can provide no assurance that such expectations will prove to be correct. Forward-looking information and statements contained in this news release are as of the date of this news release and Osisko Development assumes no obligation to update or revise this forward-looking information and statements except as required by law.

Neither the TSXVenture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibilityfor the adequacy or accuracy of this news release. No stock exchange, securities commission or other regulatory authority has approvedor disapproved the information contained herein.