Anterix Inc.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

(Mark One)

For the fiscal year ended March 31, 2026

OR

For the transition period from to

Commission File Number: 001-36827

(Exact name of registrant as specified in its charter)

(973)771-0300

(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 Rule 405 of the Securities Act. ☐ Yes ☒No

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

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 ☐ 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 ☐ 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 definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

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 registrant 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

The aggregate market value of the registrant’s voting common and non-voting stock held by non-affiliates of the registrant based on the closing stock price of its common stock on the Nasdaq Capital Market on September 30, 2025 (the last business day of its most recently completed second fiscal quarter) was $241,938,984. For purposes of this computation only, all executive officers, directors and 10% or greater stockholders have been deemed affiliates of the registrant.

As of June 19, 2026,19,498,473 shares of the registrant’s common stock were outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission pursuant to Regulation 14A in connection with the registrant’s 2026 Annual Meeting of Stockholders, which will be filed subsequent to the date hereof, are incorporated by reference into Part III of this Form 10-K where indicated. Such definitive proxy statement will be filed with the Securities and Exchange Commission no later than 120 days following the end of the registrant’s fiscal year ended March 31, 2026.

FORM 10-K

For the fiscal year ended March 31, 2026

TABLE OF CONTENTS

Glossary of Selected Terms

Unless otherwise noted or indicated by context, the following selected terms used in this Annual Report on Form 10-K have the following meanings:

240 Channels: Equals 6 MHz of 900 MHz spectrum whether the individual 25 kHz channels are scattered throughout the 5 x 5 or 10 MHz 900 MHz band or are contained within the contiguous 3 x 3 or 6 MHz broadband segment.

3 x 3 or 6 MHz: The broadband segment of the 900 MHz band (897.5 - 900.5 / 936.5 - 939.5 MHz) is authorized for a total of 6 MHz of spectrum, with 3 MHz designated for uplink transmissions and 3 MHz for downlink transmissions.

5 x 5 or 10 MHz: The narrowband and broadband segment of the 900 MHz band (896 - 901 / 935 - 940 MHz) are authorized for a total of 10 MHz of spectrum, with 5 MHz designated for uplink transmissions and 5 MHz for downlink transmissions.

3GPP: The 3rd Generation Partnership Project is the standards organization that develops protocols for mobile telecommunications, such as Radio Access Networks, Services and Systems Aspects, and Core Network and Terminals.

4G: 4th generation of radio system architecture.

5G:5th generation of radio system architecture.

600 MHz Auction: The Federal Communications Commission’s (the “FCC”) 2016 “incentive auction” in which licensees of television broadcast channels were incentivized to relinquish their spectrum for defined payments so the spectrum could be repurposed for licensed wireless services.

900 MHz: The 900 MHz band frequency ranges between 896 - 901 / 935 - 940 MHz.

900 MHz Broadband Spectrum or 900 MHz Broadband Segment: The 900 MHz band authorized for broadband (897.5 - 900.5 / 936.5 - 939.5 MHz).

Anti-Windfall Payment: A payment to the U.S. Treasury from a 900 MHz broadband applicant, if the applicant relinquishes less than 6 MHz (or 240 channels) of spectrum for any full or fractional MHz less than 6 MHz for 3 x 3 applicants or less than 10 MHz (or 399 channels) of spectrum for any full or fractional MHz less than 10 MHz for 5 x 5 applicants. The payment is based on the 600 MHz Auction prices for the Partial Economic Area in which the county applied for by the broadband applicant is included.

Band 106 or n106: The broadband segment of the 900 MHz band (896 - 901 / 935 - 940 MHz), designated as LTE Band 106 (B106) or n106 (5G designation), is seen as critical for utilities to modernize grid communication.

Band 8: LTE Band 8, also known as the 900 MHz band, is a frequency band used for both 2G GSM and 4G LTE mobile communications.

B/ILT: Systems operated by, or spectrum licensed for, private land mobile use by business users.

Complex System: As defined in the 2020 Report and Order, a Covered Incumbent’s system that consisted of 45 or more functionally integrated sites as of May 13, 2020.

Covered Incumbent: Any 900 MHz site-based licensee in the broadband segment that is required under section 90.621(b) to be protected by a broadband licensee with a base station at any location within the county, or any 900 MHz geographic-based Specialized Mobile Radio (“SMR”) licensee in the 3 x 3 MHz broadband segment or 5 x 5 900 MHz frequency range whose license area completely or partially overlaps the county.

Eligibility Certification: A document submitted to the FCC as part of the broadband application that lists the licenses the applicant holds in the 900 MHz band to demonstrate that it holds the licenses for more than 50% of the total licensed 900 MHz spectrum for the relevant county, including credit for spectrum contained in a contract to acquire any covered incumbents filed on or after March 14, 2019 (i.e., the 50% Licensed Spectrum Test).

FCC: The Federal Communications Commission, an independent U.S. government agency overseen by Congress, is the United States’ primary authority for communications law, regulation and technological innovation. The FCC regulates interstate and international communications by radio, television, wire, satellite and cable in all 50 states, the District of Columbia and U.S. territories.

Integrated Platform: A cloud-based 4G/5G core, enabling greater resilience and enhanced services between participating networks, including mutual aid, cybersecurity, shared infrastructure, and integration of distributed energy sources.

Licensed Channel: Any of the 399 12.5 kHz narrowband 900 MHz channels for which there is a current, active FCC license to an existing entity. Not all 900 MHz channels are currently licensed as some channels are held in the FCC inventory. The FCC will provide credit to the broadband applicant for incumbent channels cancelled pursuant to a contract with the broadband applicant.

Mandatory Retuning: A process by which a 900 MHz broadband licensee can mandatorily relocate a Covered Incumbent to channels outside of the 900 MHz Broadband Segment if the replacement channels provide comparable facilities to the Covered Incumbent’s existing system and the broadband licensee pays all reasonable retuning costs.

MTA: Major Trading Area; service areas based on the Rand McNally 1992 Commercial Atlas & Marketing Guide, which defines the original geography of the FCC auctioned 900 MHz SMR licenses.

Narrowband Channel: A 900 MHz 25 kHz bandwidth channel.

PLTE: A private long-term evolution wireless network that is deployed and controlled specifically for the benefit of one organization. Only users authorized by that organization have access to the network. The organization determines coverage, network performance, access and priority, the appropriate service level required for operations, specific cyber and physical security specifications and policies required for the network.

Retuning: Modifying an incumbent’s narrowband system to operate on channels outside the 900 MHZ Broadband Segment established by the Report and Order.

Swapping: Exchanging narrowband channels outside the 900 MHz Broadband Segment for the broadband segment channels held by a Covered Incumbent.

Transition Plan: A document filed as part of the broadband application that demonstrates that the broadband license applicant holds, or has agreements to acquire, cancel, relocate or protect, at least 90% of the licensed channels in the 900 MHz Broadband Segment of Covered Incumbents in or within 70 miles of the county (i.e., the 90% Broadband Segment Test). The 2026 Report and Order require the broadband application to demonstrate that the broadband license applicant holds, or has agreements to acquire, cancel, relocate or protect, 100% of the licensed channels in the 900 MHz Broadband Segment of Covered Incumbents in or within 70 miles of the county for a 5 x 5 MHz Broadband License.

CAUTIONARY STATEMENT CONCERNING FORWARD-LOOKING STATEMENTS

Various statements contained in this Annual Report on Form 10-K (the “Annual Report”), including those that express a belief, expectation, or intention, as well as those that are not statements of historical fact, are forward-looking statements. Our forward-looking statements are generally, but not always, accompanied by words such as, but not limited to, “aim,” “anticipate,” “believe,” “can,” “continue,” “could,” “estimate,” “expect,” “goal,” “intend,” “may,” “might,” “ongoing,” “plan,” “possible,” “potential,” “predict,” “project,” “seek,” “should,” “strategy,” “target,” “will,” “would” and similar expressions or phrases, or the negative of those expressions or phrases, or other words that convey the uncertainty of future events or outcomes, which are intended to identify forward-looking statements, although not all forward-looking statements contain these words. We have based these forward-looking statements on our current expectations, guidance and projections and related assumptions about future events and financial trends. While our management considers these expectations, guidance, projections and assumptions to be reasonable, they are inherently subject to significant business, economic, competitive, regulatory and other risks, contingencies and uncertainties, most of which are difficult to predict and many of which are beyond our control. There can be no assurance that actual developments will be as we anticipate. Actual results may differ materially from those expressed or implied in these statements as a result of significant risks and uncertainties, including, but not limited to:

•our ability to successfully commercialize our spectrum assets to our targeted utility and critical infrastructure customers on a timely basis, and on commercially favorable terms, including our ability to monetize our spectrum on financial terms consistent with our business plan and assumptions;

•our ability to satisfy our obligations, including the delivery of cleared spectrum and broadband licenses, and the other contingencies required by our commercial agreements with our customers on a timely basis and on commercially reasonable terms;

•our ability to develop, market and sell and deliver new products and services offerings, in addition to our spectrum assets, to our targeted and critical infrastructure customers;

•our ability to successfully compete against third parties who offer spectrum and communication technologies, products and solutions to our targeted customers;

•our ability to successfully manage our business in light of macroeconomic pressures, including but not limited to inflation, regulatory and policy changes, and geopolitical matters;

•our ability to correctly estimate our cash receipts, revenues and operating expenses and our future financial needs;

•our ability to achieve our operating and financial projections and guidance;

•our ability to support our future operations and business plans and return capital to our stockholders through our share repurchase program with our existing cash resources and the proceeds we generate from our commercial operations without raising additional capital through the issuance of stock or debt securities;

•our ability to qualify for and obtain broadband licenses in a timely manner or at all from the FCC in accordance with the requirements of the Report and Order approved by the FCC on May 13, 2020 (the “2020 Report and Order”) and the Report and Order approved by the FCC on February 18, 2026 (the “2026 Report and Order”, collectively, the “Report and Order”);

•our ability to retune, protect, cancel or acquire Covered Incumbent narrowband channels, including Complex Systems, in a timely manner and on commercially reasonable terms, or at all;

•our expectations with respect to our efforts to encourage federal and state agencies and commissions supporting the deployment of broadband networks and services by our targeted customers;

•our ability to maintain any narrowband and broadband licenses that we own, acquire and/or obtain;

•our ability to respond to changes in government regulations or actions and the impact of such changes on our business prospects, liquidity and results of operations, including any changes by the FCC to the Report and Order or to the FCC rules and regulations governing the 900 MHz band;

•the expected timing, the amount of repurchases and the related impact to our common stock relating to our share repurchase program;

•our expectations regarding our ability to maintain an effective system of internal controls; and

•our statements regarding the factors that may impact our financial results and stock price.

These and other important factors, including those discussed under “Item 1. Business,” “Item 1A. Risk Factors” and “Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations” within this Annual Report may cause our actual results, performance or achievements to differ materially from any future results, performance or achievements expressed or implied by these forward-looking statements. Therefore, you are cautioned not to place undue reliance on such statements. Further, any forward-looking statement speaks only as of the date on which it is made, and except to the extent required by applicable law, we undertake no obligation to update any forward-looking statement to reflect events or circumstances after the date on which the statement is made or to reflect the occurrence of unanticipated events, whether as a result of new information, future events or otherwise.

Page 1

SUMMARY OF RISK FACTORS

We have prepared the following summary of the principal risks to our business and the risks associated with ownership of our common stock. This summary does not address all of the risks that we face. We encourage you to carefully review the full risk factors contained in this Annual Report in their entirety for additional information regarding the material factors that make an investment in our securities speculative or risky. These risks and uncertainties include, but are not limited to, the following:

•we may not be successful in commercializing our spectrum assets to our targeted utility and critical infrastructure customers on a timely basis, and on commercially favorable terms, including our ability to monetize our spectrum on financial terms consistent with our business plan and assumptions;

•our commercial agreements with our customers are subject to contingencies and obligations, including the delivery of cleared spectrum and broadband licenses on a timely basis, and as a result, there is no assurance that we will receive payments from such customers in the amounts and on the timeline we currently expect, or that any payments we have received to date will not be subject to repayment, or that we will not be subject to contract claims, including rights of termination;

•we may not be successful in developing, marketing, selling and delivering new products and services offerings to our targeted utility and critical infrastructure customers;

•we may not be successful in competing against other spectrum holders who offer spectrum to our target customers, including the buyer of T-Mobile’s 800 MHz spectrum. In addition, many of the third parties who offer spectrum and communication technologies, products, services and solutions to our targeted customers have existing long-term relationships with these targeted customers and have significantly more resources and greater political and regulatory influence than we do, and we may not be able to successfully compete with these third parties;

•adverse market conditions, including as the result of tariffs and inflation, may adversely affect our business or the businesses of our target customers, which could have an adverse effect on our commercialization efforts;

•we may not generate funds through our commercialization operations as planned or correctly estimate our operating expenses, future cash proceeds or future revenues, which could lead to cash shortfalls, and may prevent us from returning capital to our stockholders and require us to secure additional financing;

•we have a unique business model, and our business activities, strategic approaches and plans may not be successful;

•we have had net losses most years since our inception and may not achieve or maintain profitability in the future;

•the value of our spectrum assets may fluctuate significantly based on supply and demand, as well as technical and regulatory changes;

•our plans to commercialize our 900 MHz spectrum assets depend on our ability to continue to qualify for and obtain broadband licenses from the FCC in accordance with the requirements of the Report and Order, including the enhanced standards required to qualify for the 5 x 5 MHz broadband licenses under the 2026 Report and Order;

•our voluntary exchange process established by the FCC in the Report and Order may not allow us to clear or relocate incumbents in certain counties in a timely manner and on commercially reasonable terms, or at all;

•the clearing process established by the FCC in the Report and Order, which exempts Complex Systems from mandatory retuning, may not allow us to retune or relocate incumbents in a timely manner and on commercially reasonable terms, or at all;

•our customers’ initiatives with the federal and state agencies and commissions that regulate electric utilities may not be successful, which may impact our commercialization efforts;

•we may not be able to maintain any narrowband and broadband licenses that we own and/or obtain from the FCC;

•government regulations or actions taken by governmental bodies could adversely affect our business prospects, liquidity and results of operations, including any changes by the FCC to the Report and Order or to the FCC rules and regulations governing the 900 MHz band;

•federal government shutdowns could affect our ability to obtain broadband licenses from the FCC, which could adversely impact our ability to comply with our contractual obligations and to commercialize our 900 MHz spectrum assets;

•our future success depends on our ability to retain our executive officers and key personnel and to attract, retain and motivate qualified personnel;

•concentration of ownership will limit our stockholders’ ability to influence corporate matters; and

•we may be unable to utilize the full value of the share repurchase program approved by our stockholders as expected, or at all.

Page 2