Osisko Development Extends GOLD Mineralization at Cariboo GOLD Project Beyond 700 M Vertical Depth IN Previously Untested Areas; Intercepts Include 13.19 G/T GOLD over 3.60 M at 596 M Vertical Depth and 28.90 G/T GOLD over 0.50 M at 718 M Vertical Depth

ODV NYSE TSXV News Release

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OSISKO DEVELOPMENT EXTENDS GOLD MINERALIZATION AT CARIBOO GOLD

PROJECT BEYOND 700 M VERTICAL DEPTH IN PREVIOUSLY UNTESTED AREAS;

INTERCEPTS INCLUDE 13.19 g/t GOLD OVER 3.60 M AT 596 M VERTICAL DEPTH

AND 28.90 g/t GOLD OVER 0.50 M at 718 M VERTICAL DEPTH

HIGHLIGHTS

 8,971 m of new surface exploration drilling designed to test near mine potential at depth and in

under-drilled gap zones between defined deposit footprints. Approximately 65% of drilling

transected areas outside the Cariboo Gold deposit.

 Highlight intercepts from outside the footprint of the current mineral resource across multiple zones on strike,

include: 13.19 g/t Au over 3.60 m at 596 m vertical depth, 6.40 g/t Au over 6.30 m at 326 m vertical

depth (including 40.60 g/t Au over 0.50 m, 19.10 g/t Au over 0.70 m, and 4.56 g/t Au over 0.70 m),

6.17 g/t Au over 7.10 m at 517 m vertical depth (including 73.20 g/t Au over 0.50 m, 10.40 g/t Au

over 0.50 m, and 2.21 g/t Au over 0.50 m) and 28.90 g/t Au over 0.50 m at 718 m vertical depth.

 Results to date confirm the presence of high-grade mineralization at depth and reinforce the strong

potential for upside within under -tested gap zones and below the current Cariboo Gold deposit

footprint, which extends to an average depth of approximately 350 metres.

 5 drill rigs continue operating at surface systematically testing targets down -dip of the current

Mineral Resource to a maximum vertical depth of up to 800 metres.

Montreal, Québec, July 8, 2026 – Osisko Development Corp. (NYSE: ODV, TSXV: ODV) ("Osisko

Development" or the "Company") is pleased to announce new drilling results from eleven (11) surface

diamond drill holes that were completed as part of an ongoing deeps and near mine gap infill exploration

program at the Company's permitted, 100%-owned Cariboo Gold Project (" CGP" or the " Project"),

located in central British Columbia, Canada.

Chris Lodder, President, stated, "We are encouraged by the initial results of the surface exploration

drill program at the Cariboo Gold Project, which intercepted mineralization in all eleven drill holes. Strong

high-grade intercepts in previously untested areas and known under-tested gaps continue to

demonstrate the at depth potential for resource growth beyond our current mineral inventory. These

results reinforce our view that we are only beginning to define the full extent of the mineralized system

at depth, while identifying compelling near-mine upside opportunities — all within the Project's existing

permitted footprint. We are at an early stage of this program and are excited to keep drilling."

DRILL ASSAY HIGHLIGHTS

This news release includes assays from eleven (11) surface deeps and gap zone exploration diamond

drill ("DD") holes totaling 8,971 metres ("m") with depths ranging from 114 to 1,159 m (see Table 1

and Figure 2) completed between December 2025 and April 2026. Approximately 65%, or 5,823 m of

drilling transected areas outside the current Cariboo Gold Mineral Resources, as defined by a 15 m buffer

around optimized Mineral Reserves and Mineral Resources stope shapes1. All holes were collared in HQ

(63.5 millimetre diameter) and reduced to NQ (47.6 millimetre diameter) where necessary to continue

advance or implement directional drilling. Available tooling for d irectional drilling requires advance in

NQ with a BQ (36.5 millimetre diameter) output while steering is active. All assays were received by

June 1, 2026 . Select assay highlights from intercepts outside the current Mineral Resources footprint

include:

• 42.42 grams per tonne ("g/t") gold ("Au") over 1.50 m in IM-26-001 at 111 m vertical

depth (Figure 2), including:

o 122.50 g/t Au over 0.50 m, and

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o 3.17 g/t Au over 0.50 m

• 6.40 g/t Au over 6.30 m in IM-26-001 at 326 m vertical depth, including:

o 40.60 g/t Au over 0.50 m, and

o 19.10 g/t Au over 0.70 m, and

o 4.56 g/t Au over 0.70 m

• 6.17 g/t Au over 7.10 m in IM-26-003 at 517 m vertical depth, including:

o 73.20 g/t Au over 0.50 m, and

o 10.40 g/t Au over 0.50 m, and

o 2.21 g/t Au over 0.50 m

• 13.19 g/t Au over 3.60 m in IM-26-003 at 596 m vertical depth, including:

o 73.10 g/t Au over 0.50 m, and

o 15.95 g/t Au over 0.50 m, and

o 2.25 g/t Au over 0.60 m, and

o 1.93 g/t Au over 0.50 m

• 4.87 g/t Au over 5.90 m in IM-26-003 at 524 m vertical depth, including:

o 29.00 g/t Au over 0.50 m, and

o 17.15 g/t Au over 0.50 m, and

o 4.56 g/t Au over 0.50 m, and

o 2.81 g/t Au over 0.50 m

• 6.61 g/t Au over 4.50 m in IM-26-003 at 425 m vertical depth (Figure 3), including:

o 41.00 g/t Au over 0.50 m, and

o 5.84 g/t Au over 0.50 m, and

o 4.40 g/t Au over 0.50 m, and

o 2.91 g/t Au over 0.50 m, and

o 2.24 g/t Au over 0.50 m

• 2.79 g/t Au over 8.25 m in IM-26-001 at 436 m vertical depth, including:

o 19.65 g/t Au over 0.50 m, and

o 9.30 g/t Au over 0.50 m, and

o 3.06 g/t Au over 0.50 m, and

o 6.36 g/t Au over 0.50 m, and

o 4.03 g/t Au over 0.50 m

• 13.83 g/t Au over 1.55 m in IM-26-003 at 277 m vertical depth, including:

o 38.70 g/t Au over 0.55 m

• 8.81 g/t Au over 2.25 m in CM-26-001 at 370 m vertical depth, including:

o 23.10 g/t Au over 0.50 m, and

o 16.00 g/t Au over 0.50 m

• 17.32 g/t Au over 1.00 m in CM-25-003 at 371 m vertical depth, including:

o 33.10 g/t Au over 0.50 m

Complete assay highlights, including true width estimates and vertical depths from surface , are

presented in Tables 1 and 2, split by relative position within and outside of the current footprint of the

Cariboo Gold Mineral Resources1. Drill hole locations and collar 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.

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Figure 1: Plan view Cariboo deep and gap zone surface drilling select intercept highlights.

Figure 2: 42.42 g/t Au over 1.50 m in IM-26-001 at 111 m vertical depth.

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Figure 3: 6.61 g/t au over 4.50 m in IM-26-003 at 425 m vertical depth.

Figure 4: 2.79 g/t Au over 8.25 m in IM-26-001 at 436 m vertical depth.

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Figure 5: Long section displaying Cariboo deeps and gap zone surface drilling with select intercept highlights.

DISCUSSION OF RESULTS

• Results to date confirm the presence of high-grade mineralization at depth and reinforce the

strong potential for resource growth upside well beyond the 350 m average of depth of the

current deposit.

• The consistency of broad high-grade intercepts in drill holes testing through and under the Shaft-

Mosquito Gap, as seen in IM-26-002 and IM-26-003 (Figure 5), suggests high potential for near

mine upside within this previously undertested zone.

• Significant number of intercepts in Table 1 (length weighted assay composites and individual

samples>=1.8 g/t Au within the footprint of the current Mineral Resources) demonstrate notable

continuity and possible resource upside potential.

• All eleven holes released encountered assay composites >=1.8 g/t Au, with t en holes

encountering assay composites >=1.8 g/t Au outside the current Mineral Resources. One hole

(CM-25-001) was stopped early at 11 4 m due to historical workings intercepted at 108 m

downhole.

ABOUT THE CARIBOO DEEP PROGRAM

This ongoing program is designed to test the potential for vein corridor extensions of the existing Cariboo

Gold deposit down to vertical depths of up to 800 m. The defined limit of the existing Cariboo Gold

Mineral Resources and Mineral Reserves reflects limitations imposed by local topograph y and the

practical depth of surface drills for achieving intercept spacing required for a mineral resource estimate,

which is approximately 350 m vertical on average across the 4.4 km strike of the deposit. The program

is also designed to target under-tested gap areas between defined deposit zones where historic mining

was observed, including, for example, the ~1.2 km gap between the Shaft and Mosquito Creek Zones.

Drillholes collared within the defined resource provide additional infill intercepts at shallower depths .

Directional drilling has been implemented on select drillholes for higher precision targeting to depth.

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Ongoing surface drilling will continue to systematically test down-dip of the current resource to a

maximum along strike target spacing of 300 m. Additional holes at target spacing 50 m near surface

and 100 m at depth will be drilled to test continuity around the most prospective intercepts outside the

current Mineral R esources footprint. New lithologic data incorporated into updated and extended

geologic models is expected to aid in further refining of at depth targets.

Table 1: Length weighted assay composites and individual samples>=1.8 g/t for Cariboo Deep diamond drill

intercepts within the footprint of the current resource.

Drillhole ID From (m) To (m) Length (m) Au g/t

Est. True

Width (m)

Vertical

Depth (m)

CM-25-001 100.30 104.25 3.95 2.73 2.54 78

Including 102.65 103.75 1.10 8.68

CM-25-002 65.40 65.90 0.50 1.91 0.35 51

101.80 104.80 3.00 2.74 2.12 80

Including 101.80 103.30 1.50 3.24

and 103.30 104.80 1.50 2.23

177.10 180.50 3.40 9.31 2.30 140

Including 177.10 177.60 0.50 2.57

and 177.60 178.10 0.50 38.10

and 179.50 180.00 0.50 16.25

and 180.00 180.50 0.50 3.03

187.25 187.80 0.55 9.30 0.39 147

191.70 196.20 4.50 4.41 3.18 153

Including 193.70 194.20 0.50 12.75

and 195.70 196.20 0.50 25.00

208.00 211.75 3.75 3.63 2.41 166

Including 209.00 209.50 0.50 24.90

230.40 231.90 1.50 2.26 1.41 184

Including 230.90 231.40 0.50 6.45

233.50 234.00 0.50 16.05 0.50 186

235.00 236.00 1.00 17.47 0.42 188

Including 235.00 235.50 0.50 34.50

248.30 251.20 2.90 12.09 1.77 200

Including 249.70 250.45 0.75 26.50

and 250.45 251.20 0.75 19.60

264.90 266.90 2.00 12.83 1.41 214

Including 265.40 265.90 0.50 5.61

and 265.90 266.40 0.50 45.40

CM-25-003 86.50 87.00 0.50 3.19 0.25 72

142.35 142.85 0.50 3.10 0.25 117

178.85 179.85 1.00 1.83 0.77 147

Including 179.35 179.85 0.50 2.00

197.45 200.15 2.70 1.88 2.24 163

Including 199.65 200.15 0.50 8.22

215.30 215.80 0.50 1.87 0.35 177

248.70 249.70 1.00 2.44 0.91 204

Including 249.20 249.70 0.50 4.39

312.85 313.85 1.00 2.26 0.67 255

Including 312.85 313.35 0.50 4.21

321.40 322.40 1.00 2.11 0.71 262

Including 321.40 321.90 0.50 3.86

and 346.00 347.00 1.00 8.40 0.71 281

351.85 353.50 1.65 10.62 1.13 286

Including 351.85 353.00 1.15 15.20

355.90 357.00 1.10 3.35 0.90 290

Including 355.90 356.50 0.60 5.94

364.25 364.75 0.50 3.06 0.38 296

365.90 368.15 2.25 64.13 1.87 298

Including 367.65 368.15 0.50 288.00

392.05 392.55 0.50 2.34 0.39 320

CM-26-001 171.10 172.85 1.75 7.30 1.39 129

Including 172.35 172.85 0.50 24.90

198.80 199.80 1.00 2.06 0.64 149

Including 199.30 199.80 0.50 3.43

340.70 343.60 2.90 2.93 1.96 254

Including 340.70 341.85 1.15 5.61

and 341.85 342.55 0.70 2.45

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Drillhole ID From (m) To (m) Length (m) Au g/t

Est. True

Width (m)

Vertical

Depth (m)

344.75 346.20 1.45 2.20 0.98 257

Including 345.25 346.20 0.95 3.20

352.70 353.80 1.10 2.20 0.63 263

Including 353.20 353.80 0.60 3.81

and 356.10 356.60 0.50 2.81 0.41 265

473.75 474.75 1.00 1.88 0.76 356

Including 474.25 474.75 0.50 2.09

CM-26-002 35.40 36.55 1.15 5.76 0.74 15

Including 35.90 36.55 0.65 10.00

61.50 64.25 2.75 1.85 2.11 24

Including 62.00 62.50 0.50 9.38

73.00 74.40 1.40 3.49 1.03 28

Including 73.00 73.60 0.60 2.43

and 73.60 74.40 0.80 4.29

76.45 84.00 7.55 3.26 5.34 31

Including 77.45 77.95 0.50 2.06

and 78.45 79.50 1.05 13.10

and 80.10 81.00 0.90 8.55

92.85 97.00 4.15 5.30 3.99 36

Including 93.35 94.00 0.65 13.05

and 94.00 94.50 0.50 25.80

172.00 172.50 0.50 5.77 0.43 72

201.50 202.90 1.40 2.48 1.07 90

207.85 208.35 0.50 1.82 0.38 92

213.20 213.70 0.50 1.86 0.38 94

222.80 226.75 3.95 11.11 2.91 99

Including 223.55 224.05 0.50 66.80

and 224.55 225.05 0.50 16.85

232.90 234.00 1.10 2.19 0.71 102

Including 233.40 234.00 0.60 3.85

253.90 257.00 3.10 8.29 2.61 114

Including 253.90 254.40 0.50 2.97

and 254.40 254.90 0.50 45.00

and 254.90 255.40 0.50 3.14

261.25 264.30 3.05 3.37 1.96 118

Including 261.25 261.75 0.50 15.45

and 262.85 263.55 0.70 3.12

268.50 269.50 1.00 2.42 0.64 123

Including 269.00 269.50 0.50 4.60

305.30 305.80 0.50 10.60 0.32 145

319.00 322.00 3.00 5.50 2.12 154

Including 321.50 322.00 0.50 31.80

390.50 392.35 1.85 1.93 1.31 197

Including 390.50 391.00 0.50 5.35

410.00 418.00 8.00 2.41 6.13 212

Including 411.00 411.50 0.50 10.80

and 415.00 415.50 0.50 15.80

and 416.00 416.50 0.50 9.69

442.00 443.10 1.10 2.35 0.78 231

449.15 449.85 0.70 2.22 0.45 236

452.65 457.00 4.35 2.34 2.80 240

Including 456.40 457.00 0.60 16.25

458.30 461.85 3.55 12.30 2.91 243

Including 459.50 460.90 1.40 17.50

and 460.90 461.85 0.95 19.75

485.90 486.40 0.50 8.40 0.37 260

537.50 542.90 5.40 21.35 4.14 300

Including 540.65 541.15 0.50 3.15

and 541.15 542.40 1.25 89.80

CM-26-003 36.00 36.50 0.50 11.20 0.38 29

153.00 153.70 0.70 3.04 0.43 115

264.00 264.50 0.50 2.07 1.00 198

353.90 354.90 1.00 2.22 0.64 265

Including 353.90 354.40 0.50 4.10

373.00 374.00 1.00 2.28 0.82 279

377.00 377.50 0.50 2.09 0.32 281

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Drillhole ID From (m) To (m) Length (m) Au g/t

Est. True

Width (m)

Vertical

Depth (m)

IM-25-001 46.25 47.00 0.75 38.30 0.65 37

49.05 50.05 1.00 8.41 0.87 40

Including 49.05 49.55 0.50 16.70

93.00 94.70 1.70 2.74 1.60 84

Including 93.65 94.20 0.55 7.53

128.65 129.15 0.50 4.31 0.41 118

180.00 181.00 1.00 2.17 1.65 169

190.00 192.25 2.25 1.89 1.84 180

Including 190.70 191.20 0.50 3.96

and 191.75 192.25 0.50 4.03

248.50 249.00 0.50 2.02 0.32 237

296.60 297.60 1.00 2.02 0.57 285

Including 297.10 297.60 0.50 3.11

334.60 336.40 1.80 2.50 1.56 324

Including 334.60 335.20 0.60 5.42

340.45 352.50 12.05 5.07 7.47 335

Including 340.95 341.85 0.90 20.20

and 341.85 342.45 0.60 2.70

and 343.00 343.55 0.55 6.62

and 343.55 344.05 0.50 14.75

and 344.70 345.50 0.80 1.81

and 345.50 346.05 0.55 2.73

and 346.05 347.45 1.40 15.15

361.00 365.00 4.00 2.56 3.06 351

Including 361.50 362.00 0.50 16.20

and 363.00 363.55 0.55 2.68

371.85 372.85 1.00 2.47 0.69 360

Including 371.85 372.35 0.50 3.55

379.75 383.25 3.50 3.13 2.92 369

Including 379.75 380.25 0.50 3.57

and 380.25 380.75 0.50 3.55

and 381.25 381.75 0.50 4.52

and 381.75 382.25 0.50 5.93

and 382.25 382.75 0.50 4.05

399.05 401.05 2.00 9.11 1.65 388

Including 399.05 399.55 0.50 32.10

and 400.55 401.05 0.50 4.00

410.75 412.70 1.95 4.39 1.83 399

Including 410.75 411.25 0.50 5.91

and 411.25 412.20 0.95 5.80

516.75 517.75 1.00 1.83 0.77 504

Including 516.75 517.25 0.50 3.19

IM-26-001 237.00 238.50 1.50 2.13 1.36 215

456.55 457.10 0.55 2.64 0.44 401

IM-26-002 90.50 92.65 2.15 13.48 1.82 52

Including 90.50 91.00 0.50 55.60

152.20 153.70 1.50 1.85 1.23 93

Including 152.70 153.20 0.50 1.93

and 153.20 153.70 0.50 3.50

221.00 222.60 1.60 9.18 1.41 144

Including 221.00 221.50 0.50 25.80

and 221.50 222.00 0.50 3.29

241.40 243.70 2.30 5.05 1.99 161

Including 241.40 242.50 1.10 10.40

290.30 292.65 2.35 5.34 1.80 201

Including 290.30 291.50 1.20 9.48

306.75 309.75 3.00 4.14 2.57 214

Including 308.75 309.25 0.50 1.95

and 309.25 309.75 0.50 21.60

IM-26-004 56.15 59.05 2.90 1.81 2.22 53

Including 56.15 57.00 0.85 4.53

62.40 66.80 4.40 7.62 3.81 60

Including 62.40 63.40 1.00 1.84

and 64.15 64.65 0.50 2.41

and 64.65 65.15 0.50 58.30

73.20 74.70 1.50 11.58 1.15 69