ATERRA Metals Commences Preparation of Maiden Mineral Resource Estimate for the Totora Cu/Au Project

ATERRA Metals Inc. (CSE: ATC) (OTCQB: CSSCF) ("ATERRA" or the "Company") is pleased to announce that it has commenced preparation of the Company's maiden independent Mineral Resource Estimate ("MRE") for its Totora CuAu Project ("Totora" or the "Project"). The maiden MRE will define Totora's initial mineral inventory and establish the technical foundation for future economic studies. ATERRA has engaged SRK Consulting (Chile) SpA ("SRK"), a leading international mining consultancy, to prepare the independent MRE. The Project is located in the Dos Amigos Mining District, 15 kilometres south of Tintina Mines' Domekyo Sulfuros development project (see Figure 1).

The MRE will be prepared in accordance with Canadian Securities Administrators' National Instrument 43-101 - Standards of Disclosure for Mineral Projects ("NI 43-101") and will incorporate the results from ATERRA's recently completed Phase I drill program together with historical drilling completed on the Project. The estimate will focus on the Company's three principal copper-gold porphyry systems - Frontera, Totora and Clinton - which collectively represent the most advanced exploration targets on the property. It is anticipated that the MRE will be available for release during September 2026.

Carl Hansen, Chief Executive Officer of ATERRA, commented: "Our objective is to establish the first independently verified mineral resource at Totora by integrating the results from a number of historical drill programs with our successful Phase I drilling. A maiden resource will provide investors with the first quantitative assessment of the scale of the Project and guide ATERRA's future exploration and development plans. This work marks an important step toward unlocking the value of the Totora Project."

Mr. Hansen continued: "Recent investments by multiple companies in the Dos Amigos Mining District underscore renewed industry interest in the region's copper-gold potential. We believe this increasing activity highlights the strategic position of the Totora Project within an emerging mining district."

Phase I Totora Drilling Highlights

The Mineral Resource Estimate will incorporate the results of ATERRA's recently completed Phase I drill program at Totora, the highlights of which were previously disclosed in the Company's news release dated July 16, 2026. Selected drill highlights previously reported include:

• Frontera (AFROD01): 284 metres grading 0.64% CuEq (0.41% Cu & 0.27 g/t Au) from surface, including 180 metres grading 0.71% CuEq (0.48% Cu & 0.28 g/t Au); and

• Totora (ATOD01): 194 metres grading 0.41% CuEq (0.35% Cu & 0.11 g/t Au) from 254 metres downhole.

Figure 1 - Dos Amigos Mining District - Location of ATERRA Totora Cu/Au Project Properties

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NI 43-101 Disclosure

Qualified Person: As defined by 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 in Chile (N° 515) and registered with the Colegio de Geólogos de Chile (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).

NOTE: Regulatory requirements for disclosure of CuEq grade estimates 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%. It is important to note that actual recoveries will likely vary from those used in the estimation of the CuEq grades.

About ATERRA Metals Inc.

ATERRA Metals Inc. is a mineral exploration company focused on advancing high-quality copper and gold assets in the Americas. The Company's flagship Totora Cu/Au Project is located within Chile's highly prospective Dos Amigos Mining District and hosts multiple copper-gold porphyry systems with significant exploration and development potential.

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: timing of the release of the MRE; 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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