Mr. Sean Roosen reports

OSISKO DEVELOPMENT FILES TECHNICAL REPORT ON MINERAL RESOURCE ESTIMATE FOR THE TRIXIE DEPOSIT, TINTIC PROJECT

Osisko Development Corp. has filed a technical report for the updated mineral resource estimate on its 100-per-cent-owned underground Trixie deposit within the company's wider Tintic project, located in the historic East Tintic mining district in central Utah, United States. Highlights from the previously announced 2024 Trixie MRE disclosed in the company's news release dated March 15, 2024, are presented herein, and are consistent with the technical report.

The technical report, titled "NI 43-101 Technical Report, Mineral Resource Estimate for the Trixie Deposit, Tintic Project, Utah, United States of America," and dated April 25, 2024 (with an effective date of March 14, 2024), was prepared for the company by independent representatives of Micon International Ltd. in accordance with National Instrument 43-101 (Standards of Disclosure for Mineral Projects). Reference should be made to the full text of the technical report, which is available electronically on SEDAR+ and on EDGAR under Osisko Development's issuer profile and on the company's website.

Qualified persons

The scientific and technical information contained in this news release has been reviewed and approved by Maggie Layman, PGeo, vice-president, exploration, of Osisko Development, and a qualified person within the meaning of National Instrument 43-101.

The independent QPs for the 2024 Trixie MRE, within the meaning of NI 43-101, are William Lewis, PGeo, and Alan J. San Martin, MAusIMM (CP), of Micon International. Each QP is independent of Osisko Development within the meaning of NI 43-101, and has reviewed and approved the content in this news release.

Quality assurance/quality control

All drill core and exploration samples are dispatched to ALS Geochemistry or SGS Canada for off-site sample preparation and analysis. Both labs are ISO/IEC 17025 certified, and ALS Geochemistry is also ISO 9001 certified. Samples are assigned a unique sample ID. All geological and sampling information is entered into a Datamine Fusion database. Core is sawn in half, and half is sampled. Certified standards and blanks are inserted into all sample dispatches. Samples are collected by Old Dominion Transportation and dispatched to SGS Canada's laboratory in Burnaby, B.C., or ALS Geochemistry's laboratories in Elko, Nev., or Twin Falls, Idaho. Sample submission forms accompany the samples, and digital copies are e-mailed to the destination lab.

Core sample preparation is completed by ALS Geochemistry or SGS Canada, including drying, crushing and pulverizing of samples. Analytical assays include gold by 30-gram fire assay with AAS finish, and gold overlimits by fire assay with gravimetric finish. Screen metallic analyses are performed on selected samples. Multielement analysis (including silver) is by four-acid digest with ICP-AES/ICP-MS finish. The pulps are returned to Osisko Development, and coarse rejects are disposed after 90 days. Assays are reported to Osisko Development and then loaded into Datamine Fusion. Quality assurance/quality control samples are checked, and assays are merged with sample information for future reporting.

Underground face samples are collected by company geologists from each of the active mining faces, with samples transported by the geologists from Trixie to the on-site company laboratory located at the Burgin administrative complex. Underground samples are dried and crushed to less than 10 millimetres, and a 250-gram split is taken. The split is pulverized, and a 30-gram fire assay with gravimetric finish is completed to determine gold and silver grades, reported in ounces per short ton and grams per tonne.

The company's Burgin laboratory is not a certified analytical laboratory, but the facility is managed by a qualified laboratory manager with annual auditing by technical staff. The laboratory has been independently audited by Qualitica Consulting and Micon International's QP with recommendations implemented. Interlaboratory check assays using ALS Geochemistry as a third party independent analysis of samples are routinely carried out as part of continuing QA/QC work. Certified OREAS QC standards and blanks are inserted at regular intervals in the sample stream to monitor laboratory performance.

True width is estimated to be approximately 0.5 metre to three metres (1.6 feet to 10 feet) for all fissure veins and discrete structures (T2, T3, 75-85, Wildcat and 40 fault), and the T4 zone is modelled at an average width of 90 m (300 ft), and encompasses disseminated mineralization and discontinuous veins ranging from several centimetre to one m (three ft).

About Osisko Development Corp.

Osisko Development is a North American gold development company focused on past-producing mining camps located in mining-friendly jurisdictions with district-scale potential. The company's objective is to become an intermediate gold producer by advancing its 100-per-cent-owned Cariboo gold project, located in central British Columbia, Canada, the Tintic project in the historic East Tintic mining district in Utah, United States, and the San Antonio gold project in Sonora, Mexico. In addition to considerable brownfield exploration potential of these properties that benefit from significant historical mining data, existing infrastructure and access to skilled labour, the company's project pipeline is complemented by other prospective exploration properties. The company's strategy is to develop attractive, long-life, socially and environmentally sustainable mining assets, while minimizing exposure to development risk and increasing mineral resources.

We seek Safe Harbor.