NiSource 10-K 2025-12-31

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 2025

OR

OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from to

Commission file number 001-16189

NiSource Inc.

(Exact name of registrant as specified in its charter)

(614) 460-6000

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes þ No ¨

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes ¨ No þ

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes þ No ¨

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes þ No ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definition of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and "emerging growth company" in Rule 12-b-2 of the Exchange Act.

Large accelerated filer þ Accelerated Filer ¨ Emerging Growth Company ☐ Non-accelerated Filer ¨ Smaller Reporting Company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. ☑

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrants included in the filing reflect the correction of an error to previously issued financial statements. ☐

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant's executive officers during the relevant recovery period pursuant to §240. 10D-1(b).☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes ☐ No þ

The aggregate market value of the registrant's common stock, par value $0.01 per share (the "Common Stock") held by non-affiliates was approximately $18,966,136,571 based upon the June 30, 2025, closing price of $40.34 on the New York Stock Exchange.

There were 478,533,171 shares of Common Stock outstanding as of February 4, 2026.

Documents Incorporated by Reference

Part III of this report incorporates by reference specific portions of the Registrant’s Notice of Annual Meeting and Proxy Statement relating to the Annual Meeting of Stockholders to be held on May 11, 2026.

CONTENTS

Note regarding forward-looking statements

This Annual Report on Form 10-K contains "forward-looking statements," within the meaning of Section 27A of the Securities Act of 1933, as amended (the "Securities Act"), and Section 21E of the Securities Exchange Act of 1934, as amended (the "Exchange Act"). These forward-looking statements include, but are not limited to, statements concerning our plans, strategies, objectives, expected performance, planned expenditures, recovery of expenditures through rates, stated on either a consolidated or segment basis, and any and all underlying assumptions and other statements that are not statements of historical fact. Expressions of future goals and expectations and similar expressions reflecting something other than historical fact, including "may," "will," "should," "could," "would," "aims," "seeks," "expects," "plans," "anticipates," "intends," "believes," "estimates," "predicts," "potential," "targets," "forecast," and "continue," are intended to identify forward-looking statements. All forward-looking statements are based on assumptions that management believes to be reasonable; however, there can be no assurance that actual results will not differ materially. Investors and prospective investors should understand that many factors impact whether any forward-looking statement contained herein will, or can be, realized. Any one of those factors could cause actual results to differ materially from those projected.

Factors that could cause actual results to differ materially from those projected in any forward-looking statement discussed in this Annual Report on Form 10-K include, among other things:

• our ability to execute our business plan or growth strategy, including utility infrastructure investments, or business opportunities;

• our ability to manage data center growth in our service territories;

• potential incidents and other operating risks associated with our business;

• our ability to work successfully with our JV partners;

• our ability to construct, develop and place into service the Contract Assets and any other generation or transmission assets we develop to support future data center contracts on time or at all and consistent with initial cost estimates, as well as the performance of such assets once constructed and placed into service;

• our ability to obtain the significant additional financing required to construct the Contract Assets and any other generation or transmission assets we develop to support future data center contracts on favorable terms, if at all;

• our ability to recover our investments and realize our expected return under the ADS Contract and any future data center contracts that we enter into;

• our ability to maintain our investment grade credit ratings as we finance and pursue our data center strategy, including our performance under the ADS Contract and any future data center contracts that we enter into;

• ADS’ performance under the ADS Contract and the performance of our customers under any future data center contracts;

• any decision by ADS to terminate or reduce the committed capacity under the ADS Contract or any decision by any customer under any future data center contract to terminate or reduce the committed capacity under the contract;

• potential changes in the MISO accreditation treatment of capacity resources;

• our ability to adapt to, and manage costs related to, advances in technology, including alternative energy sources and changes in related laws and regulations;

• our increased dependency on technology;

• impacts related to our aging infrastructure;

• our ability to obtain sufficient insurance coverage and whether such coverage will protect us against significant losses;

• the success of our electric generation strategy;

• construction risks and supply risks;

• fluctuations in demand from residential and commercial customers;

• fluctuations in the price of energy commodities and related transportation costs or an inability to obtain an adequate, reliable and cost-effective fuel supply to meet customer demand;

• our ability to attract, retain or re-skill a qualified, workforce and maintain good labor relations;

• our ability to manage new initiatives and organizational changes;

• the performance and quality of third-party suppliers and service providers;

• our ability to manage the financial and operational risks related to achieving our carbon emission reduction goals, including our Net Zero Goal (as defined below), including any future associated impact from business opportunities such as data center development as those opportunities evolve;

• regulation and the impact of regulatory rate reviews;

• our ability to obtain expected financial or regulatory outcomes;

• potential cybersecurity attacks or security breaches;

• increased requirements and costs related to cybersecurity;

• any damage to our reputation;

• the impacts of natural disasters, potential terrorist attacks or other catastrophic events;

• the physical impacts of climate change and the transition to a lower carbon future;

• our debt obligations;

• any changes to our credit ratings or the credit ratings of certain of our subsidiaries;

• adverse economic and capital market conditions, including increases in inflation or interest rates, recession, or changes in investor sentiment;

• the actions of activist stockholders;

• economic conditions in certain industries;

• the ability of customers and suppliers to fulfill their payment and contractual obligations;

• the ability of our subsidiaries to generate cash;

• pension funding obligations;

• potential impairments of goodwill;

• the outcome of legal and regulatory proceedings, investigations, incidents, claims and litigation;

• compliance with changes in, or new interpretations of applicable laws, regulations and tariffs;

• the cost of compliance with environmental laws and regulations and the costs of associated liabilities;

• changes in tax laws or the interpretation thereof; and

• other matters set forth in Part I. Item 1, "Business," Part I, Item 1A, "Risk Factors" and Part II, Item 7, "Management’s Discussion and Analysis of Financial Condition and Results of Operations," of this report, some of which risks are beyond our control.

In addition, the relative contributions to profitability by each business segment, and the assumptions underlying the forward-looking statements relating thereto, may change over time.

All forward-looking statements are expressly qualified in their entirety by the foregoing cautionary statements. We undertake no obligation to, and expressly disclaim any such obligation to, update or revise any forward-looking statement to reflect changed assumptions, the occurrence of anticipated or unanticipated events or changes to expected results over time or otherwise, except as required by law.

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PART I

Business

NiSource Inc. is an energy holding company under the Public Utility Holding Company Act of 2005 whose primary subsidiaries are fully regulated natural gas and electric utility companies, serving approximately 3.8 million customers in six states. NiSource is the successor to an Indiana corporation organized in 1987 under the name of NIPSCO Industries, Inc., which changed its name to NiSource Inc. on April 14, 1999.

NiSource’s principal subsidiaries include NiSource Gas Distribution Group, Inc. (a holding company that owns Columbia of Kentucky, Columbia of Maryland, Columbia of Ohio, Columbia of Pennsylvania, and Columbia of Virginia), and NIPSCO Holdings I (a holding company that owns a controlling interest in NIPSCO, a gas and electric utility). NiSource derives substantially all of its revenues and earnings from the operating results of these rate-regulated businesses. In addition, NiSource will develop the generation resources it plans to use in serving data center customers through its subsidiary Generation Holdings I (a holding company that holds a controlling interest in GenCo).

Business Strategy

Our business strategy focuses on providing safe and reliable service through our core, rate-regulated, asset-based utilities, with the goal of adding value to all of our stakeholders. Our utilities continue to advance our core safety, infrastructure and environmental investment programs, supported by complementary regulatory and customer initiatives across the six states in which we operate. In 2025, we entered into the ADS Contract, a customized agreement under which NIPSCO will provide electric service to ADS by procuring power from GenCo, which will develop related generation assets, and we expect our data center operations to continue to grow.

Our goal is to develop strategies that (i) support long-term infrastructure investment and safety programs to better serve our customers, (ii) align our tariff structures with our cost structure, and (iii) drive value and enable growth in an evolving energy ecosystem. These strategies focus on improving safety and reliability, enhancing customer experience, pursuing regulatory and legislative initiatives to increase accessibility for customers currently not on our gas and electric service, ensuring customer affordability and reducing emissions while generating sustainable returns.

We remain committed to the advancement of our SMS for the safety of our customers, communities and employees. Our SMS is the established operating model within NiSource. NiSource continues to maintain its certification to the American Petroleum Institute Recommended Practice 1173, which serves as the guiding practice for our SMS. In 2025, NiSource successfully maintained its ISO 55001 Asset Management certifications through LRQA, a global leader in engineering and technology services. These certifications reaffirm our unwavering commitment to safety for our employees and partners, customers, and systems and highlight our continued dedication to operational excellence and the integrity of our SMS.

NiSource has two reportable segments: Columbia Operations and NIPSCO Operations. The remainder of our operations, which are not significant enough on a stand-alone basis to warrant treatment as an operating segment, consist of our centralized corporate activities and are primarily comprised of interest expense on holding company debt and unallocated corporate costs and activities, as well as new business development costs associated with GenCo. The following is a summary of the business for each reporting segment. Refer to Part II. Item 7, “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and Note 21, "Business Segment Information," in the Notes to Consolidated Financial Statements for additional information related to each segment.

Columbia Operations

Columbia Operations provides natural gas to approximately 2.4 million residential, commercial and industrial customers in Ohio, Pennsylvania, Virginia, Kentucky, and Maryland. We operate approximately 37,300 miles of distribution main pipeline plus the associated individual customer service lines and 310 miles of transmission main pipeline located in our service areas described above. Throughout our service areas we also have gate stations and other operations support facilities. See below for information on our owned storage facilities. There were no significant disruptions to our system or facilities during 2025.

NIS****OURCE **INC.**ITEM 1. BUSINESS

Competition. Due to open access and the deregulation of natural gas supplies, our LDC customers can purchase gas directly from producers and marketers in an open, competitive market. Certain of our subsidiaries are involved in programs that provide our residential and commercial customers the opportunity to purchase their natural gas requirements from third parties and use our subsidiaries for transportation services. As of December 31, 2025, 34.9% of our residential customers and 41.1% of our commercial customers participated in such programs.

We compete with (i) investor-owned, municipal, and cooperative electric utilities throughout our service areas, (ii) other regulated and unregulated natural gas intra and interstate pipelines and (iii) other alternate fuels, such as propane and fuel oil. We continue to be a well-positioned competitor in the energy markets in which we operate due to customer preference for natural gas.

Additionally, we are subject to seasonal fluctuations in sales. Revenues from our gas distribution operations are more significant during the heating season, which is from October through May. Please refer to Part II, Item 7, "Management's Discussion and Analysis of Financial Condition and Results of Operations - Results and Discussion of Operations - Columbia Operations," for additional information.

NIPSCO Operations

NIPSCO Operations includes the results of NIPSCO Holdings I and its majority-owned subsidiaries, including NIPSCO, which has fully regulated gas and electric operations in northern Indiana.

NIPSCO Gas

NIPSCO Gas distributes natural gas to approximately 0.9 million customers in northern Indiana. We operate approximately 18,100 miles of distribution main pipeline plus the associated individual customer service lines and 720 miles of transmission main pipeline located in our northern Indiana service areas. Throughout northern Indiana, we also have gate stations and other operations support facilities. See below for information on our owned storage facilities. There were no significant disruptions to our system or facilities during 2025.

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standards), interruption of service, accidents, or reputational harm, which could negatively impact our business, financial condition and results of operations. The nature of indirect supply chain, including a potential lack of control or certain visibility into sourcing by vendors, may also impact our ability to serve customers in a safe, reliable and cost-effective manner. These risks include the risk of operational failure, reputation damage, disruption due to new supply chain disruptions, exposure to significant commercial losses and fines and poorly positioned and distressed suppliers. If delayed deliveries and shortages or any other difficulties in the operations of these third-party suppliers and service providers, including their systems, were to occur, they could adversely affect our results of operations, or adversely affect our ability to work with regulators, unions, customers, or employees.

A cyber-attack or security breach on any of our or certain third-party technology systems, including but not limited to information systems, infrastructure, software and hardware, upon which we rely may adversely affect our ability to operate, could lead to a loss or misuse of confidential and proprietary information, or potential liability.

We are reliant on technology to run our business, which is dependent upon technology systems to process critical information necessary to conduct various elements of our business, including the generation, transmission and distribution of electricity; operation of our gas pipeline facilities; and the recording and reporting of commercial and financial transactions to regulators, investors and other stakeholders. In addition to general information and cybersecurity risks that all large corporations face (e.g., ransomware, malware, unauthorized access attempts, phishing attacks, malicious intent by insiders, third-party software vulnerabilities and inadvertent disclosure of sensitive information), the utility industry faces evolving and increasingly complex cybersecurity risks associated with protecting electric grid and natural gas infrastructure as well as sensitive and confidential customer and employee information. Deployment or adoption of new or emerging business technologies, including artificial intelligence, Internet of Things (IoT) devices, and cloud-based platforms, increased reliance on third-party vendors, cloud service providers and software supply chains, along with maintaining legacy technology, heightens our exposure to risks outside of our control and represents a large-scale opportunity for attacks on our information systems and confidential customer and employee information, as well as on the integrity of the electric grid and the natural gas infrastructure. Increasing large-scale corporate cyber-attacks in conjunction with more sophisticated threats continue to challenge utility companies. Additionally, international conflicts, as well as increased surveillance activity from global threat actors, has increased the likelihood of a cyber-attack or security breach on critical infrastructure systems.

Additionally, our information systems could experience sophisticated, cyber-attacks or security breaches by a variety of sources, including foreign sources, with the apparent aim to breach our cyber-defenses. While we have implemented and maintain a cybersecurity program designed to protect our information technology, operational technology, and data systems from such cyber-attacks or security breaches, our cybersecurity program does not prevent all breaches, cyber-attack or security breach incidents. We have experienced an increase in the number of attempts by external parties to access our networks or our company data without authorization. We have experienced, and expect to continue to experience, cybersecurity intrusions and attacks or security breaches to our information systems. To our knowledge, none of these intrusions or attacks have resulted in a material cybersecurity intrusion or data breach. The risk of a disruption or breach of our operational technology, or the compromise of the data processed in connection with our operations, through cybersecurity breach or ransomware attack has increased as attempted cyber-attacks or security breaches have advanced in sophistication and number around the world. Technological complexities combined with advanced cyber-attack or security breach techniques, lack of cybersecurity hygiene and human error can result in a cybersecurity incident, such as a ransomware attack. Supplier non-compliance with cybersecurity controls can also result in a cybersecurity incident. We are aware of vendor cybersecurity incidents that have impacted our business, although no such events have had a material impact. Cyber-attacks or security breaches can occur at any point in the supply chain or with any suppliers, and future supplier non-compliance with cybersecurity controls could result in material cybersecurity incidents. In addition, we use unmanned aircraft systems (UAS) or drones in our business operations. UASs are also being used for malicious activities and the cybersecurity risk in connection with operating UASs is increasing.

In addition, we collect and retain personally identifiable information of our customers and employees. Customers and employees expect that we will adequately protect their personal information.

A cybersecurity breach of our information systems or operational technology, or a cybersecurity breach of the information systems of our customers, suppliers or others with whom we do business, could, among other things, (i) adversely impact our ability to safely and reliably deliver electricity and natural gas to our customers through our generation, transmission and distribution systems and potentially negatively impact our compliance with certain mandatory reliability and gas flow standards, (ii) subject us to reputational and other harm or liabilities associated with theft or inappropriate release of certain types of information such as system operating information or information, personal or otherwise, relating to our customers or employees, (iii) impact our ability to manage our businesses, and/or (iv) subject us to legal and regulatory proceedings and

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ITEM 1A. RISK FACTORS

claims from third parties, in addition to remediation costs, any of which, in turn, could have a material adverse effect on our businesses, cash flows, financial condition and/or results of operations. Although we do maintain cybersecurity insurance, it is possible that such insurance will not adequately cover any losses or liabilities we may incur as a result of a cybersecurity incident.

Compliance with and changes in cybersecurity requirements have a cost and operational impact on our business, and failure to comply with such laws and regulations could adversely impact our reputation, results of operations, financial condition and/or cash flows.

The legal and regulatory environment surrounding cybersecurity and privacy is increasingly demanding. As cyber-attacks or security breaches are becoming more sophisticated, critical infrastructure assets, including pipelines and electric infrastructure, may be specifically targeted. In November 2024, the TSA issued a Notice of Proposed Rulemaking (NPRM) that would mandate cyber risk management and reporting requirements for the pipeline industry. Such directives or additional legal requirements may require expenditure of significant additional resources to respond to cyber-attacks or security breaches, to continue to modify or enhance protective measures, or to assess, investigate and remediate any critical infrastructure security vulnerabilities. Increased costs and the operational impacts of compliance and changes in cybersecurity requirements, including any failure to comply with government regulations or any failure in our cybersecurity protective measures may result in

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None.

We have implemented and maintain a comprehensive cybersecurity program that includes a variety of security controls and measures designed to identify, assess, and manage material cybersecurity risks. The program is a part of our enterprise risk management strategy. The enterprise risk team and the Risk Management Committee review material risks to any NiSource operating company based on perspectives from external experts, peer surveys, and the potential impact to our enterprise assets and strategic objectives.

Risk events are classified based on both the timing of impact and NiSource’s ability to preventatively mitigate the risk. For the cybersecurity risks that can be preventively mitigated, the enterprise risk team gathers quarterly updates on mitigation gap closure from risk owners. The Risk Management Committee reviews any mitigation gaps identified by risk owners and approves or rejects the pace of mitigation activities as a statement of risk tolerance and then directs that mitigation activities be included in budgets and the business plan as appropriate.

Our cybersecurity program includes the following key components:

Risk assessment. We regularly assess our cybersecurity risks to identify and prioritize the most significant threats. The risk assessment process considers a variety of factors, including those specific to the utility/energy industry, the types of data we collect and store, and the threats posed by known vulnerabilities. We engage third parties to perform independent assessments of our cybersecurity program, provide intelligence about the threat environment, and to provide operational assistance in managing the program. Annually, a third-party independent assessment is performed to evaluate our cybersecurity maturity against a framework of cybersecurity controls. We also perform bi-annual penetration testing and social engineering assessments performed by a third-party.

Third-party risk management. We perform cyber assessments periodically on all third-party vendors and service providers with whom we share data, rely on for critical business functions, or provide access to our network or systems. Our Supply Chain function works with the Legal and Cyber functions to periodically update cybersecurity contractual provisions in its vendor agreements, with deviations from such provisions requiring approval from the Legal and Cyber functions. Our Supplier Code of Business Conduct requires, among other things, that suppliers ensure safe and secure use of information assets, comply with applicable law relating to personal information, and adhering to standards relative to the use and protection of our information, including that of our employees, customers, vendors and other stakeholders. In addition, all vendors and contractors that have access and/or connectivity to our environment must complete cybersecurity training annually.

Security controls. We have implemented a variety of security controls to mitigate cybersecurity risks. These controls include technical controls, such as firewalls and intrusion detection systems, as well as administrative controls, such as employee training and security awareness programs. To ensure cybersecurity controls, our operational technology within the electric business adheres to the NERC CIP. Within the natural gas business, cybersecurity controls are managed and monitored based on the TSA Security Directives.

Incident response. We have a comprehensive incident response plan in place to respond to cybersecurity incidents. The plan includes steps for detection, analysis, containment, eradication, and recovery from incidents, as well as steps for notifying affected individuals and regulators.

The Audit Committee of our Board has responsibility for oversight of the cybersecurity program and risks from cybersecurity threats. The Audit Committee regularly reviews our cybersecurity posture. The CISO briefs the Audit Committee on cybersecurity risks and risk mitigation initiatives and actions. In addition, the Board remains informed of key and emerging cybersecurity risks and receives updates by the Audit Committee after each of its regularly scheduled meetings.

At the management level, the CISO leads the cybersecurity program and is responsible for assessing and managing cybersecurity risks. Our CISO has expertise and experience in cybersecurity derived from over 15 years of cyber related work experience and possesses several certifications including CISSP, CRISC, and CISA. The CISO is supported by the NiSource Enterprise Security team which performs the cybersecurity function and engages directly on the prevention, detection, mitigation, and remediation of cybersecurity incidents.

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As of the date of filing this Annual Report on Form 10-K, we are not aware of any material cybersecurity incidents during the past year. We monitor the increasing sophistication of cybersecurity threats and continue to allocate resources to enhance our cybersecurity program to protect its information systems and assets. No cybersecurity program is effective to identify and mitigate all threats and we cannot guarantee that we will be able to prevent all cybersecurity incidents. Such an incident could interrupt our normal operations and require us to incur significant costs to remediate any such incident and could have a material impact on our businesses, operations and financial condition. For more information regarding the risks associated with cybersecurity, refer to “Item 1A. Risk Factors” of this Annual Report on Form 10-K.

Discussed below are the principal properties held by us and our subsidiaries as of December 31, 2025.

Columbia Operations

Refer to Item 1, "Business - Columbia Operations," of this report for further information on Columbia Operations properties.

NIPSCO Operations

Refer to Item 1, "Business - NIPSCO Operations," of this report for further information on NIPSCO Operations properties.

Corporate and Other Operations

We own the Southlake Complex, our 325,000 square foot headquarters building located in Merrillville, Indiana.

Character of Ownership

Our principal properties and our subsidiaries' principal properties are free from encumbrances, subject to minor exceptions, none of which are of such a nature as to impair substantially the usefulness of such properties. Many of our subsidiary offices in the various communities we serve are occupied under leases. All properties are subject to routine liens for taxes, assessments and undetermined charges (if any) incidental to construction. It is our practice to regularly pay such amounts, as and when due, unless contested in good faith. In general, the electric lines, gas pipelines and related facilities are located on land not owned by us or our subsidiaries, but are covered by necessary consents of various governmental authorities or by appropriate rights obtained from owners of private property. We do not, however, generally have specific easements from the owners of the property adjacent to public highways over, upon or under which our electric lines and gas distribution pipelines are located. At the time each of the principal properties was purchased, a title search was made. In general, no examination of titles as to rights-of-way for electric lines, gas pipelines or related facilities was made, other than examination, in certain cases, to verify the grantors’ ownership and the lien status thereof.

For a description of our legal proceedings, see Note 19, "Other Commitments and Contingencies - C. Legal Proceedings," in the Notes to Consolidated Financial Statements.

Not applicable.

Table of ContentsNIS****OURCE INC.

PART II

NiSource’s common stock is listed and traded on the New York Stock Exchange under the symbol "NI."

Holders of shares of NiSource’s common stock are entitled to receive dividends if and when declared by the Board out of funds legally available. There is no preferred stock outstanding as of December 31, 2025. The policy of the Board has been to declare cash dividends on a quarterly basis payable on or about the 20th day of February, May, August, and November. At its January 22, 2026 meeting, the Board declared a quarterly common dividend of $0.300 per share, payable on February 20, 2026 to holders of record on February 3, 2026.

Although the Board currently intends to continue the payment of regular quarterly cash dividends on common shares, the timing and amount of future dividends will depend on the earnings of NiSource’s subsidiaries, their financial condition, cash requirements, regulatory restrictions, any restrictions in financing agreements and other factors deemed relevant by the Board. There can be no assurance that NiSource will continue to pay such dividends or the amount of such dividends.

As of February 4, 2026 NiSource had 14,211 common stockholders of record and 478,533,171 shares outstanding.

The graph below compares the cumulative total shareholder return of NiSource’s common stock for the period commencing December 31, 2020 and ending December 31, 2025 with the cumulative total return for the same period of the S&P 500 and the Dow Jones Utility indices.

The foregoing performance graph is being furnished as part of this Annual Report on Form 10-K solely in accordance with the requirement under Rule 14a-3(b)(9) to furnish stockholders with such information, and therefore, shall not be deemed to be filed or incorporated by reference into any filings by NiSource under the Securities Act or the Exchange Act.

The total shareholder return for NiSource common stock and the two indices is calculated from an assumed initial investment of $100 and assumes dividend reinvestment.

Purchases of Equity Securities by Issuer and Affiliated Purchasers. For the three months ended December 31, 2025, no equity securities that are registered by NiSource Inc. pursuant to Section 12 of the Securities Exchange Act of 1934 were purchased by or on behalf of us or any of our affiliated purchasers.

Not applicable.

NIS****OURCE INC. ITEM 7. MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

EXECUTIVE SUMMARY

This Management's Discussion and Analysis of Financial Condition and Results of Operations ("Management's Discussion") includes management’s analysis of past financial results and certain potential factors that may affect future results, potential future risks and approaches that may be used to manage those risks. See "Note regarding forward-looking statements" and Item 1A, "Risk Factors" at the beginning of this report for a list of factors that may cause results to differ materially. Refer to the "Business" section under Part I, Item 1 of this Annual Report on Form 10-K and Note 21, "Business Segment Information," in the Notes to Consolidated Financial Statements for further discussion of our regulated utility business segments.

This Management's Discussion is designed to provide an understanding of our operations and financial performance and should be read in conjunction with our Consolidated Financial Statements and related Notes to Consolidated Financial Statements in this Annual Report on Form 10-K.

We are an energy holding company under the Public Utility Holding Company Act of 2005 whose primary subsidiaries are fully regulated natural gas and electric utility companies serving customers in six states. We generate substantially all of our operating income through these rate-regulated businesses, which are summarized for financial reporting purposes into two primary reportable segments: Columbia Operations and NIPSCO Operations.

Our vision is to be a premier, innovative and trusted energy partner. We exist to deliver safe, reliable energy that drives value to our customers. In order to achieve this goal, we seek to develop strategies that benefit all stakeholders as we (i) support long-term infrastructure investment and safety programs to better serve our customers, (ii) align our tariff structures and regulatory programs with our cost structure, and (iii) create value and enable growth in an evolving energy ecosystem. These strategies focus on improving safety and reliability, enhancing customer experience, pursuing regulatory and legislative initiatives to increase accessibility for customers currently not on our gas and electric service, ensuring customer value and reducing emissions while generating sustainable returns. The safety of our customers, communities and employees remains our focus. Serving as a guiding practice for our SMS, NiSource is certified in conformance to the American Petroleum Institute Recommended Practice 1173, which is the foundation to our journey towards operational excellence.

2025 Overview:

In 2025, we continued to make significant progress on the remaining portfolio of projects that will enable our electric generation transition, including placing two solar projects and one solar and battery project into service. We advanced our Data Center strategy significantly by creating our GenCo affiliate, whose goal is to build capacity to serve large load customers. We also executed the ADS Contract and related EPC contracts discussed below. During the year, we received orders for four rate cases: Columbia of Maryland, Columbia of Pennsylvania, Columbia of Virginia, and NIPSCO Electric. Between our Columbia and NIPSCO Operating Segments, we added 24,000 customers. We also invested $1.6 billion in infrastructure modernization to enhance safe, reliable service, including replacement of 256 miles of distribution main and service lines, 45 miles of underground cable and 1,656 electric poles. We concluded the second and third phases of a WAM ERP program, covering all gas distribution operations across our operating territories and our generation assets, to optimize the scheduling, dispatch, and execution of our field operations.

ADS Contract and Data Center Strategy:

ADS Contract

In September 2025, NIPSCO entered into an agreement with ADS, a wholly-owned subsidiary of Amazon.com, Inc., under which NIPSCO will provide electricity to ADS' data centers. Under the ADS Contract, which is pending IURC approval, NIPSCO will provide electric service to ADS pursuant to a capacity commitment beginning in 2027 and increasing annually to

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2,400 MW by the end of 2032 and will construct up to 3,000 MW of dispatchable generation to provide such electric service. The ADS Contract’s initial term ends 15 years after the initial energization of ADS’ initial data center. Starting January 2027, ADS will regularly pay NIPSCO a fixed capacity charge and certain pass-through charges. Amazon.com, Inc. a publicly traded, investment-grade parent company has guaranteed ADS’ payment obligations. These charges are structured to provide us with a return of our invested capital over the fifteen-year initial term. In addition, the ADS Contract contains provisions for adjustment of the charges designed to provide us with an unlevered internal rate of return on our invested capital over the initial term within a defined range, which we expect over the life of the ADS contract to result in an overall realized return greater than that of NIPSCO’s current electric operations, driven by execution and financing. Our realized return may be impacted by factors such as construction costs, operating performance, financing costs and other variables. NIPSCO will also propose to the IURC a mechanism to pass savings back to retail customers for use of the existing system which is expected to begin in 2027. Refer to Part I, Item 1A, “Risk Factors” for a discussion of certain of these factors and other risks relating to the ADS Contract.

In order to meet demand under the ADS Contract, NIPSCO has entered into a PPA with GenCo, which is pending IURC approval and contains terms and provisions substantially similar to the ADS Contract, such that economic benefits (except savings that are expected to be passed to retail customers as described above) and obligations of the ADS Contract as they relate to the Generation Assets (as defined below) are expected to be borne by GenCo and NiSource, as GenCo’s ultimate parent company, rather than NIPSCO.

GenCo plans to construct 400 MW of new battery storage and a new power generation facility consisting of two 1,300 MW CCGTs, which are expected to reach commercial operation between 2028 and 2032 (such assets, collectively, the “Generation Assets”). NIPSCO currently has a proceeding before the IURC to approve the generation facilities required to be built for ADS. GenCo has entered into engineering, procurement and construction contracts (the “EPC Contracts”), and certain equipment supply contracts, including a contract to acquire turbines, with respect to the construction of the Generation Assets. The aggregate cost of the Generation Assets, together with the cost to develop related transmission infrastructure (collectively, the “Contract Assets”), is currently estimated to be approximately $7 billion. The EPC Contracts provide certain protections against cost overruns, and any excess costs with respect to the EPC Contracts beyond those protections, or arising apart from the EPC Contracts are, unless otherwise agreed by the parties, shared by ADS and NIPSCO (for transmission) and GenCo (for generation). If the Contract Assets are delivered into service late or do not achieve certain performance-related milestones, ADS is entitled to liquidated damages, subject to a cap and offset against the regular charges paid by ADS.

Either party may terminate the ADS Contract upon certain defaults or failure to obtain necessary related approvals from the IURC and FERC. ADS may terminate the ADS Contract for convenience following certain notice periods and also has a one-time option (exercisable no later than March 31, 2029) to halve the committed capacity under the ADS Contract to 1,200 MW commencing January 31, 2032. If ADS terminates for convenience, exercises its reduction option or defaults, NIPSCO or its affiliates will be reimbursed for investment costs, subject to agreed caps based on cost estimates by year as of signing. NIPSCO’s aggregate liability, including liquidated damages, is subject to a cap.

NIPSCO’s and GenCo’s operations under the ADS Contract will be regulated by the IURC in a different way from the regulatory mechanisms applicable to NIPSCO’s historical operations. The terms of the ADS Contract were determined by commercial negotiation with ADS. These terms include the charges we receive from ADS and provisions that may result in adjustments to such charges, including those relating to certain liquidated damages that we may owe ADS in the event of construction delays or capacity shortfalls, the parties’ responsibility to share cost overruns, certain changes in law and force majeure events. The IURC will not determine the commercial terms of the ADS Contract; however, the IURC will maintain oversight under the ADS Contract to ensure NIPSCO provides reliable service to ADS at just and reasonable rates. In order to recover our investment costs and earn our return under the ADS Contract, our subsidiaries must efficiently perform their own obligations and must look to ADS (or its parent guarantor) to perform its obligations, rather than the IURC making use of its traditional rate-making process. In addition, under the ADS Contract, NIPSCO has direct contractual obligations to ADS to, among other things, construct the Contract Assets and deliver committed electric capacity in fixed amounts by certain dates.

The terms of any future data center contracts we enter into may differ from the terms of the ADS Contract. For example, customer demand may not be served through designated assets and may contemplate that capacity will be procured via PPAs with third parties. However, the terms of any future data center contracts (including the charges we receive from customers and any potential adjustments to such charges) will inform our ability to recover our investments and earn a return. Similar to the ADS Contract, any additional data center contracts will be subject to IURC approval and oversight authority, but the IURC will not determine the commercial terms.

Data Center Strategy

We continue to experience strong demand from potential data center customers in our northern Indiana service territory and are engaged in negotiations with potential counterparties. Through certain of our subsidiaries, we have entered into certain

NIS****OURCE INC. ITEM 7. MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS (continued)

construction and equipment supply contracts in relation to additional generation and transmission assets that may be used to serve potential future data center customers. As we continue to evaluate our potential data center opportunities, we will continue to focus on the community, financial, operational and regulatory factors that must be managed effectively in order to succeed with our data center strategy. We believe data center development can enhance our local tax base, diversify the employment base across the state of Indiana, and provide greater value to existing customers and shareholders. We continually evaluate ways to effectively manage the potential power demand, generation sources, and transmission capabilities to meet potential further load growth from additional data center customers, while at the same time focusing on our environmental goals.

In order to perform under any further data center contracts, we expect that we would need to develop additional generation and transmission assets, which may be significant, and obtain additional financing in connection with such development. For these and other reasons, our ability to successfully execute our data center strategy is subject to a number of risks and uncertainties. Refer to Part I, Item 1A, “Risk Factors” for a discussion of certain risks relating to our data center strategy.

Energy Transition:

We continue to advance our energy transition strategy, primarily through the continuation and enhancement of existing programs, such as implementing our plan to retire and replace remaining coal-fired electric generation by 2028 with a balanced m

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Quantitative and Qualitative Disclosures about Market Risk are reported in Item 7, “Management’s Discussion and Analysis of Financial Condition and Results of Operations – Market Risk Disclosures.”

NIS****OURCE INC. ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

NIS****OURCE **INC.**ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA (continued)

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the shareholders and the Board of Directors of NiSource Inc.

Opinion on the Financial Statements

We have audited the accompanying consolidated balance sheets of NiSource Inc. and subsidiaries (the "Company") as of December 31, 2025 and 2024, the related consolidated statements of income, comprehensive income, stockholders' equity, and cash flows, for each of the three years in the period ended December 31, 2025, and the related notes and the schedule listed in the Index at Item 15 (collectively referred to as the "financial statements"). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Company as of December 31, 2025 and 2024, and the results of its operations and its cash flows for each of the three years in the period ended December 31, 2025, in conformity with accounting principles generally accepted in the United States of America.

We have also audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the Company's internal control over financial reporting as of December 31, 2025, based on criteria established in Internal Control — Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission and our report dated February 11, 2026, expressed an unqualified opinion on the Company's internal control over financial reporting.

Basis for Opinion

These financial statements are the responsibility of the Company's management. Our responsibility is to express an opinion on the Company's financial statements based on our audits. We are a public accounting firm registered with the PCAOB and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud. Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. We believe that our audits provide a reasonable basis for our opinion.

Critical Audit Matter

The critical audit matter communicated below is a matter arising from the current-period audit of the financial statements that was communicated or required to be communicated to the audit committee and that (1) relates to accounts or disclosures that are material to the financial statements and (2) involved our especially challenging, subjective, or complex judgments. The communication of critical audit matters does not alter in any way our opinion on the financial statements, taken as a whole, and we are not, by communicating the critical audit matter below, providing a separate opinion on the critical audit matter or on the accounts or disclosures to which it relates.

Regulatory Matters - Impact of Rate Regulation on the Financial Statements – Refer to Notes 1, 9, and 12 to the financial statements

Critical Audit Matter Description

The Company’s primary subsidiaries are fully regulated natural gas and electric utility companies serving customers in six states. These rate-regulated subsidiaries account for and report assets and liabilities consistent with the economic effect of the manner in which regulators establish rates, if the rates established are designed to recover the costs of providing the regulated service and it is probable that such rates can be charged to and collected from customers. Certain expenses and credits subject to utility regulation or rate determination normally reflected in income are deferred on the consolidated balance sheets and are later recognized in income as the related amounts are included in customer rates and recovered from or refunded to customers.

NIS****OURCE **INC.**ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA (continued)

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

The Company’s subsidiaries’ rates are determined and approved in regulatory proceedings based on an analysis of the subsidiaries’ costs to provide utility service and a return on, and recovery of, the subsidiaries’ investment in the utility business. Regulatory decisions can have an impact on the recovery of costs, the rate of return earned on investment, and the timing and amount of assets to be recovered by rates. The respective commission’s regulation of rates is premised on the full recovery of prudently incurred costs and a reasonable rate of return on invested capital. Decisions to be made by the commission in the future will impact the accounting for regulated operations, including decisions about the amount of allowable costs and return on invested capital included in rates and any refunds that may be required. While the Company has indicated it expects to recover costs from customers through regulated rates, there is a risk that the commission will not approve: (1) full recovery of the costs of providing utility service, or (2) full recovery of all amounts invested in the utility business and a reasonable return on that investment.

We identified the impact of rate regulation, specifically certain regulatory assets and liabilities at the Company’s Northern Indiana Public Service Company LLC and Columbia Gas of Ohio, Inc. subsidiaries, as a critical audit matter due to the significant judgments made by management to support its assertions about certain account balances and the significant degree of subjectivity involved in assessing the likelihood of recovery of incurred costs in current or future rates due in part to uncertainty related to future decisions by the rate regulators. This required specialized knowledge of accounting for rate regulation and the rate setting process due to its inherent complexities and a significant degree of auditor judgment when performing audit procedures to evaluate the reasonableness of management’s conclusions.

How the Critical Audit Matter Was Addressed in the Audit

Our audit procedures related to the application of specialized rules to account for the effects of cost-based rate regulation related to the uncertainty of future decisions by the rate regulators, specifically the Indiana Utility Regulatory Commission (IURC) and the Public Utilities Commission of Ohio (PUCO), included the following, among others:

• We tested the effectiveness of management’s controls over (1) the evaluation of the likelihood of (a) the recovery of costs deferred as regulatory assets in future periods, and (b) regulatory developments that may affect the likelihood of recovering costs in future rates or of a future reduction in rates; and (2) the evaluation of Hypothetical Liquidation Book Value (HLBV) accounting for the company’s renewable facility joint ventures and its impact on the Company’s regulatory liability.

• We evaluated Northern Indiana Public Service Company LLC and Columbia Gas of Ohio, Inc.’s disclosures related to the financial statement impacts of rate regulation.

• We read relevant regulatory orders issued by the IURC and PUCO, including regulatory statutes, interpretations, procedural memorandums, filings made by interveners, and other publicly available information to assess the likelihood of recovery in future rates or a future reduction in rates based on precedents of the commissions’ treatment of similar costs under similar circumstances. We evaluated this external information and compared to management’s recorded regulatory asset and liability balances for completeness, including the implementation of a new base rate order at Northern Indiana Public Service Company LLC’s electric business.

• We inspected minutes of the boards of directors for discussions of changes in legal, regulatory, or business factors which could impact management’s conclusions with respect to the financial statement impacts of rate regulation.

• For the Northern Indiana Public Service Company LLC's electric base rate case that was approved in 2025, we inspected the order for any evidence that might contradict management’s assertions related to recoverability of recorded assets.

• We inquired of management about property, plant, and equipment that may be abandoned with an emphasis on the generation strategy related to Northern Indiana Public Service Company LLC’s R.M. Schahfer and Michigan City Generating Stations. We inspected minutes of the board of directors, regulatory orders, the Department of Energy’s

NIS****OURCE **INC.**ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA (continued)

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

Order Under Federal Power Act Section 202(c), and other filings with the IURC to identify evidence that may contradict management’s assertion regarding probability of abandonment.

• We read the relevant regulatory orders issued by the IURC for the Company’s renewable energy investments held within joint ventures. We evaluated the appropriateness of recognizing a regulatory liability for timing differences between the profit allocated under the HLBV accounting method and the allowed earnings included in rates for these joint ventures. We also evaluated the appropriateness of the offset to the regulatory liability recorded in depreciation expense.

/s/ DELOITTE & TOUCHE LLP

Columbus, Ohio

February 11, 2026

We have served as the Company's auditor since 2002.

NIS****OURCE INC. ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA (continued)

STATEMENTS OF CONSOLIDATED INCOME

The accompanying Notes to Consolidated Financial Statements are an integral part of these statements.

NIS****OURCE INC.

ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA (continued)

STATEMENTS OF CONSOLIDATED COMPREHENSIVE INCOME

(1) Net unrealized gain on available-for-sale securities, net of $1.1 million tax expense, $0.9 million tax expense and $1.0 million tax expense in 2025, 2024 and 2023, respectively.

(2) Net unrealized loss on derivatives qualifying as cash flow hedges, net of $0.1 million tax benefit, $0.1 million tax benefit and $0.1 million tax benefit in 2025, 2024 and 2023, respectively.

(3) Unrecognized pension and OPEB benefit (costs), net of $4.4 million tax expense, $0.3 million tax expense and $0.1 million tax benefit in 2025, 2024 and 2023, respectively.

The accompanying Notes to Consolidated Financial Statements are an integral part of these statements.

NIS****OURCE INC.

ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA (continued)

CONSOLIDATED BALANCE SHEETS

(1)Includes $1,312.7 million and $1,323.8 million in 2025 and 2024, respectively, of net property, plant and equipment assets, $90.1 million and $65.0 million in 2025 and 2024, respectively, of current assets of consolidated VIEs that may be used only to settle obligations of the consolidated VIEs. Refer to Note 4, "Noncontrolling Interests," for additional information.

(2)Includes $305.4 million in 2025 of advanced deposits of project costs of consolidated VIEs that may be used only to settle obligations of the consolidated VIEs. Refer to Note 4, "Noncontrolling Interests," for additional information.

The accompanying Notes to Consolidated Financial Statements are an integral part of these statements.

NIS****OURCE INC.

ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA (continued)

CONSOLIDATED BALANCE SHEETS

(1)Includes $56.9 million and $53.7 million in 2025 and 2024, respectively, of current liabilities, $55.7 million and $58.3 million in 2025 and 2024, respectively, of other liabilities, and finance leases of $40.1 million and $40.4 million in 2025 and 2024, respectively, of consolidated VIEs that creditors do not have recourse to our general credit. Refer to Note 4, "Noncontrolling Interests," for additional information.

The accompanying Notes to Consolidated Financial Statements are an integral part of these statements.

NIS****OURCE INC.

ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA (continued)

STATEMENTS OF CONSOLIDATED CASH FLOWS

The accompanying Notes to Consolidated Financial Statements are an integral part of these statements.

NIS****OURCE INC.

STATEMENTS OF CONSOLIDATED STOCKHOLDERS' EQUITY