Osisko Development Completes 13,000-Meter Infill Drilling Program at Cariboo Gold Project and Provides Update on Ongoing Lowhee Underground Drilling; Intercepts Include 44.68 g/t Gold Over 1.5 Meters From 27.9 Meters Downhole, Including 133.62 g/t Gold Over 0.5 Meters From 28.4 Meters Downhole

HIGHLIGHTS

• 13,684 m of grid infill drilling accomplished (2,659 m new outcomes) on 10-m drill spacing in 142 drill holes from August 2025 representing everything of the deliberate Appian infill program
• Spotlight intercepts embrace: 44.68 g/t Au over 1.5 m from 27.9 m downhole (together with 133.62 g/t Au over 0.5 m from 28.4 m downhole), and 25.78 g/t Au over 2.5 m from 41.3 m downhole (together with 103.47 g/t Au over 0.5 m from 42.8 m downhole, and 12.51 g/t Au over 1.0 m from 41.8 m downhole)
• 2,995 m of extra infill and close to mine exploration drilling accomplished as a part of ongoing Lowhee zone underground diamond drilling
• Spotlight intercepts embrace: 31.64 g/t Au over 2.0 m from 50.0 m downhole (together with 125.24 g/t over 0.5 m from 50.5 m downhole), and 11.21 g/t Au over 4.9 m from 63.3 m downhole (together with 58.19 g/t Au over 0.7 m from 65.0 m downhole, and 17.57 g/t Au over 0.7 m from 63.3 m downhole).
• Outcomes up to now proceed to contribute to a extra detailed understanding of spatial controls and native variability inside Lowhee Zone and give constructive indications for close to mine potential

MONTREAL, June 09, 2026 (GLOBE NEWSWIRE) — Osisko Development Corp. (NYSE: ODV, TSXV: ODV) (“Osisko Development” or the “Firm“) is happy to announce new infill drilling outcomes from its accomplished 13,000-meter program on 10 meter drill spacing, in addition to new outcomes from extra infill and close to mine exploration actions within the Lowhee Zone of the Firm’s permitted, 100%-owned Cariboo Gold Project (the “Project“), situated in central British Columbia (“B.C.“), Canada. Three of the six drill gap followers reported herein comprise the ultimate 2,659 meters (“m“) of the 13,000 m underground infill program, bringing the ultimate tally of drilling with full outcomes to 13,684 m. The remaining three followers comprise an extra 2,995 m of infill and close to mine exploration drilling at the L1290-ORE-000 and L1260-ORE-002 ranges. Reconciliation work is underway on an up to date localized block mannequin, with last outcomes anticipated within the second quarter of 2026.

Chris Lodder, President, said, “The completion of the tighter infill drill spacing provides us a greater understanding of vein hall spatial geometries and native variability particular to this a part of the Lowhee deposit, and provides us confidence going ahead to assist refine infill drill necessities, manufacturing designs and sequencing within the Lowhee deposit of the Cariboo Gold Project. The extra infill and close to mine exploration intercepts reinforce the significance of continued drilling in underexplored zones.”

DRILL ASSAY HIGHLIGHTS

This information launch contains assays from fifty-five (55) underground infill and close to mine exploration HQ diamond drill (“DD“) holes (63.5-millimeter diameter) totaling 5,654 m with depths starting from 76.5 to 138 m (see Desk 1 and Determine 2). Choose photon and hearth assay highlights embrace:

• 44.68 grams per tonne (“g/t”) gold (“Au”) over 1.5 m in BMU-25-176 from 27.9 downhole, together with:
  • 133.62 g/t Au over 0.5 m from 28.4 m downhole
• 25.78 g/t Au over 2.5 m in BMU-26-055 from 41.3 m downhole, together with:
  • 103.47 g/t Au over 0.5 m from 42.8 downhole, and
  • 12.51 g/t Au over 1.0 m from 41.8 downhole

• 31.64 g/t Au over 2 m in BMU-26-034 from 50.0 m downhole, together with:
  • 125.24 g/t Au over 0.5 m from 50.5 m downhole, and
• 11.21 g/t Au over 4.9 m in BMU-26-031 from 63.3 m downhole, together with:
  • 58.19 g/t Au over 0.7 m from 65.0 m downhole, and
  • 17.57 g/t Au over 0.7 m from 63.3 m downhole

• 21.84 g/t Au over 2.5 m in BMU-26-008 from 79.7 m downhole, together with:
  • 91.3 g/t Au over 0.5 m from 79.7 m downhole, and
  • 6.79 g/t Au over 0.5 m from 81.2 m downhole, and
  • 5.97 g/t Au over 0.5 m from 80.7 m downhole, and
  • 2.66 g/t Au over 0.5 m from 80.2 m downhole, and
  • 2.47 g/t Au over 0.5 m from 81.7 m downhole
• 91.99 g/t Au over 0.5 m in BMU-26-013 from 73.75 m downhole
• 18.59 g/t Au over 2.65 m in BMU-26-006 from 43.35 m downhole, together with:
  • 48.93 g/t Au over 1.0 m from 43.85 m downhole
• 4.76 g/t Au over 6.05 m in BMU-26-037 from 85.0 m downhole, together with:
  • 44.79 g/t Au over 0.5 m from 88.5 m downhole, and
  • 6.13 g/t Au over 0.5 m from 88.0 m downhole, and
  • 4.02 g/t Au over 0.5 m from 87.0 m downhole
• 3.28 g/t Au over 7.3 m in BMU-25-179 from 81.7 m downhole, together with:
  • 12.73 g/t Au over 0.95 m from 84.85 m downhole, and
  • 9.68 g/t Au over 0.9 m from 85.8 m downhole
• 46.37 g/t Au over 0.5 m in BMU-26-022 from 14.0 m downhole

Full assay highlights, together with true width estimates, are introduced in Desk 1 and drill gap places and orientations are listed in Desk 2. Intervals not recovered had been assigned zero grade. Prime cuts haven’t been utilized to excessive grade assays.

DISCUSSION OF RESULTS

• Figures 4-6 (1260 degree): Reduce-off assay composites finishing the deliberate 13,000 m systematic grid infill program. These final three followers had been testing areas peripheral to order stopes, and exterior the modeled vein corridors. Intercepts acquired up to now counsel attainable extensions of vein corridors, with potential for useful resource conversion and upside mineralization.
• Figures 7-8 (1290 Stage): Reduce-off assay composites from extra infill drilling at the 1290 ranges present a level of spatial correlation with the modelled reserve stopes with intercepts exterior these areas suggesting potential for useful resource conversion and upside mineralization.
• Determine 9 (1260 Stage): Reduce-off assay composites from infill and close to mine exploration drilling to the southeast at the 1260 degree embrace a number of new intercepts exterior the present vein corridors and useful resource footprint.
• All intercepts might be included within the deliberate remodelling and mineral useful resource calculation course of to find out their implications on an up to date native block mannequin and any potential changes to deliberate reserve stopes. In sure areas, this may occasionally assist the addition of latest deliberate reserve stopes, topic to the ultimate estimation course of final result.

Determine 1: Cariboo Gold Project deposit map with Location of Lowhee Zone and Cow Portal underground entry.

Determine 2: Location and overview of ongoing Lowhee Zone underground definition infill and close to mine exploration diamond drilling

Determine 3: Lowhee Zone choose underground drilling highlights (plan view).

Determine 4: L1260-ORE-003 Lowhee Zone grid infill choose underground drill assay highlights (this launch) with beforehand launched floor and underground diamond drilling ends in cross part by fan. Outcomes from instantly adjoining followers inside slice omitted for visible readability (20 m slice trying 048°).

Determine 5: L1260-ORE-003 Lowhee Zone grid infill choose underground drill assay highlights (this launch) with beforehand launched floor and underground diamond drilling ends in cross part by fan. Outcomes from instantly adjoining followers inside slice omitted for visible readability (20 m slice trying 060°).

Determine 6: L1260-ORE-003 Lowhee Zone grid infill choose underground drill assay highlights (this launch) with beforehand launched floor and underground diamond drilling ends in cross part by fan. Outcomes from instantly adjoining followers inside slice omitted for visible readability (20 m slice trying 073°).

Determine 7: L1290-ORE-000 Lowhee Zone infill choose underground drill assay highlights (this launch) with beforehand launched floor and underground diamond drilling ends in cross part by fan. Outcomes from instantly adjoining followers inside slice omitted for visible readability (20 m slice trying 017°).

Determine 8: L1290-ORE-000 Lowhee Zone infill choose underground drill assay highlights (this launch) with beforehand launched floor and underground diamond drilling ends in cross part by fan. Outcomes from instantly adjoining followers inside slice omitted for visible readability (20 m slice trying 025°).

Determine 9: L1260-ORE-002 Lowhee Zone infill and close to mine exploration choose underground drill assay highlights (this launch) with beforehand launched floor and underground diamond drilling ends in cross part by fan. Outcomes from instantly adjoining followers inside slice omitted for visible readability (20 m slice trying 051°).

Desk 1: Size weighted assay composites and particular person samples>=1.8 g/t for Lowhee Zone underground DD.

Desk 2: Underground DD collar places, drillhole orientations, and max depths. Adverse dips level down.

ABOUT LOWHEE ZONE

Geological mapping and geochemical sampling had been carried out on Barkerville Mountain from 2017-2018, with the Lowhee Zone recognized as a high-priority drill goal. From 2019 to 2022, a complete of 167 floor drill holes had been accomplished, totaling 54,494.5 m.

Lowhee zone entry is thru Cow portal on the northwestern flank of Barkerville Mountain (Determine 1 and Determine 2) Cow portal development was accomplished in This autumn 2024 and improvement of the underground ramp into the Lowhee zone commenced in Q1 2025. The possible mineral reserves estimate for the Lowhee Zone contains 104,491 ounces of contained Au (923,162 tonnes grading 3.52 g/t Au) and represents roughly 5% of the overall contained gold within the estimated possible mineral reserves for the Cariboo Gold Project.

ABOUT CARIBOO GOLD PROJECT

The Cariboo Gold Project is a permitted, 100%-owned feasibility-stage challenge situated within the historic Wells-Barkerville mining camp of central British Columbia, Canada. Spanning roughly 186,740 hectares, the Firm’s land package deal contains 443 mineral titles and covers a ~83-kilometre strike of extremely potential exploration targets extending northwest to southeast. In late 2024, the Project was granted the Mines Act and Environmental Administration Act (British Columbia) permits, marking the profitable completion of the allowing course of for key approvals, solidifying the Project’s shovel-ready standing.

The Cariboo Gold Project hosts possible mineral reserves of two.071 million ounces of contained Au (17,815 kt grading 3.62 g/t Au); measured mineral sources of 8,000 ounces of contained Au (47 kt grading 5.06 g/t Au); indicated mineral sources of 1.604 million ounces of contained Au (17,332 kt grading 2.88 g/t Au); and inferred mineral sources of 1.864 million ounces of contained Au (18,774 kt grading 3.09 g/t Au). Mineral sources are reported unique of mineral reserves.

Technical Experiences

Scientific and technical data regarding the Cariboo Gold Project and the 2025 feasibility examine on the Cariboo Gold Project is supported by the technical report, titled “NI 43-101 Technical Report, Feasibility Examine for the Cariboo Gold Project, District of Wells, British Columbia, Canada” and dated June 11, 2025 (with an efficient date of April 25, 2025) (the “Cariboo Technical Report“).

For readers to completely perceive the data within the Cariboo Technical Report, reference must be made to the total textual content of the Cariboo Technical Report in its entirety, together with all assumptions, parameters, {qualifications}, limitations and strategies therein. The Cariboo Technical Report is meant to be learn as a complete, and sections shouldn’t be learn or relied upon out of context. The Cariboo Technical Report was ready in accordance with Nationwide Instrument 43-101 – Requirements of Disclosure for Mineral Tasks (“NI 43-101“) and is offered electronically on SEDAR+ (www.sedarplus.ca) and on EDGAR (www.sec.gov) beneath Osisko Development’s issuer profile and on the Firm’s web site at www.osiskodev.com.

Certified Individuals

The scientific and technical data contained on this information launch has been reviewed, verified and accepted by Scott Smith, P. Geo., Vice President, Exploration of Osisko Development, a “certified individual” inside the which means of NI 43-101. Verification contains core photograph and three-dimensional evaluate of logged drillhole information and assays according to the Firm’s normal working procedures.

High quality Assurance (QA) – High quality Management (QC)

Complete core sampling was used for all definition infill HQ core accomplished within the logging amenities following day by day QAQC checks for logging and sampling errors. High quality management (QC) samples are inserted at common intervals within the pattern stream, together with blanks and reference supplies with all pattern shipments to watch laboratory efficiency. Samples are bagged, labeled, sealed with numbered safety tags.

Samples are taken by expeditor from the logging amenities direct to MSALABS’s analytical facility in Prince George, B.C., Canada, for preparation and evaluation. The MSALABS facility is accredited to the ISO/IEC 17025 normal for gold assays and all analytical strategies embrace high quality management supplies at set frequencies with established information acceptance standards. Your complete pattern is dried, crushed, and break up into sealed containers. Evaluation for gold is by gamma ray evaluation utilizing the Chrysos PhotonAssay (PA1408X). Samples are bombarded with gamma rays and the ensuing sign is shipped to the detectors.

Close to mine exploration infill HQ drill core samples are lower on website and submitted to ALS Geochemistry’s analytical facility in North Vancouver, British Columbia for preparation and evaluation. The ALS facility is accredited to the ISO/IEC 17025 normal for gold assays and all analytical strategies embrace high quality management supplies at set frequencies with established information acceptance standards. Your complete pattern is crushed, and 250 grams is pulverized. Evaluation for gold is by 50 gram hearth assay fusion with atomic absorption (AAS) end with a decrease restrict of 0.01 ppm and higher restrict of 100 ppm. Samples with gold assays better than 100 ppm are re-analyzed utilizing a 1,000-gram display metallic hearth assay. A specific variety of samples are additionally analyzed utilizing a 48 multi-elemental geochemical package deal by a 4-acid digestion, adopted by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS).

ABOUT OSISKO DEVELOPMENT CORP.

Osisko Development Corp. is a continental North American gold improvement firm targeted on previous producing mining camps with district scale potential. The Firm’s goal is to develop into an intermediate gold producer via the event of its flagship, totally permitted, 100%-owned Cariboo Gold Project, situated in central British Columbia, Canada. Its challenge pipeline is complemented by the Tintic Project situated within the historic East Tintic mining district in Utah, U.S.A., a brownfield property with important exploration potential, in depth historic mining information, and entry to established infrastructure. Osisko Development is concentrated on creating long-life mining property in mining-friendly jurisdictions whereas sustaining a disciplined method to capital allocation, improvement threat administration, and mineral stock progress.

For additional data, go to our web site at www.osiskodev.com or contact:

CAUTION REGARDING FORWARD LOOKING STATEMENTS

This information launch comprises “forward-looking data” (inside the which means of relevant Canadian securities legal guidelines) and “forward-looking statements” (inside the which means of the U.S. Non-public Securities Litigation Reform Act of 1995, as amended) (collectively, “forward-looking statements”). Such forward-looking statements are recognized with phrases resembling “might”, “will”, “would”, “might”, “anticipate”, “consider”, “count on”, “plan”, “intend”, “potential”, “estimate”, “suggest”, “challenge”, “outlook”, “foresee”, “goal”, “technique”, variants of those phrases or the unfavourable or comparable terminology, in addition to phrases normally used sooner or later and the conditional. Data contained in forward-looking statements relies upon sure materials assumptions that had been utilized in drawing a conclusion or making a forecast or projection, together with the assumptions, {qualifications}, limitations or statements pertaining to: the utility and significance of outcomes to contribute to a extra detailed understanding of spatial controls and native variability inside the Lowhee Zone and its capacity and significance in offering constructive indication (if any) for close to mine potential; the outcomes, timing, utility and significance of the infill drill program and its impacts on the localized block mannequin and/or future manufacturing stope designs and sequencing (if any); the tighter infill drilling spacing offering higher understanding of vein hall spatial geometries and native variability inside Lowhee; the flexibility of outcomes (if any) to assist refine infill drill necessities, manufacturing designs and sequencing within the Lowhee deposit; the importance of continued drilling in underexplored zones; the interpretation and accuracy of intercepts to counsel attainable extensions of vein corridors, with potential for useful resource conversion and upside mineralization; the interpretation and accuracy of assay composites displaying a level of spatial correlation with the modelled reserve stopes with intercepts exterior these areas suggesting potential for useful resource conversion and upside mineralization; the prospectivity of exploration within the Lowhee Zone and targets exterior of at present outlined mineral reserves and/or mineral sources; the consistency of outcomes with modelled reserve stopes (if at all); the interpretation and accuracy of spatial geometries, geological construction and native variability modeling and assumptions in regard to potential reserve or useful resource revisions (if at all); the flexibility and timing (if at all) to finish deliberate remodelling and mineral useful resource calculation course of; the importance of implications (if any) on an up to date native block mannequin and any potential changes to deliberate reserve stopes; the flexibility of estimation outcomes (if any) to assist the addition of latest deliberate reserve stopes; the outcomes (if any) of additional exploration work and capacity of the Firm to outline and develop mineral sources past present mineral useful resource estimates; the flexibility and utility of exploration work (together with drilling) to tell useful resource modeling, mine planning, manufacturing stope design procedures and parameters, refinement of infill drill necessities, and the suitable drill spacing for future infill drilling (if at all); assumptions, {qualifications} and parameters underlying the Cariboo Technical Report (together with, however not restricted to, the mineral sources, mineral reserves, manufacturing profile, mine design and challenge economics); the outcomes of the Cariboo Technical Report as an indicator of high quality and robustness of the Cariboo Gold Project, in addition to different issues which might be believed to be applicable within the circumstances; the flexibility of the Firm to realize the estimates outlined within the Cariboo Technical Report within the timing contemplated (if at all); mineral useful resource class conversion; the longer term improvement and operations at the Cariboo Gold Project; administration’s perceptions of historic tendencies, present circumstances and anticipated future developments; the utility and significance of historic information, together with the importance of the district internet hosting previous producing mines; the flexibility of exploration work (together with drilling and sampling) to precisely predict mineralization; the flexibility of the Firm to finish its exploration and improvement aims for its tasks within the timing contemplated and inside anticipated prices (if at all); the flexibility to adapt to modifications in gold costs, estimates of prices, estimates of deliberate exploration and improvement expenditures; the Firm’s technique and aims regarding the Cariboo Gold Project in addition to its different tasks; the assumptions, {qualifications} and limitations regarding the Cariboo Gold Project being permitted; the exploration potential and prospectivity (if any) of its properties; regulatory framework remaining outlined and understood in addition to different issues which might be believed to be applicable within the circumstances, and another data herein that’s not a historic reality could also be “ahead trying data”. Precise outcomes might differ materially because of numerous elements, together with, with out limitation: dangers regarding third-party approvals, together with the issuance of permits by governments, capital market circumstances and the Firm’s capacity to entry capital on phrases acceptable to the Firm for the contemplated exploration and improvement at the Firm’s properties; dangers associated to the exploration, improvement and operation of the Cariboo Gold Project; dangers associated to geological modeling and useful resource estimation; well being, security and safety incidents; regulatory delays or modifications in regulatory framework and relevant legal guidelines; labour shortages or disputes; basic financial and market circumstances and enterprise circumstances within the mining trade; fluctuations in commodity and foreign money trade charges; modifications in regulatory framework and relevant legal guidelines, in addition to these dangers and elements disclosed within the Firm’s most up-to-date annual data type, monetary statements and administration’s dialogue and evaluation in addition to different public filings on SEDAR+ (www.sedarplus.ca) and on EDGAR (www.sec.gov). Though the Firm believes the expectations conveyed by the forward-looking statements are affordable primarily based on data obtainable as of the date hereof, no assurances might be given as to future outcomes, ranges of exercise and achievements. The Firm disclaims any obligation to replace any forward-looking statements, whether or not because of new data, future occasions or outcomes or in any other case, besides as required by legislation. Ahead-looking statements will not be ensures of efficiency and there might be no assurance that these forward-looking statements will show to be correct, as precise outcomes and future occasions might differ materially from these anticipated in such statements. Accordingly, readers shouldn’t place undue reliance on forward-looking statements.

Neither the TSX Enterprise Change nor its Regulation Providers Supplier (as that time period is outlined within the insurance policies of the TSX Enterprise Change) accepts duty for the adequacy or accuracy of this information launch. No inventory trade, securities fee or different regulatory authority has accepted or disapproved the data contained herein.

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