Osisko Development Provides Infill Drilling Update on Its 13,000-Meter Lowhee Program at Cariboo Gold Project; Intercepts Include 596.40 g/t Gold Over 2.0 Meters from 6.1 Meters Downhole, Including 2,293.56 g/t Gold Over 0.5 Meters from 6.6 Meters Downhole

Press Release

HIGHLIGHTS

• 11,025 m of infill drilling completed (5,043 m new results) on 10-m drill spacing in 116 drill holes from August 2025 representing ~80% of the total planned ~13 km infill program
• Highlight intercepts include: 596.40 g/t Au over 2.0 m from 6.1 m downhole (including 2,293.56 g/t Au over 0.5 m from 6.6 m downhole), 21.67 g/t Au over 3.5 m from 96.5 m downhole (including 135.44 g/t Au over 0.5 m from 99.5 m downhole), and 21.97 g/t Au over 2.5 m from 48.7 m downhole
• Results to date continue to contribute to a more detailed understanding of spatial controls and local variability of the Lowhee Zone
• An aggregate total of ~12.1 km (~88%) of total planned drill meters have been completed to date, with full assays and QA/QC pending for the remaining, unreported holes
• Infill program anticipated to conclude in early Q2 2026

MONTREAL, Feb. 11, 2026 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 ~5,043 meters (“m”) of underground infill drilling, bringing the total tally of drilling with full results to 11,025 m, or ~80% of the planned total.

Chris Lodder, President, stated, “This tighter drill spacing gives us a better understanding of vein corridor spatial geometries and local variability specific to this part of the Lowhee deposit, while reinforcing the importance of continued drilling in underexplored zones. As this work concludes, the resulting information is expected to help refine infill drill requirements and production designs and sequencing in the Lowhee Deposit of the Cariboo Gold Project.”

In total, an aggregate of approximately 12.1 kilometres (“km”), representing ~88% 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. Infill drilling activities were suspended following the incident reported on January 23, 2026, with the program now anticipated to conclude in early Q2 2026.

DRILL ASSAY HIGHLIGHTS

This news release includes assays from fifty-four (54) underground infill HQ diamond drill (“DD”) holes (63.5-millimeter diameter) totaling 5,043 m with depths ranging from 51 to 117 m completed between mid-October 2025 and December 2025 (see Table 1). Assays for six (6) complete drill fans were received by January 11, 2026 (Figure 2). Select photon assay highlights include:

• 596.40 (“g/t”) gold (“Au”) over 2.0 m in BMU-25-132 from 6.1 m downhole, including:
  • 2,293.56 g/t over 0.5 m from 6.6 m downhole, and
  • 90.95 g/t over 0.5 m from 7.6 m downhole
• 21.67 g/t over 3.5 m in BMU-25-145 from 96.5 m downhole, including:
  • 135.44 g/t over 0.5 m from 99.5 m downhole, and
  • 11.88 g/t over 0.6 m from 97.0 m downhole

• 21.97 g/t over 2.5 m in BMU-25-174 from 48.7 m downhole, including:
  • 88.08 g/t over 0.5 m from 49.7 m downhole, and
  • 20.91 g/t over 0.5 m from 50.2 m downhole

• 9.21 g/t over 4.9 m in BMU-25-157 from 53.9 m downhole, including:
  • 39.26 g/t over 0.5 m from 54.9 m downhole, and
  • 19.10 g/t over 0.5 m from 55.9 m downhole, and
  • 15.95 g/t over 0.5 m from 55.4 m downhole, and
  • 6.88 g/t over 1.0 m from 53.9 m downhole
• 10.57 g/t over 4.8 m in BMU-25-157 from 84.9 m downhole, including:
  • 95.61 g/t over 0.5 m from 88.7 m downhole, and
  • 2.84 g/t over 0.5 m from 80.0 m downhole
• 10.48 g/t over 4.0 m in BMU-25-140 from 11.0 m downhole, including:
  • 54.01 g/t over 0.5 m from 12.4 m downhole, and
  • 28.34 g/t over 0.5 m from 11.9 m downhole
• 6.91 g/t over 4.5 m in BMU-25-145 from 90.0 m downhole, including:
  • 52.35 g/t over 0.5 m from 92.5 m downhole, and
  • 2.36 g/t over 0.7 m from 90.5 m downhole, and
  • 2.78 g/t over 0.5 m from 90.0 m downhole, and
  • 2.10 g/t over 0.5 m from 92.0 m downhole

• 5.94 g/t over 4.7 m in BMU-25-163 from 41.1 m downhole, including:
  • 18.91 g/t over 0.5 m from 43.65 m downhole, and
  • 14.44 g/t over 0.65 m from 45.15 m downhole, and
  • 8.94 g/t over 0.8 m from 42.0 m downhole, and
  • 2.47 g/t over 0.5 m from 44.15 m downhole
• 15.75 g/t over 1.95 m in BMU-25-148 from 108.1 m, including:
  • 30.84 g/t over 0.7 m from 108.1 m downhole, and
  • 11.18 g/t over 0.75 m from 109.3 m downhole
• 10.46 g/t over 3.0 m in BMU-25-134 from 81.4 m, including:
  • 51.40 g/t over 0.5 m from 82.9 m downhole, and
  • 8.10 g/t over 0.5 m from 81.4 m downhole

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, the above cut-off assay composites show a general spatial correlation with 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.
• Occurrences of above cut-off assays 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.

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