Mr. Sean Roosen reports

OSISKO DEVELOPMENT INTERCEPTS 443.64 G/T GOLD OVER 1.19 METERS IN UNDERGROUND SAMPLING AT TRIXIE, TINTIC PROJECT

Osisko Development Corp. has released drilling and underground chip sampling results from new development areas as part of its 2023 exploration program at its 100-per-cent-owned Trixie test mine, within the company's wider Tintic project, located in the historic East Tintic mining district in central Utah, United States.

Underground chip sample assay highlights

Assay highlights include underground chip samples from 79 new development faces at Trixie. Of these, 35 faces had samples with greater than one gram per tonne gold or greater than 50 g/t silver values. The remaining chip samples returned no significant assays. Selected assay highlights include:

• 30.85 g/t Au over 1.52 metres in CH01593 (0.90 troy ounce per short ton Au over five feet);
• 17.93 g/t Au and 128.90 g/t Ag over 1.52 m in CH01594 (0.52 oz/t Au and 3.76 oz/t Ag over five ft);
• 5.07 g/t Au over 7.01 m in CH01604 (0.15 oz/t Au over 23 ft), including:
  • 16.80 g/t Au over 1.52 m in CH01604 (0.49 oz/t Au over five ft).
• 443.64 g/t Au over 1.19 m in CH01632 (12.94 oz/t Au over 3.90 ft);
• 23.25 g/t Au and 25.34 g/t Ag over 1.46 m in CH01634 (0.68 oz/t Au and 0.74 oz/t Ag over 4.80 ft).

Chip sample summary:

• Chip samples were collected in new development areas in the face and walls of exploration crosscuts to explore along all domains of the Trixie deposit on the 625 Level, to the north toward the Trixie fault and to the south toward the Sioux Ajax fault.
• The sampling and drilling results provide support that target areas to the north of Trixie and to the south down plunge of the T2 structure are mineralized and warrant further follow-up exploration drilling and sampling.

Drill assay highlights

This news release includes assays from eight underground diamond drill (DD) holes. Select assay highlights include:

• 8.32 g/t Au and 501 g/t Ag over 1.52 m in hole TRXU-DD-23-055 (0.24 oz/t Au and 14.61 oz/t Ag over five ft);
• 9.43 g/t Au and 239 g/t Ag over 1.22 m in hole TRXU-DD-23-056 (0.28 oz/t Au and 6.97 oz/t Ag over four ft);
• 9.04 g/t Au and 323 g/t Ag over 1.52 m in hole TRXU-DD-23-057 (0.26 oz/t Au and 9.42 oz/t Ag over five ft), including:
  • 12.53 g/t Au and 169 g/t Ag over 0.76 m in hole TRXU-DD-23-057 (0.37 oz/t Au and 4.93 oz/t Ag over 2.50 ft).
• 7.46 g/t Au and 301.52 g/t Ag over 2.77 m in hole TRXU-DD-23-059 (0.22 oz/t Au and 8.79 oz/t Ag over 9.10 ft), including:
  • 14.41 g/t Au and 570 g/t Ag over 0.91 m in hole TRXU-DD-23-059 (0.42 oz/t Au and 16.63 oz/t Ag over three ft).

Drill results summary:

• In 2023, the company completed a total of 6,447 m (21,151 ft) of underground drilling in 73 DD holes at Trixie. To date, assays have been received for 59 DD holes, with assays pending for the remaining holes.
• One diamond drill rig is currently active underground testing a copper-gold porphyry target, Trixie West, below the Trixie deposit.
• Approximately 25 per cent of the drilling to date consists of delineation of domains within the area of the current Trixie mineral resource estimate (as defined herein) and 75 per cent is exploration drilling adjacent to the area of the Trixie MRE, including stepouts down dip, down plunge and along strike testing for mineralized structures.
• The focus of these recent holes was to test for mineralization along one of the priority target areas south on strike from the known T2 domain, toward the Sioux Ajax fault.
• A new mineral resource estimate for the Trixie deposit is expected to be completed once all assay results from the 2023 exploration program have been received and surface and underground mapping data has been integrated.

About Trixie

The Trixie test mine is one of several gold and base metal targets within the larger Tintic project consisting of greater than 17,000 acres of patented mining claims and mineral leases within the historic East Tintic mining district of central Utah, U.S. The T2 and T4 structures at Trixie show multiounce gold grades associated with high-sulphidation epithermal mineralization, structurally controlled and hosted within quartzites. The T2 structure mineralization consists of native Au, and rare Au-Ag-rich telluride minerals with quartz. The T4 is a mineralized stockwork zone located in the hangingwall of the T2 and comprises Au-Ag-rich mineralization in host rock quartzite with quartz-barite-sulphosalt stockwork veining. Mineralization reports consistent multiounce gold grades along the entire strike length.

Information relating to the Tintic project and the current MRE for the Trixie deposit is supported by the technical report titled "NI 43-101 Technical Report, Initial Mineral Resource Estimate for the Trixie Deposit, Tintic Project, Utah, United States of America," dated Jan. 27, 2023 (with an effective date of Jan. 10, 2023), prepared for the company by independent representatives of Micon International Ltd. Reference should be made to the full text of the Tintic technical report, which was prepared in accordance with National Instrument 43-101 -- Standards of Disclosure for Mineral Projects and is available electronically on SEDAR+ and on EDGAR under Osisko Development's issuer profile and on the company's website.

Qualified person

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 NI 43-101.

Face sampling methodology

As most structures at Trixie are steeply dipping to the east or west, current sampling procedures are designed to sample the structure. Chip samples are collected and do not exceed one m (three ft) in length. The face is washed for safety, and for better identification of mineralization, alteration and structures. The hangingwall and footwall of the structures are marked up on the face and back, samples intervals are marked up and follow lithological contacts.

Samples are collected in feet and assays are reported in grams per tonne and troy ounce per short ton gold and silver. Conversions to metric and imperial measurements are rounded to two decimal places.

Quality assurance/quality control

All drill core and exploration samples are dispatched to SGS Canada's laboratory in Burnaby, B.C., for off-site sample preparation and analysis. Samples are assigned a unique sample ID. All geological and sampling information is entered into 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. Sample submission forms accompany the samples, and digital copies are emailed to SGS Canada.

All core sample preparation is completed by SGS Canada, including drying, crushing and pulverizing of samples. Analytical assays include gold by 30-gram fire assay with atomic absorption spectroscopy finish (GO_FAA30V10), and gold overlimits by fire assay with gravimetric finish (GO_FAG30V). Multielement analysis (including silver) is by four-acid digest with inductively coupled plasma atomic emission spectroscopy/mass spectrometry finish (GE_ICM40Q12). 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, 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 oz/short ton and g/t.

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. Interlaboratory check assays using ALS Laboratory as a third arty independent analysis of samples is 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 determination is estimated to be approximately 0.3 m to 2.4 m (one to eight ft) wide for the T2 structure, approximately three m to 25 m (10 to 80 ft) for the T4 mineralized stockwork zone located in the hangingwall of the T2 structure and 1.5 m to three m (five to nine ft) for the 75-85 structure.

About Osisko Development Corp.

Osisko Development is a premier North American gold development company focused on high-quality past-producing properties 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 B.C., Canada, the Tintic project in the historic East Tintic mining district in Utah, U.S., 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 growing mineral resources.

We seek Safe Harbor.