HIGHLIGHTS

• 6,463 m in 14 drill holes of new surface exploration drilling at the Proserpine regional exploration target, located 7 km along strike to the southeast of the Cariboo Gold deposit
• Results confirm the presence of an emerging gold mineralized system comprising high-grade structures exhibiting similarities to those at the Cariboo Gold deposit that, together with broader zones of lower-grade mineralization, may indicate potential for open pit mining methods
• Highlight intercepts include: 95.93 g/t Au over 4.60 m at 71 m vertical depth (including 873.00 g/t Au over 0.50 m), 5.46 g/t Au over 8.60 m at 77 m vertical depth, and 2.17 g/t Au over 14.45 m at 431 m vertical depth

Drilling of an additional 26,500 m planned metres, initially with three rigs, is now resuming following a seasonal hiatus

Osisko Gold Group Inc. (NYSE: OGG) (TSX-V: OGG) is pleased to announce its first set of new diamond drilling results consisting of fourteen holes from the surface exploration program on the Proserpine regional greenfield target, located within the broader Cariboo Gold Project property boundary and approximately 7 kilometres from the Company’s permitted, 100%-owned Cariboo Gold Project in central British Columbia, Canada.

Chris Lodder, President, stated, “We are encouraged by the initial results from the drill campaign at Proserpine, which highlight the potential for a significant new gold mineralized system of scale located only 7 km from the Cariboo Gold deposit. Drilling has intersected high-grade structures showing similarities to those at Cariboo, but also containing areas with broader lower grade mineralization that may indicate potential for bulk mining methods. To date, drilling has broadly tested an area measuring approximately 1.0 km x 0.5 km within a larger target of 6.0 km x 1.0 km gold-in-soil and rock anomaly. For context, the currently defined Cariboo Gold deposit extends approximately 4.0 km along strike by 0.5 km in width, underscoring the exploration potential that remains to be tested at Proserpine.”

DRILL ASSAY HIGHLIGHTS

This news release contains assays from fourteen (14) diamond drillholes totalling 6,463 meters with depths ranging from 36.0 to 734.3 m (see Table 1 and Figure 3) completed between February and May of 2026. All holes were collared in HQ (63.5 millimetre diameter) and reduced to NQ (47.6 millimetre diameter) where necessary to continue advancing. Estimated true widths of intercepts are provided in Table 1. Select highlights include:

• 95.93 grams per tonne gold over 4.60 m at 71 m vertical depth in PSP-26-004, including:
  • 873.00 g/t Au over 0.50 m, and
  • 3.77 g/t Au over 1.20 m
• 5.46 g/t Au over 8.60 m at 77 m vertical depth in PSP-26-001 (Figure 1), including:
  • 16.05 g/t Au over 1.10 m, and
  • 12.50 g/t Au over 0.87 m, and
  • 10.25 g/t Au over 0.50 m, and
  • 5.97 g/t Au over 0.70 m, and
  • 5.21 g/t Au over 0.80 m, and
  • 3.36 g/t Au over 0.60 m, and
  • 1.50 g/t Au over 0.90 m, and
  • 1.18 g/t Au over 0.90 m
• 2.17 g/t Au over 14.45 m at 431 m vertical depth in PSP-26-001, including:
  • 35.10 g/t Au over 0.65 m, and
  • 8.61 g/t Au over 0.50 m, and
  • 2.21 g/t Au over 0.50 m, and
  • 1.21 g/t Au over 0.50 m
• 1.46 g/t Au over 12.40 m at 295 m vertical depth in PSP-26-003, including:
  • 15.40 g/t Au over 1.00 m, and
  • 2.02 g/t Au over 0.50 m
• 3.17 g/t Au over 5.45 m at 334 m vertical depth in PSP-26-009, including:
  • 19.30 g/t Au over 0.60 m, and
  • 9.52 g/t Au over 0.50 m, and
  • 1.22 g/t Au over 0.50 m
• 1.30 g/t Au over 12.00 m at 27 m vertical depth in PSP-26-011, including:
  • 9.92 g/t Au over 0.70 m, and
  • 6.19 g/t Au over 0.50 m, and
  • 3.63 g/t Au over 0.50 m, and
  • 3.75 g/t Au over 0.50 m, and
  • 1.50 g/t Au over 0.65 m
• 2.93 g/t Au over 5.15 m at 233 m vertical depth in PSP-26-001, including:
  • 15.60 g/t Au over 0.95 m
• 4.30 g/t Au over 3.10 m at 226 m vertical depth in PSP-26-001, including:
  • 18.75 g/t Au over 0.50 m, and
  • 7.54 g/t Au over 0.50 m
• 2.79 g/t Au over 4.00 m at 184 m vertical depth in PSP-26-014, including:
  • 11.55 g/t Au over 0.90 m
• 2.30 g/t Au over 4.50 m at 17 m vertical depth in PSP-26-007, including:
  • 12.25 g/t Au over 0.50 m, and
  • 5.62 g/t Au over 0.50 m, and
  • 1.73 g/t Au over 0.50 m, and
  • 1.09 g/t Au over 0.50 m

Results to date have expanded the footprint of known mineralization at Proserpine to approximately 1.0 km along strike by 0.5 km in width, with mineralization remaining open in all directions. All drill holes that reached their intended target depths encountered mineralization, providing a compelling basis for systematic follow-up drilling. Mineralization was encountered from near surface to vertical depths exceeding 400 metres. In particular, hole PSP-26-001 returned several notable mineralized intercepts beginning at a vertical depth of approximately 55 metres and with the deepest at more than 400 metres from surface.

FIGURE 1: 5.46 g/t Au over 8.6 m in PSP-26-001 at approximately 77 m vertical depth.

Drilling also intersected significant intervals of the prospective siliceous sandstone unit, confirming its presence within the target area and providing additional information to refine the geologic model. Based on preliminary observations to date, the siliceous sandstone is believed to represent a more favourable host for mineralization than the calcareous sandstone (see Figure 3).

Diamond drilling at Proserpine has resumed with three active drill rigs following a brief, planned seasonal hiatus. Additional drill rigs may be mobilized as warranted as the planned drill program continues to expand the mineralized footprint and increase drillhole density at Proserpine Southeast, while initiating first-pass drilling at previously untested targets at Proserpine Northwest.

FIGURE 2: Cariboo Gold regional overview.

FIGURE 3: Plan view of Proserpine diamond drilling with select intercept highlights.

FIGURE 4: Proserpine diamond drilling select intercept highlights in long section.

TABLE 1: Select manual composite and individual sample highlights greater than or equal to 1.0 g/t Au.

TABLE 2: Surface DD collar locations, orientations, and max depths.

ABOUT THE PROSERPINE PROSPECT

The Proserpine Mountain prospect area represents a roughly 4 km long post-mineralization fault-bound prospective strike length identified through detailed surface mapping and surface geochemical sampling approximately 7 km along strike to the southeast of the Company’s permitted, 100%-owned Cariboo Gold Project, located in central British Columbia. Mineralization style and controls observed at Proserpine appear to be similar to those observed in the Cariboo Gold deposit area, with high-grade gold intercepts associated with quartz-pyrite to polymetallic (pyrite+/-galena+/-arsenopyrite) quartz veins. Less than half the strike-length of the Proserpine has been drill tested to date, with the current campaign focused on following up on promising preliminary results from the 2019-2020 drilling campaigns at the central southeast limits of the prospect area (Proserpine Southeast). An aggregate total of 10,497 metres of exploration drilling was completed by the Company at the Proserpine regional prospect between 2018 and 2020, not including new drilling contained herein.

ABOUT THE CARIBOO GOLD PROJECT

The Cariboo Gold Project is a permitted, 100%-owned feasibility-stage project located in the historic Wells-Barkerville mining camp of central British Columbia, Canada. Spanning approximately 186,740 hectares, the Company’s land package includes 443 mineral titles and covers an area that extends approximately 77-kilometres from northwest to southeast. In late 2024, the Project was granted the Mines Act and Environmental Management Act (British Columbia) permits, marking the successful completion of the permitting process for key approvals, solidifying the Project’s shovel-ready status.

The Cariboo Gold Project hosts probable mineral reserves of 2.071 million ounces of contained Au (17,815 kt grading 3.62 g/t Au); measured mineral resources of 8,000 ounces of contained Au (47 kt grading 5.06 g/t Au); indicated mineral resources of 1.604 million ounces of contained Au (17,332 kt grading 2.88 g/t Au); and inferred mineral resources of 1.864 million ounces of contained Au (18,774 kt grading 3.09 g/t Au). Mineral resources are reported exclusive of mineral reserves. Mineral resources that are not mineral reserves do not have demonstrated economic viability. The reader is cautioned that inferred mineral resources have a greater degree of uncertainty than indicated mineral resources and must not be converted to mineral reserves; it is reasonably expected, though not guaranteed, that the majority of inferred mineral resources could be upgraded to indicated mineral resources with continued exploration.

Technical Reports

Scientific and technical information relating to the Cariboo Gold Project and the 2025 feasibility study on the Cariboo Gold Project is supported by the technical report, titled “NI 43-101 Technical Report, Feasibility Study for the Cariboo Gold Project, District of Wells, British Columbia, Canada” dated June 11, 2025 (with an effective date of April 25, 2025).

For readers to fully understand the information in the Cariboo Technical Report, reference should be made to the full text of the Cariboo Technical Report in its entirety, including all assumptions, parameters, qualifications, limitations and methods therein. The Cariboo Technical Report is intended to be read as a whole, and sections should not be read or relied upon out of context. The Cariboo Technical Report was prepared in accordance with National Instrument 43-101 – Standards of Disclosure for Mineral Projects and is available electronically on SEDAR+ (www.sedarplus.ca) and on EDGAR (www.sec.gov) under Osisko Gold’s issuer profile and on the Company’s website at www.osiskogold.ca.

Qualified Persons

The scientific and technical information contained in this news release has been reviewed, verified and approved by Scott Smith, P. Geo., Vice President, Exploration of Osisko Gold, a “qualified person” within the meaning of NI 43-101. Verification includes core photo and three-dimensional review of logged drillhole data and assays consistent with the Company’s standard procedures.

The exploration results disclosed in this news release are based on incomplete data and are preliminary in nature. There are no known drilling, sampling, recovery, or other factors that could materially affect the accuracy or reliability of the data; however, readers are cautioned that additional drilling and sampling may result in materially different results than those presented herein.

Quality Assurance – Quality Control

HQ and NQ diameter drill core is cut (halved) on site at the Cariboo Project subsequent to QAQC checks for logging and sampling errors. Quality control samples are inserted at regular intervals in the sample stream, including blanks and reference materials with all sample shipments to monitor laboratory performance. Samples are bagged, labelled, sealed with numbered security tags, and transported to the laboratory under secure chain of custody procedures.

All drill core samples are submitted to ALS Geochemistry’s analytical facility in North Vancouver, British Columbia for preparation and analysis. The ALS facility is accredited to the ISO/IEC 17025 standard for gold assays, and all analytical methods include quality control materials at set frequencies with established data acceptance criteria. The entire sample is crushed, and 250 grams is pulverized. Analysis for gold is by 50 gram fire assay fusion with atomic absorption (AAS) finish with a lower limit of 0.01 ppm and upper limit of 100 ppm. Samples with gold assays greater than 100 ppm are re-analyzed by fire-assay with gravimetric finish (upper limit 10,000 ppm). Select samples containing visible gold and/or cosalite are flagged during logging for an additional 1,000-gram screen metallic fire assay to ensure accurate quantification of any coarse fraction. All samples are also analyzed using a 48 multi-elemental geochemical package by a 4-acid digestion, followed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS).

ABOUT OSISKO GOLD GROUP INC.

Osisko Gold Group Inc. is a continental North American gold development company focused on past producing mining camps with district-scale potential. The Company’s objective is to become an intermediate gold producer through the development of its flagship, fully permitted, 100%-owned Cariboo Gold Project, located in central British Columbia, Canada. Its project pipeline is complemented by the Tintic Project, located in the historic East Tintic mining district in Utah, U.S.A., a brownfield property with significant exploration potential, extensive historical mining data, and access to established infrastructure. Osisko Gold is focused on developing long-life mining assets in mining-friendly jurisdictions while maintaining a disciplined approach to capital allocation, development risk management, and mineral inventory growth.