OGG.V · 2025-12-15

Osisko Development Provides Infill Drilling Update on Its 13,000-m Program at Cariboo Gold Project; Intercepts Include 8.56 g/t Au over 8.5m from 60.5m Depth, and 130.32 g/t Au over 0.5m from 83.5m Depth

Drill Results Resource Estimates Exploration Programs

ODV NYSE TSXV News Release

OSISKO DEVELOPMENT PROVIDES INFILL DRILLING UPDATE ON ITS 13,000-m PROGRAM AT CARIBOO GOLD PROJECT; INTERCEPTS INCLUDE 8.56 g/t AU OVER 8.5m FROM 60.5m DEPTH, AND 130.32 g/t AU OVER 0.5m FROM 83.5m DEPTH

HIGHLIGHTS

 5,983 m of infill drilling completed (3,704 m of new results) on 10-m drill spacing in 62 drill holes

from August 2025, representing ~44% of the total planned 13,000-m infill program

 Highlights include: 8.56 g/t Au over 8.5m from 60.5m depth, 16.95 g/t Au over 4.0m from 80m depth (including 130.32 g/t Au over 0.5m from 83.5m depth), and 9.32 g/t Au over 6.0m from 58m depth

 Results to date continue to be broadly consistent with modelled reserve stopes, indicate potential

for upside mineralization in new areas, and provide key spatial controls that will inform an updated local block model and refine future production stope designs

 An aggregate total of 10,000 m (~72%) of total planned drill meters have been completed to

date, with full assays and QA/QC pending for the remaining holes not reported

 Infill program on track to wrap up in Q1 2026

Montreal, Québec, December 15, 2025 – Osisko Development Corp. (NYSE: ODV, TSXV: ODV) ("Osisko Development" or the "Company") is pleased to announce new infill drilling results from its ongoing 13,000-meter program on 10 meter drill spacing that commenced in August 2025 in the Lowhee Zone of the Company's permitted, 100%-owned Cariboo Gold Project ("Cariboo" or the "Project"), located in central British Columbia ("B.C."), Canada. The six drill hole fans reported herein comprise an additional ~3,704 meters ("m") of underground infill drilling, bringing the total tally of drilling with full results to 5,983 m, or ~44% of the planned total.

In total, an aggregate of approximately 10,000 meters, representing ~72% of the total planned drill meters, has now been completed. Full assay results and associated quality assurance and quality control reviews are pending for the remaining holes not reported herein.

Chris Lodder, President, stated, "We continue to see good alignment of ongoing infill drilling results with our modelled vein corridors and planned stope shapes, along with occurrences of upside mineralized zones outside current reserve outlines. This tighter drill spacing sharpens our understanding of vein corridor spatial geometries and local variability, while reinforcing the importance of infill drilling in underexplored zones. As this work concludes in the first quarter of 2026, the resulting information is expected to help refine production designs and sequencing."

DRILL ASSAY HIGHLIGHTS

This news release includes assays from thirty-eight (38) underground infill HQ diamond drill ("DD") holes (63.5-millimeter diameter) totaling ~3,704 m with depths ranging from 81 to 114 m completed between September 2025 and early November 2025 (see Table 1). Assays for five (5) complete drill fans were received by November 27, 2025 (Figure 2). Select photon assay highlights include:

8.56 grams per tonne ("g/t") gold ("Au") over 8.5 m from 60.5 m depth in hole BMU-

25-090, including:

64.26 g/t over 0.5 m from 63.5 m depth, and
43.80 g/t over 0.5 m from 62.5 m depth, and
12.86 g/t over 0.5 m from 62 m depth, and
10.71 g/t over 0.5 m from 61 m depth, and
3.35 g/t over 0.5 m from 66.5 m depth, and

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2.69 g/t over 0.5 m from 63 m depth, and
2.67 g/t over 0.5 m from 64 m depth
16.95 g/t over 4.0 m from 80 m depth in BMU-25-104, including:
130.32 g/t over 0.5 m from 83.5 m depth, and
4.37 g/t over 0.5 m from 80 m depth
9.32 g/t over 6.0 m from 58 m depth in BMU-25-092, including:
51.09 g/t over 0.5 m from 63 m depth, and
26.51 g/t over 0.5 m from 62 m depth, and
23.52 g/t over 0.5 m from 59.7 m depth, and
3.10 g/t over 0.7 m from 60.2 m depth, and
3.21 g/t over 0.5 m from 60.9 m depth
13.22 g/t over 2.65 m from 87.85 m depth in BMU-25-108, including:
65.63 g/t over 0.5 m from 90 m depth, and
3.97 g/t over 0.5 m from 87.85 m depth
26.14 g/t over 2.0 m from 2.5 m depth in BMU-25-110, including:
103.94 g/t over 0.5 m from 3 m depth
11.12 g/t over 4.5 m from 70.5 m depth in BMU-25-084, including:
88.87 g/t over 0.5 m from 71.5 m depth, and 7.08 g/t over 0.5 m from 72 m depth, and

4.76 g/t over 0.5 m from 76.5 m depth
11.23 g/t over 3.9 m from 59.1 m depth in BMU-25-087, including:
43.0 g/t over 1.0 m from 60.8 m depth
7.32 g/t over 4.0 m from 15 m depth in BMU-25-101, including:
57.72 g/t over 0.5 m from 16.5 m depth, and
1.87 g/t over 0.5 m from 17.5 m depth
31.32 g/t over 1.0 m from 42.9 m depth in BMU-25-104, including:
62.15 g/t over 0.5 m from 42.9 m depth
6.48 g/t over 4.55 m from 50.45 m depth in BMU-25-108, including:
21.04 g/t over 0.5 m from 51.45 m depth, and
12.18 g/t over 0.5 m from 51.95 m depth, and
8.71 g/t over 0.55 m from 53.45 m depth, and
7.0 g/t over 0.5 m from 54 m depth, and
4.41 g/t over 0.5 m from 50.95 m depth, and
2.88 g/t over 0.5 m from 52.95 m depth

Complete assay highlights, including true width estimates, are presented in Table 1 and drill hole locations and orientations are listed in Table 2. Intervals not recovered by drilling were assigned zero grade. Top cuts have not been applied to high grade assays.

DISCUSSION OF RESULTS

Based on the results observed to date, there is a positive correlation between the above cut-off assay composites and the modelled reserve stopes. Individual intercepts are not expected to align precisely with the modelled areas, and a degree of variability within the vein corridors is both anticipated and acceptable as tighter spaced infill drilling informs a refinement of the local reserve model. This work is one of the key objectives of the ongoing program.

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Occurrences of above cut-off assay are also being observed in areas not previously included in the reserve model, suggesting potential for upside mineralization. These intervals will be incorporated in the planned remodelling and mineral resource calculation process to determine their implications on the updated local block model and any potential adjustments to planned reserve stopes. In certain areas, this may support the addition of new planned reserve stopes, subject to the final estimation process outcome.
A spatial offset of certain intercepts when compared to the modelled vein corridors and mineral reserve stope shapes is evident in the cross sections. This reflects, in part, the lower spatial accuracy of the surface-based drill hole data compared to underground drilling, which carries higher survey precision, as well as the more oblique angles of intercepts that the surface-based drill holes have with the vein planes. These factors will be accounted for in the vein corridor remodelling process to be undertaken upon conclusion of this program, and will serve as an important operational template for future infill drilling used in production stope design.

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

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Figure 2: Location and overview of the ongoing 13,000-meter infill drilling campaign.

Figure 3: Lowhee Zone infill select underground drilling highlights (plan view).

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Figure 4: Lowhee Zone infill select underground drill assay highlights (this release) with previously released surface and underground diamond drilling results in cross section by fan.

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Table 1: Length weighted assay composites and individual samples>=1.8 g/t for Lowhee Zone underground DD.

	Drillhole ID	From (m)	To (m)	Length (m)	Au (g/t)	Est. True Width (m)
BMU-25-084 12.25 16.25 4 2.28 2.83 Including 13.25 13.75 0.5 16.62 28.5 29 0.5 2.20 0.36 32 32.5 0.5 2.23 0.41 33 33.5 0.5 2.80 0.43 36.5 37.5 1 13.52 0.71 Including 36.5 37 0.5 26.84 64 64.5 0.5 2.27 0.35 67 68 1 1.92 0.82 70.5 75 4.5 11.12 4.08 Including 71.5 72 0.5 88.87 0.45 and 72 72.5 0.5 7.08 76.5 77 0.5 4.76 0.32
BMU-25-086 0.4 0.9 0.5 5.40 0.49 64 65.6 1.6 3.11 1.18 Including 65 65.6 0.6 5.63 67.5 68 0.5 3.44 0.45 77.8 78.3 0.5 4.79 0.37 101.5 104 2.5 2.03 1.77 Including 103 103.5 0.5 5.71 and 103.5 104 0.5 2.40
BMU-25-087 18 18.5 0.5 3.76 0.41 19.6 23 3.4 2.26 2.79 Including 20.6 21.1 0.5 14.50 57.5 58.1 0.6 2.68 0.34 59.1 63 3.9 11.23 2.76 Including 60.8 61.8 1 43.00 0.82 73.3 79.3 6 4.56 5.25 Including 74.8 75.3 0.5 6.90 0.32 and 77.3 77.8 0.5 28.19 0.50 and 77.8 78.3 0.5 15.00 0.40 92.3 92.8 0.5 3.76 0.40 105.9 106.4 0.5 3.72 0.41
BMU-25-088 12 16 4 3.60 3.76 Including 12 12.5 0.5 12.85 0.43 and 12.5 13 0.5 13.14 0.49 51 52 1 2.34 0.91 Including 51 51.5 0.5 2.40 0.45 and 51.5 52 0.5 2.27 0.45 54 57.5 3.5 2.84 3.17 Including 57 57.5 0.5 17.00 59.5 60 0.5 1.86 0.43 95.6 96.1 0.5 4.58 0.49
BMU-25-089 45.5 46 0.5 2.56 0.43 59.3 60.7 1.4 5.64 1.25 Including 60.2 60.7 0.5 15.58 0.43 100 100.5 0.5 4.20 0.49
BMU-25-090 6 7 1 13.34 0.71 16.3 18 1.7 1.98 1.54 Including 17 18 1 3.13 50.9 51.9 1 3.09 0.79 Including 51.4 51.9 0.5 5.98 60.5 69 8.5 8.56 7.51 Including 61 61.5 0.5 10.71 0.41 and 62 62.5 0.5 12.86 and 62.5 63 0.5 43.80 0.45 and 63 63.5 0.5 2.69 0.45 and 63.5 64 0.5 64.26 0.43 and 64 64.5 0.5 2.67 and 66.5 67 0.5 3.35 0.45 73 73.5 0.5 2.38 0.38 87.25 87.75 0.5 2.29 0.41 97.35 97.85 0.5 8.30 0.41 101.5 102 0.5 2.74 0.45
BMU-25-091 10.15 11.15 1 1.93 0.50

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	Drillhole ID	From (m)	To (m)	Length (m)	Au (g/t)	Est. True Width (m)
Including 10.15 10.65 0.5 2.76 19.5 20 0.5 2.18 0.49 22 23 1 3.85 0.97 Including 22.5 23 0.5 7.29 42.5 46 3.5 4.93 3.17 Including 42.5 43 0.5 2.53 0.43 and 43.5 44 0.5 8.03 0.49 and 44.5 45 0.5 13.94 0.43 and 45 45.5 0.5 2.36 and 45.5 46 0.5 6.95 66.5 67.5 1 1.82 0.64 69 69.5 0.5 2.66 0.45
BMU-25-092 11.95 12.45 0.5 3.46 0.48 30 30.5 0.5 6.15 0.47 33.5 34 0.5 2.51 0.48 49.5 51.5 2 1.99 1.88 Including 49.5 50.5 1 2.33 0.97 and 50.5 51 0.5 2.01 0.48 58 64 6 9.32 5.64 Including 59.7 60.2 0.5 23.52 and 60.2 60.9 0.7 3.10 0.63 and 60.9 61.4 0.5 3.21 and 62 62.5 0.5 26.51 and 63 63.5 0.5 51.09 79 79.5 0.5 4.80 0.35 88 90 2 3.31 1.93 Including 88 88.5 0.5 2.40 and 89.5 90 0.5 10.82 0.48 92.75 96 3.25 7.91 3.09 Including 92.75 93.25 0.5 20.81 0.48 and 93.25 93.75 0.5 1.83 0.45 and 93.75 94.25 0.5 6.20 0.43 and 94.25 94.75 0.5 3.39 0.49 and 95.5 96 0.5 18.58 0.49
BMU-25-093 27.15 30.65 3.5 2.29 3.45 Including 27.15 27.65 0.5 7.31 0.49 and 29.15 30.15 1 3.45 0.98 82.5 83 0.5 2.08 0.47 91.6 92.6 1 2.53 0.94 Including 92.1 92.6 0.5 4.65
BMU-25-094 33.9 34.9 1 3.23 0.83 Including 34.4 34.9 0.5 6.28 0.45 48.4 48.9 0.5 4.60 0.47 62.1 65.25 3.15 2.29 2.94 Including 62.1 62.6 0.5 4.90 0.48 and 62.6 63.1 0.5 2.38 0.45 and 63.1 63.6 0.5 3.62 0.43 and 63.6 64.5 0.9 1.86 0.87 68 68.5 0.5 17.63 0.48
BMU-25-095 7 10 3 1.83 2.90 Including 8 8.5 0.5 3.11 0.48 and 9 9.5 0.5 7.18 0.47 41.5 44.5 3 3.51 2.92 Including 41.5 42 0.5 9.54 0.49 and 42 42.5 0.5 2.80 0.49 and 44 44.5 0.5 6.39 0.47 61.4 63.4 2 2.39 1.95 Including 61.9 62.4 0.5 6.26 0.50 and 62.9 63.4 0.5 2.63 0.47 70.5 71 0.5 2.19 0.50
BMU-25-096 72 75.5 3.5 3.89 3.29 Including 73 73.5 0.5 3.49 0.47 and 74.5 75 0.5 14.78 0.47 and 75 75.5 0.5 8.14 80.75 83 2.25 3.93 1.87 Including 80.75 81.25 0.5 14.54 0.33 and 82 82.5 0.5 2.12 0.47

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	Drillhole ID	From (m)	To (m)	Length (m)	Au (g/t)	Est. True Width (m)
BMU-25-097 37.8 38.8 1 2.50 0.94 Including 38.3 38.8 0.5 4.49 0.47 62 62.5 0.5 3.72 0.48
BMU-25-098 7 10 3 2.76 2.72 Including 7.5 8 0.5 14.84 0.47 14.65 15.65 1 3.65 0.94 Including 14.65 15.15 0.5 7.05 0.47 39.5 43 3.5 6.28 3.23 Including 39.5 40 0.5 30.60 0.46 and 40 40.5 0.5 11.88 0.45 45 45.5 0.5 3.85 0.48 53.2 55.5 2.3 2.78 1.63 Including 54.5 55 0.5 11.64 0.41 62.05 66 3.95 2.27 3.71 Including 62.55 63.1 0.55 4.33 0.52 and 63.1 63.6 0.5 8.03 and 65.5 66 0.5 4.16 0.47
BMU-25-099 24.1 24.6 0.5 23.97 0.45 28.4 29.4 1 5.13 0.71 Including 28.9 29.4 0.5 10.10 0.35 80 80.5 0.5 2.33 0.43 103 103.5 0.5 2.17 0.35
BMU-25-100 14.5 15 0.5 2.16 0.43 18.25 19.75 1.5 2.23 1.41 Including 18.25 18.75 0.5 5.68 0.47 38.3 39.3 1 1.96 0.77 Including 38.3 38.8 0.5 2.82 0.38 52 53 1 2.05 0.91 Including 52 52.5 0.5 3.72 0.45 56 56.5 0.5 11.11 0.50 61.5 65 3.5 2.17 3.42 Including 61.5 62 0.5 10.44 0.47 and 62.5 63 0.5 2.11 0.50 66.5 67 0.5 4.01 0.50
BMU-25-101 15 19 4 7.32 3.94 Including 16.5 17 0.5 52.72 0.50 and 17.5 18 0.5 1.87 0.47 35.5 38 2.5 2.34 2.47 Including 36 36.5 0.5 4.83 0.50 and 37 37.5 0.5 2.64 0.49 and 37.5 38 0.5 2.52 0.49 39.5 40.5 1 3.97 0.97 Including 39.5 40 0.5 7.62 0.48 46.3 48.35 2.05 3.14 2.03 Including 46.8 47.3 0.5 1.88 0.49 and 47.85 48.35 0.5 10.74 0.50
BMU-25-102 7.5 9.5 2 4.67 1.98 Including 7.5 8 0.5 16.90 0.50 and 13.5 14 0.5 2.21 0.48 16 20 4 1.83 3.94 Including 16.5 17 0.5 5.27 0.50 and 18 18.5 0.5 3.84 and 18.5 19 0.5 2.79 0.49 41 41.5 0.5 2.75 0.45 54 54.5 0.5 3.52 0.49 81 82 1 2.85 0.94 Including 81.5 82 0.5 4.80 0.47
BMU-25-103 9 10 1 5.86 0.94 30.5 31 0.5 4.69 0.47 41.6 42.6 1 1.88 0.94 Including 41.6 42.1 0.5 2.22 0.43 46 46.5 0.5 2.46 0.41 53.25 54.85 1.6 7.00 1.56 Including 53.25 53.75 0.5 18.84 0.50 and 54.35 54.85 0.5 3.58 0.47 58 59.5 1.5 2.71 1.23 Including 58 58.5 0.5 5.77 0.41

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