Osisko Development Corp. — Capital/Financing Update 2025

Dec 23, 2025

OSISKO DEVELOPMENT CORP.

UNDERTAKING

TO: Autorité des marchés financiers, as Principal Regulator
British Columbia Securities Commission
Alberta Securities Commission
Financial and Consumer Affairs Authority of Saskatchewan
The Manitoba Securities Commission
Ontario Securities Commission
Financial and Consumer Services Commission, New Brunswick
Nova Scotia Securities Commission
Superintendent of Securities, Prince Edward Island
Superintendent of Securities, Newfoundland and Labrador
Superintendent of Securities, Northwest Territories
Superintendent of Securities, Nunavut
Yukon Superintendent of Securities
(collectively, the "Commissions")

Reference is made to the final short form base shelf prospectus of Osisko Development Corp. (the "Corporation") dated December 23, 2025 (the "Prospectus") in connection with the offering by the Corporation, from time to time, of up to $750,000,000 of common shares, debt securities, subscription receipts, warrants and units of the Corporation in each of the provinces and territories of Canada and to subsection 4.2(a)(x) and (x.1) of National Instrument 44-101 – Short Form Prospectus Distributions.

In connection with the filing of the Prospectus, the undersigned, on behalf of the Corporation, hereby undertakes that the Corporation will file (i) any material contracts, including any supplements or amendments thereto, and (ii) documents affecting the rights of securityholders including but not limited to, any indenture or supplemental indenture pursuant to which Securities (as defined in the Prospectus) are offered under any prospectus supplement, any trust indenture or supplemental trust indenture for any offering of debt securities, any subscription receipt agreement or amendment thereto for any offering of subscription receipts and any warrant indenture or supplemental warrant indenture for any offering of warrants, promptly and in any event no later than seven days after the execution or effective date thereof.

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DATED this 23rd day of December, 2025.

OSISKO DEVELOPMENT CORP.

Per: (signed) "Alexander Dann"
Name: Alexander Dann
Title: Chief Financial Officer & VP Finance