6-K

UNITEDSTATESSECURITIES AND EXCHANGE COMMISSIONWashington, D.C. 20549

FORM6-K

REPORTOF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16 OR15d-16 UNDER THE SECURITIES EXCHANGE ACT OF 1934

Forthe month of December 2025

Commission File Number: 001-40786

SigmaLithium Corporation

(Translation of registrant's name into English)

181,Bay Street, Suite 4400Toronto, Ontario, M5J 2T3, Canada

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F [   ]      Form 40-F [X]

EXHIBITINDEX

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

SIGMA LITHIUMHIGHLIGHTS BRAZIL’S LEADERSHIP IN SUSTAINABLE LITHIUM AT COP30; ENGAGES IN HIGH-LEVEL GLOBAL DIALOGUES ON ENERGY TRANSITION, CRITICALMINERALS AND ESG INNOVATION

HIGH****LIGHTS

São Paulo, December1, 2025. Sigma Lithium Corporation (TSXV/NASDAQ: SGML, BVMF: S2GM34), a leading global lithium producer dedicated to powering the next generation of electric batteries with carbon neutral, socially and environmentally sustainable lithium concentrate, strengthened its role as an international reference in sustainable mining by participating in high-level policy, climate and industry discussions at COP30 in Belém, Brazil.

Across multiple official panels, ministerial dialogues, academic forums and sector roundtables, Sigma Lithium reinforced that Brazil has the conditions to lead the global sustainable lithium market, combining resource abundance, a mature industrial base, strong ESG standards and a unique model of socio-environmental responsibility developed in the Jequitinhonha Valley.

ENGAGED INHIGH-LEVEL GLOBAL ENERGY TRANSITION DIALOGUES AT COP30

Sigma Lithium’s senior executives — including Co-Chair and CEO Ana Cabral, Vice President of Sustainability Lígia Pinto, and Vice President of Business Development and International Affairs Daniel Abdo — participated throughout COP30 in key sessions focused on sustainable mineral supply chains, energy transition, and climate-aligned industrial development.

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| --- | | § | ICOPFireside – Frameworks That Deliver: During this conversation, Ana Cabral underscored the importance of transparency, tax incentives<br>and robust disclosure standards as essential tools to enable climate-aligned capital flows and strengthen investor confidence in the transition<br>to a low-carbon economy. | | --- | --- | | § | WorldClimate Foundation – Financing the Future: Sovereign Risk & Resilience: In this session, Lígia Pinto discussed how<br>climate shocks influence sovereign risk, reinforcing the central role of ESG data, ecosystem restoration and long-term climate planning<br>in supporting financial stability and resilience. | | --- | --- | | § | MinisterialDialogue – Brazil MME, CEBRI & Global Clean Power Alliance: Daniel Abdo joined global stakeholders to address bottlenecks<br>in the supply of copper and lithium, exploring their implications for climate security and highlighting Brazil’s strategic potential<br>to lead clean-energy supply chains worldwide. | | --- | --- | | § | CasaDiálogo – Creating Value from Critical Minerals: Presenting Sigma Lithium’s Quintuple Zero ESG model, Ana Cabral<br>positioned the Company as an international benchmark for mining aligned with environmental protection, economic development and social<br>inclusion. | | --- | --- | | § | IBRAM& CNI – Critical Minerals for Economic Transformation: In dialogue with climate experts and government leaders, Daniel Abdo<br>reinforced the strategic relevance of lithium for electric mobility, renewable energy storage and global energy-transition strategies,<br>underscoring Sigma Lithium’s role in this transformation. | | --- | --- |

Beyond these key engagements, Sigma Lithium’s executives also participated in a series of additional COP30 sessions across the Blue Zone and government pavilions, strengthening the Company’s dialogue with policymakers, multilateral institutions, industry leaders and civil society. These engagements further reinforced Sigma Lithium’s role as a trusted partner in advancing responsible mineral supply chains and supporting Brazil’s leadership in the global energy transition.

At the conclusion of the Company’s participation at COP30, Ana Cabral commented: “At COP30, we see clearly that the future of the energy transitiondepends on responsible, low-carbon supply chains for critical minerals. Brazil has the resources, talent and capability to lead this transformation.Sigma Lithium is proud to demonstrate that it is possible to produce lithium at scale with zero tailings dams, zero hazardous chemicalsand zero use of potable water — while generating long-term value for the communities of the Jequitinhonha Valley.”

ABOUT SIGMALITHIUM

Sigma Lithium (NASDAQ: SGML, TSXV: SGML, BVMF: S2GM34) is a leading global lithium producer dedicated to powering the next generation of electric batteries with carbon neutral, socially and environmentally sustainable lithium oxide concentrate.

The Company operates one of the world’s largest lithium production sites—the fifth-largest industrial-mineral complex for lithium oxide—at its Grota do Cirilo Operation in Brazil. Sigma Lithium is at the forefront of environmental and social sustainability in the electric battery materials supply chain, producing Quintuple Zero Green Lithium: zero coal power, zero tailings dams, zero utilization of potable water, zero use of hazardous chemicals and zero accidents.

Sigma Lithium currently produces 270,000 tonnes of lithium oxide concentrate on an annualized basis (approximately 38,000–40,000 tonnes of LCE) at its state-of-the-art Greentech Industrial Lithium Plant. The Company is now constructing a second plant to double production capacity to 520,000 tonnes of lithium oxide concentrate (approximately 77,000–80,000 tonnes of LCE).

For more information about Sigma Lithium, visit our website

FOR ADDITIONAL INFORMATION PLEASECONTACT

Anna Hartley, Vice President Investor Relations

anna.hartley@sigmalithium.com.br

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SigmaLithium

FORWARD-LOOKINGSTATEMENTS

Thisnews release includes certain “forward-looking information” under applicable Canadian and U.S. securities legislation, includingbut not limited to statements relating to timing and costs related to the general business and operational outlook of the Company, theenvironmental footprint of tailings and positive ecosystem impact relating thereto, donation and upcycling of tailings, timing and quantitiesrelating to tailings and Green Lithium, achievements and projections relating to the Zero Tailings strategy, achievement of ramp-up volumes,production estimates and the operational status of the Grota do Cirilo Project, and other forward-looking information. All statementsthat address future plans, activities, events, estimates, expectations or developments that the Company believes, expects or anticipateswill or may occur is forward-looking information, including statements regarding the potential development of mineral resources and mineralreserves which may or may not occur. Forward-looking information contained herein is based on certain assumptions regarding, among otherthings: general economic and political conditions; the stable and supportive legislative, regulatory and community environment in Brazil;demand for lithium, including that such demand is supported by growth in the electric vehicle market; the Company’s market positionand future financial and operating performance; the Company’s estimates of mineral resources and mineral reserves, including whethermineral resources will ever be developed into mineral reserves; and the Company’s ability to operate its mineral projects includingthat the Company will not experience any materials or equipment shortages, any labour or service provider outages or delays or any technicalissues. Although management believes that the assumptions and expectations reflected in the forward-looking information are reasonable,there can be no assurance that these assumptions and expectations will prove to be correct. Forward-looking information inherently involvesand is subject to risks and uncertainties, including but not limited to that the market prices for lithium may not remain at current levels;and the market for electric vehicles and other large format batteries currently has limited market share and no assurances can be givenfor the rate at which this market will develop, if at all, which could affect the success of the Company and its ability to develop lithiumoperations. There can be no assurance that such statements will prove to be accurate, as actual results and future events could differmaterially from those anticipated in such statements. Accordingly, readers should not place undue reliance on forward-looking information.The Company disclaims any intention or obligation to update or revise any forward-looking information, whether because of new information,future events or otherwise, except as required by law. For more information on the risks, uncertainties and assumptions that could causeour actual results to differ from current expectations, please refer to the current annual information form of the Company and other publicfilings available under the Company’s profile atwww.sedarplus.com.

Neither the TSX VentureExchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibilityfor the adequacy or accuracy of this news release.

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