ATERRA Announces Completion of Totora Phase I Drill Program

ATERRA Metals Inc. (CSE: ATC) (OTCQB: CSSCF) ("ATERRA") is pleased to report that the Totora Cu-Au Project Phase I drill program has been finished with a total of 2,745.6 metres of drilling completed: 1,571.5 metres of reverse circulation and 1,174.1 metres of diamond drilling (Table 1). The Totora Cu-Au Project is located within the Dos Amigos Mining District, 60 kilometres south of the City of Vallenar, Region III, Chile, and 15 kilometres south of Tintina Mines' Domeyko Sulfuros Project (Figure 1).

The Phase I drilling program largely targeted the Totora and Algarrobilla Cu-Au porphyries with a single diamond drill collared into the Frontera Cu-Au deposit. The program comprised a combination of confirmational drilling in preparation for a resource estimate as well as exploration drilling to test the extensions of the known mineralized porphyries.

"The Phase I Totora drill program was safely completed on schedule," said Carl Hansen, CEO of ATERRA, "with drilling confirming the presence of pyrite and chalcopyrite mineralization at the Totora, Algarrobilla and Frontera porphyry systems. Unfortunately, due to a significant number of exploration and development programs currently underway in Chile, the assay laboratories are backed up and results are delayed 4 to 6 weeks. The delays should not impact our plans to have our first Totora Cu-Au Project resource estimate available during the third quarter of 2026."

Figure 1 - Totora Cu-Au Project Location - Dos Amigos Mining District

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Frontera Cu-Au Deposit

The Frontera Cu-Au Deposit hosts historic resources (Table 2) of 16 million indicated tonnes grading 0.56% copper equivalent ("CuEq") (0.38% copper and 0.22 grams per tonne gold) and 34 million inferred tonnes grading 0.54% CuEq (0.36% copper and 0.22 grams per tonne gold). The historical resource estimate was based on 16,175 metres of dominantly reverse circulation drilling, completed in 2013. ATERRA completed a single diamond drill hole into the Frontera to provide geological information and confirmatory assay data necessary for the preparation of a 43-101-compliant resource estimate. The diamond drill hole confirmed the presence of a mineralized quartz diorite porphyry (see figure 2).

Table 2 - Frontera Cu/Au Deposit: Historical Resource Estimate (March 2014)*

Figure 2 - Potassic-altered quartz diorite porphyry, Frontera Cu-Au Deposit, AFROD01

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Cautionary Note: While chalcopyrite mineralization has been observed in the diamond drill core and reverse circulation chips from the Phase I drill program, there can be no assurance that economically viable quantities of any metals are present. Assaying is necessary to determine grade and no grades should be inferred from the disclosure made in this press release.

Research Capital Advisory Agreement

On March 26, 2026, ATERRA announced that it had engaged Research Capital Corporation ("RCC") as a financial advisor for a period of 3 months. In consideration of RCC's engagement, ATERRA will issue RCC a total of 5,750,000 common shares of ATERRA, to be paid in 3 monthly tranches. The second tranche of 1,916,666 shares was issued effective May 26, 2026. The securities were issued at a deemed price of $0.0327 per share for total deemed consideration of $62,674.97. The shares issued are subject to a statutory hold period of 4 months (until August 27, 2026). Upon issuance of the shares to RCC, ATERRA will have 351,874,466 issued and outstanding common shares.

NI 43-101 Disclosure

Qualified Person: As defined by National Instrument 43-101 ("NI 43-101") of the Canadian Securities Administrators, the "Qualified Person" for ATERRA Metals Inc. is Francisco Bravo, a resident of Santiago, Chile. As ATERRA's Chief Geologist, Mr. Bravo is considered "not independent" as the term is defined by NI 43-101. Mr. Bravo, a Public Registered Person for Reserves and Resources N° 515, in Chile, and registered in the Colegio de Geólogos de Chile under N° 725, has reviewed and approved the technical information contained in this press release.

Copper Equivalent Estimation: Copper equivalent ("CuEq") grades were estimated using a copper price of US$4.00 per pound and a gold price of US$3,500 per ounce (US$112.53 per gram). CuEq grades are estimated using the following formula: CuEq% = (((Au grade * 0.85 * 112.53) / 4.00 / 2,204.6) * 100) + (Cu grade * 0.85).

Regulatory requirements for disclosure of CuEq grades require an estimation of metallurgical recoveries in the situation where no metallurgical testwork has been completed. ATERRA estimates copper recoveries of 85% and gold recoveries of 85%. Note that the actual recoveries will likely vary from those used in the estimation of the CuEq grades.

Historical Results: ATERRA's Qualified Person has not done sufficient work to make the Frontera Deposit resource estimate current and ATERRA does not consider the historical resource a current 43-101-compliant resource estimate. The reader is cautioned against relying on the accuracy of the historical results presented herein. ATERRA considers all historical results relevant as those results will be used as a guide to plan future exploration programs: ATERRA considers the data to be reliable for these purposes.

About ATERRA Metals Inc.

ATERRA is a mineral exploration company focused on exploration opportunities in Chile. ATERRA's team of successful exploration professionals is dedicated to the discovery of mineral deposits that can be progressed into economically viable development projects, creating value for all stakeholders.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This news release contains forward-looking statements, including predictions, projections and forecasts. Forward-looking statements include, but are not limited to: plans for the evaluation of exploration properties; the success of evaluation plans; the success of exploration activities; mine development prospects; and, potential for future metals production. Often, but not always, forward-looking statements can be identified by the use of words such as "plans", "planning", "expects" or "does not expect", "focus is to", "continues", "scheduled", "estimates", "forecasts", "objectives", "intends", "potential", "anticipates", "does not anticipate", or describes a "goal", or variation of such words and phrases or state that certain actions, events or results "may", "could", "would", "might", or "will" be taken, occur or be achieved.

Forward-looking statements involve known and unknown risks, future events, conditions, uncertainties and other factors which may cause the actual results, performance or achievements to be materially different from any future results, prediction, projection, forecast, performance or achievements expressed or implied by the forward-looking statements. Such factors include, among others: changes in economic parameters and assumptions; all aspects related to the timing of exploration activities and receipt of exploration results including assays; the interpretation and actual results of current exploration activities; changes in project or exploration parameters as plans continue to be refined; the results of regulatory and permitting processes; future metals prices; possible variations in grade or recovery rates; variations in the recovery rates used in the calculation of equivalent grades; failure of equipment or processes to operate as anticipated; labour disputes and other risks of the mining industry; the results of economic and technical studies; delays in obtaining governmental approvals or financing or in the completion of exploration; as well as those factors disclosed in ATERRA's publicly filed documents.

Although ATERRA has attempted to identify important factors that could cause actual actions, events or results to differ materially from those described in forward-looking statements, there may be other factors that cause actions, events or results not to be as anticipated, estimated or intended. There can be no assurance that forward-looking statements will prove to be accurate, as actual results and future events could differ materially from those anticipated in such statements. Accordingly, readers should not place undue reliance on forward-looking statements.

Neither the Canadian Securities Exchange nor its regulation services provider has reviewed or accepts responsibility for the adequacy or accuracy of the content of this news release.

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