IAMGOLD Corporation (NYSE: IAG) (TSX: IMG) is pleased to announce an updated Mineral Resource estimate for the Côté Gold Mine, located in Ontario, Canada, prepared in accordance with National Instrument 43-101 – Standards of Disclosure for Mineral Projects. The updated estimate, with an effective date of March 31, 2026, reflects the integration of the Côté and Gosselin zones into a consolidated block model with updated economic assumptions, ahead of the upcoming Côté expansion technical report and updated mine plan which is expected to be completed in the fourth quarter of 2026. Côté Gold is operated by IAMGOLD in a 70|30 joint venture with Sumitomo Metal Mining Co. Ltd.

Highlights

• Côté Gold Measured and Indicated Mineral Resources (100% basis) on a consolidated basis of 20.3 million ounces of gold, an increase of approximately 2.2 million ounces, or 12%, compared with the Dec. 31, 2025 statement.
  • Côté: M&I Mineral Resources (100% basis, inclusive of Mineral Reserves) of 12.7 million ounces of gold, an increase of approximately 1.5 million ounces, or 13%, compared with the Dec. 31, 2025 statement.
  • Gosselin: M&I Mineral Resources (100% basis) of 7.4 million ounces of gold, an increase of approximately 0.6 million ounces, or 8%, compared with the Dec. 31, 2025 statement.
  • The consolidated model allowed for increased delineation of the saddle area between the Côté and Gosselin zones, with an additional 0.2 million ounces of Indicated Mineral Resources.
• Inferred Mineral Resources (100% basis) on a consolidated basis of 3.5 million ounces of gold, an increase of approximately 1.3 million ounces, or 61%, compared with the Dec. 31, 2025 statement.
  • Côté: Inferred Mineral Resources (100% basis) of 2.0 million ounces of gold, an increase of approximately 0.8 million ounces, or 63%, compared with the Dec. 31, 2025 statement.
  • Gosselin: Inferred Mineral Resources (100% basis) of 0.9 million ounces of gold, a decrease of approximately 0.1 million ounces, or -7%, compared with the Dec. 31, 2025 statement.
  • The consolidated model allowed the addition of 0.6 million new Inferred ounces in the saddle area.
• Updated Mineral Resource estimate integrates the Côté and Gosselin zones, including the connecting saddle area, into a single geological and resource framework.
• Updated assumptions include a gold price of $2,500 per ounce (up from $2,100/oz for Côté and $2,500/oz for Gosselin in the prior statement) and a consolidated Mineral Resource cut-off grade of 0.25 g/t Au (down from 0.30 g/t Au previously) applied across the consolidated zones.
• The updated Mineral Resource estimate will inform the upcoming Côté Gold Technical Report and mine plan, which remains on track for announcement in the fourth quarter of 2026. The mine plan is expected to evaluate a plant expansion and a larger-scale mining scenario targeting the consolidated Côté and Gosselin resource model.

“This updated mineral resource estimate combines the Côté and Gosselin zones within a single geological framework, an important technical milestone as we move toward the expansion study and updated mine plan expected in the fourth quarter,” said Renaud Adams, President and Chief Executive Officer of IAMGOLD. “Our teams have done an excellent job building confidence in the resource through the 2025 drilling programs, and we are encouraged with the continued growth and conversion of ounces. As previously communicated to the market, the year-end technical report and mine plan will assess an expansion of the Côté Gold mine that brings the consolidated Côté and Gosselin zones into an integrated mine plan.”

Consolidated Côté and Gosselin Block Model

The updated Mineral Resource estimate is based on extensive diamond drilling and refined geological interpretations to better define the geometry and continuity of mineralization across the combined Côté and Gosselin zones.

Subsequent to the previous 2025 EOY MRMR statement, additional assays were received from 64 holes in both the Côté and Gosselin zones. In Côté, 39 additional drill holes were added, totaling 20,624 metres, mainly focused in the saddle area to further increase confidence in geological model in this area, adding resources in both indicated and inferred categories. In Gosselin, 25 additional drill holes were added within the resource pit, totaling 14,110 metres, mainly focused on the continued conversion of resources from inferred to indicated. These drill holes have been included in the consolidated model and updated resource estimate.

The estimate incorporates updates to the block model and estimation parameters, and reflects revised economic assumptions, including a gold price assumption of $2,500 per ounce and a cut-off grade of 0.25 g/t Au, replacing the prior bifurcated assumptions ($2,100/oz at Côté and $2,500/oz at Gosselin) and prior cut-off grade of 0.30 g/t Au. The modelling approach considers distinct mineralization domains and applies standard data processing techniques, including grade capping and compositing, prior to estimation within a three-dimensional block model.

Mineral Resources are classified according to confidence levels supported by drill spacing and data quality. Mineral Resources are constrained within an optimized open pit shell and are reported above a 0.25 g/t Au cut-off grade, reflecting reasonable prospects for eventual economic extraction. The estimate has been prepared in accordance with National Instrument 43-101 and CIM Definition Standards.

TABLE 1: CÔTÉ GOLD CONSOLIDATED MINERAL RESOURCE ESTIMATE
CÔTÉ + GOSSELIN ZONES

Figure 1 – Côté Gold Longitudinal Section of 2026 Resource Shell and Mineralization

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Figure 2 – Coté Gold Inclined View of Mineral Resources within 2026 Resource Shell and Mineralization

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Variance Analysis

Compared with the Mineral Resource statement effective December 31, 2025, the updated total Mineral Resource estimate for the consolidated Côté and Gosselin zones reflects an increase of approximately 148.5 Mt and 2.2 million ounces of contained gold in the M&I category, and an increase of approximately 76.5 Mt and 1.3 million ounces in the Inferred category. The increase in Measured and Indicated Mineral Resources was primarily driven by an increase in the gold price assumption for the Côté zone (from $2,100/oz to $2,500/oz) and an increase in ounces from the consolidated block model (refer to Figure 3 – Waterfall Reconciliation of Consolidated Measured and Indicated Resources). From a model consolidation perspective, the optimized resource shell allowed to add volume between the two zones in the Saddle Area, as well gain volume near the surface of Côté, with minimal losses at depth.

TABLE 2: MINERAL RESOURCE ESTIMATES VARIANCE – MARCH 31, 2026 VS. DEC. 31, 2025
(100% BASIS)¹,²

Figure 3 – Waterfall Reconciliation of Consolidated Measured and Indicated Mineral Resources

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Path Forward – Technical Report and Updated Mine Plan

The updated Mineral Resource estimate forms the technical foundation for the Company’s ongoing work on the expansion mine plan and accompanying Technical Report for Côté Gold, which is expected to be delivered in the fourth quarter of 2026. The Technical Report will outline an updated life-of-mine plan incorporating the consolidated Côté and Gosselin pit, evaluate options for a plant expansion to leverage the larger consolidated resource base, and update Mineral Reserves accordingly. Further details on the design, scheduling, and economic parameters of the integrated operation will be disclosed at that time.

The Company is planning an additional 30,000 m diamond drilling program for 2026. The next phases of diamond drilling will aim to infill and test the ability to further expand the mineralized envelope for 2027. Drilling and technical studies are continuing at Côté Gold in 2026, with the objectives of further upgrading Inferred Mineral Resources and supporting the integrated mine planning work underway.

District Exploration

The Côté Gold property includes a large and prospective regional land package that offers considerable exploration targets. Near-mine opportunities along the Côté-Gosselin structural corridor, including the Clam Lake and Jack Rabbit extensions, offer potential to extend mineralization to the northeast and southwest through Côté-style tonalite- and diorite-hosted breccia zones. Regionally, the 25-kilometre Swayze West land package hosts a favorable structural setting for higher-grade, potentially underground deposits and will be tested over the next two to three years, including targets at the historic Jerome deposit and the neighboring Northshore, Monella Point and other prospects. Collectively, these targets support the view that the broader Côté Gold district has the potential to host additional deposits that could, if successful, complement the existing operation.

Figure 4 – Côté Gold Regional Geology and Exploration Targets

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Qualified Person and Technical Information

The 2026 Mineral Resource Estimate results contained in this news release have been prepared by SLR Consulting (Canada) Ltd., in accordance with NI 43-101 – Standards of Disclosure for Mineral Projects.

Denis Decharte, P.Eng., Consultant Resource Geologist, SLR Consulting (Canada) Ltd., is the independent Qualified Person for the purposes of NI 43-101 with respect to the mineralization being reported on, and has prepared, reviewed, verified and approved the scientific and technical information relating to the Mineral Resource Estimates presented herein.

Christine Beausoleil, P.Geo., Senior Director, Mining Geology, IAMGOLD Corporation is the Qualified Person for the purposes of NI 43-101 with respect to the mineralization being reported on and is responsible for the review and approval of all Mineral Resource estimates for IAMGOLD.

Marie-France Bugnon, P.Geo., Vice President, Exploration, IAMGOLD Corporation is the Qualified Person for the purposes of NI 43-101 with respect to exploration activities reported on, and has prepared, reviewed, verified and approved the scientific and technical information disclosed in this document.

About IAMGOLD

IAMGOLD is an intermediate gold producer and developer based in Canada with operating mines in North America and West Africa, including Côté Gold (Canada), Westwood (Canada) and Essakane (Burkina Faso). The Côté Gold Mine is among the largest gold mines in production in Canada, which IAMGOLD operates in a 70|30 partnership with Sumitomo Metal Mining Co. Ltd. In addition, the Company has an established portfolio of early stage and advanced exploration projects within high potential mining districts, including the large-scale Nelligan Mining Complex located in Quebec, Canada. IAMGOLD employs approximately 3,700 people and is committed to maintaining its culture of accountable mining through high standards of Environmental, Social and Governance practices. IAMGOLD is listed on the New York Stock Exchange (NYSE: IAG) and the Toronto Stock Exchange (TSX: IMG).