ADTN ADTRAN Holdings Inc

As filed with the Securities and Exchange Commission on November 18, 2024

Registration No. 333-   

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

ADTRAN Holdings, Inc.

(Exact name of registrant as specified in its charter)

901 Explorer Boulevard

Huntsville, Alabama 35806-2807

Tel No.: (256) 963-8000

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Ulrich Dopfer

Chief Financial Officer

ADTRAN Holdings, Inc.

901 Explorer Boulevard

Huntsville, Alabama 35806-2807

(256) 963-8000

(Name, address, including zip code, and telephone number, including area code, of agent for service)

With a copy to:

Timothy W. Gregg, Esq.

Maynard Nexsen PC

1901 Sixth Avenue North, Suite 1700

Birmingham, Alabama 35203

(205) 254-1000

Approximate date of commencement of proposed sale to the public: From time to time after this registration statement becomes effective.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box. ☐

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box. ☒

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ☐

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ☐

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 7(a)(2)(B) of the Securities Act. ☐

THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(A) OF THE SECURITIES ACT OF 1933, AS AMENDED, OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION 8(A), MAY DETERMINE.

The information in this prospectus is not complete and may be changed. These securities may not be sold until the registration statement filed with the Securities and Exchange Commission relating to these securities is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED NOVEMBER 18, 2024

PROSPECTUS

ADTRAN HOLDINGS, INC.

$200,000,000

Common Stock

Preferred Stock

Depositary Shares

Senior Debt Securities

Subordinated Debt Securities

Warrants

Purchase Contracts

Units

The securities listed above may be offered and sold by us from time to time in one or more offerings. The securities listed above may be offered separately or together in any combination, in one or more classes or series, in amounts, at prices and on terms that we will determine at the time of the offering. This prospectus also covers an indeterminate number of securities that may be issued upon exercise, conversion or exchange of any securities registered hereunder that provide for exercise, conversion or exchange or pursuant to the antidilution provisions of any such securities. The aggregate initial offering price of all securities sold by us pursuant to this prospectus will not exceed $200,000,000.

We will provide the specific terms of the securities to be offered in one or more supplements to this prospectus. The specific plan of distribution for any securities to be offered will also be provided in a prospectus supplement. Prospectus supplements may also add, update or change information in this prospectus. You should read this prospectus and the applicable prospectus supplement, together with additional information described under “Where You Can Find More Information,” carefully before you invest in our securities.

We may offer and sell these securities directly, through agents we select from time to time, or to or through underwriters or dealers that we select, or through a combination of these methods. If we use any agents, underwriters or dealers to sell the securities, we will name them and describe their compensation in a prospectus supplement. The price to the public of those securities and the net proceeds that we expect to receive from that sale will also be set forth in a prospectus supplement.

Our common stock is listed on The NASDAQ Global Select Market (“NASDAQ”) under the symbol “ADTN” and the Frankfurt Stock Exchange under the symbol “QH9.” On November 15, 2024, the last reported sale price of our common stock on NASDAQ was $7.75 per share. Each prospectus supplement will indicate if the securities offered thereby will be listed on any securities exchange.

This prospectus may not be used to sell securities unless accompanied by a prospectus supplement.

Investing in any of our securities involves certain risks. Please carefully read the section entitled “Risk Factors” on page 6 of this prospectus, as well as any risk factors included in, or incorporated by reference into, the applicable prospectus supplement, to read about factors you should consider before buying any securities issued by us.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is    , 2024.

TABLE OF CONTENTS

WE ARE RESPONSIBLE FOR THE INFORMATION CONTAINED AND INCORPORATED BY REFERENCE IN THIS PROSPECTUS AND ANY ACCOMPANYING PROSPECTUS SUPPLEMENT, AND IN ANY FREE WRITING PROSPECTUS THAT WE PREPARE. WE HAVE NOT AUTHORIZED ANYONE TO GIVE YOU ANY OTHER INFORMATION, AND WE TAKE NO RESPONSIBILITY FOR, AND CAN PROVIDE NO ASSURANCE AS TO THE RELIABILITY OF, ANY OTHER INFORMATION THAT OTHERS MAY GIVE YOU. THIS PROSPECTUS, ANY ACCOMPANYING PROSPECTUS SUPPLEMENT AND ANY SUCH FREE WRITING PROSPECTUS MAY BE USED ONLY FOR THE PURPOSES FOR WHICH THEY HAVE BEEN PREPARED. YOU SHOULD NOT ASSUME THAT THE INFORMATION CONTAINED OR INCORPORATED BY REFERENCE IN THIS PROSPECTUS IS ACCURATE AS OF ANY DATE OTHER THAN THE DATE OF THIS PROSPECTUS OR THE DATE OF THE RELEVANT INCORPORATED DOCUMENT, AS APPLICABLE. THE FINANCIAL CONDITION, RESULTS OF OPERATIONS OR BUSINESS PROSPECTS OF THE COMPANY MAY HAVE CHANGED SINCE THOSE DATES. WE ARE NOT MAKING AN OFFER OF THESE SECURITIES IN ANY JURISDICTION WHERE THE OFFER IS NOT PERMITTED.

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission (the “SEC”), using a “shelf” registration process. Under this shelf registration process, we may sell any of the securities, or any combination of the securities, described in this prospectus, in each case in one or more offerings up to a total dollar amount of gross proceeds of $200,000,000, subject to securities laws limitations.

This prospectus describes the general manner in which our securities may be offered by this prospectus. Each time we offer and sell securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. The prospectus supplement may include a discussion of any risk factors or other special considerations that apply to those securities. The prospectus supplement may also add, update or change information contained in this prospectus. If there is any inconsistency between the information in this prospectus (including the information incorporated by reference herein) and any prospectus supplement, you should rely on the information in that prospectus supplement.

Before you invest in any of the securities that we may sell, you should carefully read this prospectus, the accompanying prospectus supplement and the documents incorporated herein and therein. These documents contain important information you should consider when making your investment decision. This prospectus contains information about the securities we may offer generally. You should rely only on the information provided or incorporated by reference in this prospectus, any prospectus supplement, any free writing prospectus or any pricing supplement, and the documents incorporated by reference herein and therein, which are accurate as of their respective dates unless we indicate otherwise.

The registration statement containing this prospectus, including the exhibits to the registration statement, provides additional information about us and the securities offered under this prospectus. The registration statement can be read at the SEC’s website mentioned under the heading “Where You Can Find More Information.”

You should not consider any information in this prospectus, any prospectus supplement or any of the documents incorporated by reference herein or therein to be investment, legal or tax advice. You should consult your own counsel, accountants and other advisers for legal, tax, business, financial and related advice regarding the purchase of any securities.

We have not authorized anyone else to provide you with any information or to make any representation that is different from, or in addition to, those contained or incorporated by reference into this prospectus or any prospectus supplement, and, if given or made, such information or representations must not be relied upon as having been authorized by us.

The distribution of this prospectus and the applicable prospectus supplement and the offering of the securities in certain jurisdictions may be restricted by law. Persons into whose possession this prospectus and the applicable prospectus supplement come should inform themselves about and observe any such restrictions. This prospectus and the applicable prospectus supplement do not constitute, and may not be used in connection with, an offer or solicitation by anyone in any jurisdiction in which such offer or solicitation is not authorized or in which the person making such offer or solicitation is not qualified to do so or to any person to whom it is unlawful to make such offer or solicitation.

Unless otherwise indicated, all references in this prospectus to “$” or “dollars” are to U.S. dollars and financial information presented in this prospectus that is derived from financial statements incorporated by reference is prepared in accordance with accounting principles generally accepted in the United States (“U.S.”).

Unless the context otherwise indicates or requires, references in this prospectus to “ADTRAN,” the “Company,” “we,” “us” and “our” refer to ADTRAN Holdings, Inc. and its consolidated subsidiaries.

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WHERE YOU CAN FIND MORE INFORMATION

We are subject to the information reporting requirements of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and, in accordance with these requirements, we are required to file periodic reports and other information with the SEC. The reports and other information filed by us with the SEC are available to the public at the SEC’s website at http://www.sec.gov. In addition, you may obtain these materials on our website at http://www.adtran.com. Information on our website does not constitute part of this prospectus and should not be relied upon in connection with making any investment decision with respect to our securities.

We have filed with the SEC a registration statement on Form S-3 (the “registration statement,” which term shall encompass all amendments, exhibits, annexes and schedules thereto and all documents incorporated by reference therein) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), and the rules and regulations promulgated thereunder, with respect to the securities offered hereby. This prospectus, which constitutes a part of the registration statement, does not contain all the information contained in the registration statement, parts of which are omitted in accordance with the rules and regulations of the SEC. For further information with respect to us and the securities offered hereby, reference is made to the registration statement.

Forms of any indenture or other documents establishing the terms of the offered securities are filed as exhibits to the registration statement or will be filed through an amendment to the registration statement or under cover of a Current Report on Form 8-K and incorporated by reference in this prospectus or a prospectus supplement. Statements in this prospectus or any prospectus supplement about these documents are summaries and each statement is qualified in all respects by reference to the document to which it refers. You should refer to the actual documents for a more complete description of the relevant matters.

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INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” the information we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is an important part of this prospectus, and information that we file later with the SEC will automatically update and supersede the information included or incorporated by reference in this prospectus. In other words, in the case of a conflict or inconsistency between information contained in this prospectus and information incorporated by reference into this prospectus, you should rely on the information contained in the document that was filed later. We incorporate by reference in this prospectus the following documents and information (other than, in each case, documents or information deemed to have been furnished and not filed in accordance with SEC rules):

We also incorporate by reference in this prospectus each of the documents that we file with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act on or after the date of this prospectus and prior to the termination of the offerings under this prospectus and any prospectus supplement. We do not, however, incorporate by reference into this prospectus any documents or portions thereof that are not deemed “filed” with the SEC, including any information furnished pursuant to Item 2.02 or Item 7.01 of our Current Reports on Form 8-K on or after the date of this prospectus unless, and except to the extent, specified in such current reports.

We will provide to each person, including any beneficial owner, to whom a prospectus is delivered, a copy of any of these filings (other than an exhibit to these filings, unless the exhibit is specifically incorporated by reference into the filing requested) at no cost, upon a request to us by writing or telephoning us at the following address and telephone number:

ADTRAN Holdings, Inc.

Attn: Corporate Secretary

901 Explorer Boulevard

Huntsville, Alabama 35806-2807

(256) 963-8000

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, including the documents that we incorporate herein by reference, contains forward-looking statements within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act. These forward-looking statements are not historical facts, but only predictions and generally can be identified by use of statements that include phrases such as “will,” “may,” “should,” “continue,” “anticipate,” “believe,” “expect,” “plan,” “appear,” “project,” “estimate,” “intend,” “target,” “forecast,” or other words or phrases of similar import. Similarly, statements that describe our objectives, plans or goals are also forward-looking statements. These forward-looking statements are subject to risks and uncertainties, which could cause actual results to differ materially from those currently anticipated, including those discussed under the heading “Risk Factors” contained in this prospectus, any applicable prospectus supplement and any applicable free writing prospectus, and under similar headings in other documents that are incorporated by reference into this prospectus. Potential investors and other readers are urged to consider these risks and uncertainties carefully in evaluating the forward-looking statements and are cautioned not to place undue reliance on these forward-looking statements. The forward-looking statements included in this prospectus are made only as of the date of this prospectus, and we undertake no obligation to update publicly these forward-looking statements to reflect new information, future events or otherwise, except to the extent required by law. In light of these risks, uncertainties and assumptions, the forward-looking events might or might not occur. We cannot assure you that projected results, events, levels of activity, or performance will be achieved.

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THE COMPANY

Overview

We are a leading global provider of networking and communications platforms, software, systems and services focused on the broadband access and optical networking market. We are serving a diverse domestic and international customer base in multiple countries that includes large, medium and small service providers; alternative service providers, such as utilities, municipalities and fiber overbuilders; cable/ multiple system operators, small- to medium-sized businesses; distributed enterprises, including Fortune 500 companies with sophisticated business continuity applications; and federal, state and local government agencies. Our innovative solutions and services enable voice, data, video and internet-communications across a variety of network infrastructures and are currently in use by millions worldwide. We support our customers through our direct global sales organization and our distribution networks. Our success depends upon our ability to increase unit volume and market share through the introduction of new products and succeeding generations of products having optimal selling prices and increased functionality as compared to both the prior generation of a product and to the products of competitors in order to gain market share. To service our customers and grow revenue, we are continually conducting research, developing new products addressing customer needs and testing those products for the specific requirements of particular customers. We offer a broad portfolio of flexible software and hardware network solutions and services that enable network operators to meet today’s service demands while also enabling them to transition to the fully converged, scalable, highly automated, cloud-controlled voice, data, internet and video network of the future.

We solely own ADTRAN, Inc. and are the majority shareholder of Adtran Networks SE (“Adtran Networks”), formerly ADVA Optical Networking SE. ADTRAN, Inc. is a leading global provider of open, disaggregated networking and communications solutions. Adtran Networks is a global provider of network solutions for data, storage, voice and video services. We believe that the combined technology portfolio can best address current and future customer needs for high-speed connectivity from the network core to the end consumer, especially upon the convergence of solutions at the network edge.

General Information

Our predecessor, ADTRAN, Inc., began operations in January 1986. Incorporated in Delaware and headquartered in Huntsville, Alabama, we are located in Cummings Research Park – the second largest research park in the U.S. and fourth largest in the world. Our principal executive offices are located at 901 Explorer Boulevard, Huntsville, Alabama, 35806. Our telephone number at that location is (256) 963-8000. In addition to our corporate headquarters in Huntsville, Alabama, we have sales and research and development facilities in strategic global locations. Our website is www.adtran.com. Information on our website does not constitute part of this prospectus and should not be relied upon in connection with making any investment decision with respect to the offered securities.

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RISK FACTORS

An investment in our securities involves risk. Before making an investment decision, you should carefully consider the risks and uncertainties described under “Risk Factors” and “Cautionary Statement Regarding Forward-Looking Statements” in the applicable prospectus supplement and in our most recent Annual Report on Form 10-K, any updates to those risk factors in our most recent Quarterly Report on Form 10-Q and Current Reports on Form 8-K, including any amendments to such reports, incorporated in the registration statement of which this prospectus is a part, together with all other information contained and incorporated by reference in this prospectus and the applicable prospectus supplements. See “Where You Can Find More Information.” In addition to those risk factors, there may be additional risks and uncertainties of which management is not aware or focused on or that management deems immaterial. Our business, financial condition or results of operations could be materially adversely affected by any of these risks, and you could lose all or part of your investment. Our risk factors also include forward-looking statements, and our actual results may differ substantially from those discussed in such forward-looking statements. See “Cautionary Statement Regarding Forward-Looking Statements.”

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USE OF PROCEEDS

We intend to use the net proceeds from the sales of the securities in the manner and for the purposes set forth in the applicable prospectus supplement, which may include general corporate purposes.

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DESCRIPTION OF CAPITAL STOCK

The following description of our common stock is intended as a summary only and therefore is not a complete description of our common stock. This description is based upon, and is qualified by reference to, our amended and restated certificate of incorporation (“certificate of incorporation”), our amended and restated bylaws (“bylaws”) and applicable provisions of Delaware corporate law. You should read our certificate of incorporation and bylaws, which are filed as exhibits to the registration statement of which this prospectus forms a part, for the provisions that are important to you.

Authorized Capital Stock

Our authorized capital stock consists of 200 million shares of common stock, par value $0.01 per share, and 50 million shares of preferred stock, par value $0.01 per share. As of November 15, 2024, we had 79,305,919 shares of common stock outstanding, and no shares of preferred stock were outstanding.

Common Stock

Dividends

Holders of our common stock are entitled to receive proportionately any dividends as may be declared by our board of directors, in its discretion, out of funds legally available therefor, subject to any statutory or contractual restrictions on the payment of dividends and to any restrictions on the payment of dividends imposed by the terms of any outstanding preferred stock.

Voting Rights; Amendments to the Certificate of Incorporation

The holders of our common stock are entitled to one vote for each share upon all matters presented to the stockholders.

Under the Delaware General Corporation Law (the “DGCL”), the affirmative vote of a majority of the outstanding shares entitled to vote thereon and a majority of the outstanding stock of each class entitled to vote thereon is generally required to amend a corporation’s certificate of incorporation. Additionally, the holders of the outstanding shares of a class of a corporation’s capital stock are entitled to vote as a class upon a proposed amendment, whether or not entitled to vote thereon by the certificate of incorporation, if the amendment would increase or decrease the aggregate number of authorized shares of such class; increase or decrease the par value of the shares of such class; or alter or change the powers, preferences or special rights of the shares of such class so as to affect them adversely. Our certificate of incorporation does not alter this default amendment process.

Meetings of Stockholders

Our annual meeting of stockholders will be held at such place, if any, either within or without the State of Delaware, or by means of remote communication, and on such date and at such time as our board of directors may fix by resolution and as set forth in the notice of the meeting. Special meetings of stockholders will be held on such date and at such time and at such place, if any, either within or without the State of Delaware, as shall be designated in the notice of meeting or by means of remote communication. Unless otherwise prescribed by law, special meetings of stockholders may only be called at any time by the chairman of the board of directors, chief executive officer, or the president or by order of the board of directors. Except as otherwise required by law, our stockholders are not entitled to call special meetings of stockholders.

Except as otherwise prescribed by law, we will provide a notice of each meeting of stockholders, in the form of a writing or electronic transmission, no more than sixty (60) nor less than ten (10) days before the date of such meeting. The notice will include the place, if any; date and time of the meeting; the means of remote

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communications, if any, by which stockholders and proxy holders may be deemed to be present and vote at such meeting; the record date for determining the stockholders entitled to vote at the meeting, if such date is different from the record date for determining stockholders entitled to notice of the meeting; and, in the case of a special meeting, the purpose or purposes for which the meeting is called.

Conversion Rights

No conversion, redemption or sinking fund provisions apply to our common stock, and the holders of our common stock are not subject to calls or assessments by the Company.

Preemptive Rights

Holders of our common stock are not entitled to preemptive or subscription rights with respect to any sale, exchange, offering or issuance of shares of common stock or other securities of the Company.

Cumulative Voting

Holders of our common stock are not entitled to cumulative voting.

Form and Certification

Shares of our common stock are uncertificated. Shares of our common stock are created and maintained in book-entry form by our transfer agent and registrar, American Stock Transfer and Trust Company, LLC.

Stock Exchange Listing

Shares of our common stock are listed on the NASDAQ Global Select Market of The Nasdaq Stock Market LLC (“Nasdaq”) under the symbol “ADTN” and on the regulated market segment of the Frankfurt Stock Exchange under the symbol “QH9.”

Transfer Agent, Registrar, and Central Registration Agent

The transfer agent and registrar for the Company’s common stock is American Stock Transfer and Trust Company, LLC.

In order to facilitate the exercise of stockholders’ rights, in particular voting rights and participation in meetings of stockholders of the Company via Clearstream, we entered into an agreement with ADEUS Aktregister-Services-GmbH, Königinstrasse 28, 80802 Munich, Germany, which acts as the central registration office. The tasks of the central registration office include the publication of all relevant information required by stockholders to exercise their rights in the German Federal Gazette (Bundesanzeiger), as well as the assumption of administrative tasks within the logistics of participation and voting rights at general meetings of stockholders. We maintain either the central registration office or a comparable service provider.

Preferred Stock

Under our certificate of incorporation, our board of directors is authorized, without further stockholder action, to provide, out of the unissued shares of preferred stock, for one or more series of preferred stock and, with respect to each such series, to fix, without further stockholder approval, the designation of such series, the powers (including voting powers), preferences and relative, participating, optional and other special rights, and the qualifications, limitations or restrictions thereof, of such series of preferred stock and the number of shares of

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such series, and as may be permitted by the DGCL. The powers, preferences and relative, participating, optional and other special rights of, and the qualifications, limitations or restrictions thereof, each series of Preferred Stock, if any, may differ from those of any and all other series at any time outstanding.

We will fix the designations, voting powers, preferences and rights of the preferred stock of each series we issue under this prospectus, as well as the qualifications, limitations or restrictions thereof, in the certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that contains the terms of the series of preferred stock we are offering. We will describe in the applicable prospectus supplement the terms of the series of preferred stock being offered, including, to the extent applicable:

General Provisions Governing a Change in Authorized Share Capital; Issuance of Common Stock

The DGCL provides that the authorized number of shares of a Delaware corporation must be set forth in the certificate of incorporation. Under the DGCL, our stockholders may authorize an increase in the number of authorized shares by approving an amendment to the certificate of incorporation.

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Delaware law does not require stockholder approval for any issuance of authorized shares. However, the listing requirements of Nasdaq, which apply as long as our common stock is listed on Nasdaq, require stockholder approval of certain issuances equal to or exceeding 20% of the combined voting power of our common stock. These additional shares may be used for a variety of corporate purposes, including future public offerings to raise additional capital, acquisitions and employee benefit plans.

The existence of unissued and unreserved common stock may enable our board of directors to issue shares to persons friendly to current management, which could render more difficult or discourage an attempt to obtain control of the Company by means of a merger, tender offer, proxy contest or otherwise, and could thereby protect the continuity of our management and possibly deprive stockholders of opportunities to sell their shares of common stock at prices higher than prevailing market prices.

General Provisions Governing a Liquidation of the Company; Liquidation Distributions

Upon the liquidation, dissolution or winding up of the Company, any business combination or a sale or disposition of all or substantially all of the Company’s assets, the assets legally available for distribution to the Company’s stockholders will be distributable ratably among the holders of our common stock, subject to prior satisfaction of all outstanding debts and other liabilities and the payment of liquidation preferences, if any, on any outstanding preferred stock.

Anti-Takeover Effects of Delaware Law and Our Certificate of Incorporation and Bylaws

Certain provisions of the DGCL, our certificate of incorporation, and our bylaws could make the acquisition of the Company more difficult and could delay, defer or prevent a tender offer or other takeover attempt that a stockholder might consider to be in its best interest, including takeover attempts that might result in the payment of a premium to stockholders over the market price for their shares. These provisions also may promote the continuity of our management by making it more difficult for a person to remove or change the incumbent members of our board of directors.

Authorized but Unissued Preferred Stock

The authorized but unissued shares of our preferred stock are available for future issuance without stockholder approval except as required by law or by any stock exchange on which our common stock may be listed. Our board of directors is authorized to provide for the issuance of shares of our preferred stock in one or more classes or series, and to fix the powers for each class or series (including voting powers), preferences and relative, participating, optional and other special rights and any qualifications, limitations or restrictions thereof as may be permitted by the DGCL. These additional shares may be utilized for a variety of corporate purposes, including future public offerings to raise additional capital, acquisitions and employee benefit plans. The existence of authorized but unissued shares of preferred stock may enable our board of directors to render more difficult or to discourage an attempt to obtain control of us by means of a merger, tender offer, proxy contest or otherwise.

No Cumulative Voting

Our certificate of incorporation does not permit stockholders to cumulate votes in the election of directors.

Special Meetings of Stockholders

Our bylaws provide that, except as otherwise required by law, special meetings of stockholders can only be called by the chairman of the board of directors, the chief executive officer, the president or the board of directors.

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Stockholder Action by Written Consent

Our bylaws provide that any action required to be taken at any annual or special meeting of the stockholders may be taken without a meeting, without prior notice and without a vote if a consent or consents in writing, setting forth the action so taken and bearing the dates of the stockholders who signed the consent, is signed by the holders of outstanding stock having not less than the minimum number of votes that would be necessary to authorize or take such action at a meeting at which all shares of our stock entitled to vote thereon were present and voted, unless our certificate of incorporation provides otherwise. Such written consent must be delivered by hand or by certified or registered mail, return receipt requested and no written consent shall be effective to take the corporate action referred to therein unless, within 60 days of the earliest dated written consent received in accordance with the bylaws, a written consent or consents signed by a sufficient number of holders to take such action is delivered to the Company. Prompt notice of the taking of such action without a meeting and by less than unanimous written consent shall be given to those stockholders who have not consented in writing.

Advance Notice Requirements for Stockholder Proposals and Nomination of Directors

Our bylaws require stockholders seeking to bring business before an annual meeting of stockholders, or to nominate individuals for election as directors at an annual or special meeting of stockholders, to provide timely notice in writing. To be timely, a stockholder’s notice must be properly furnished to the Company, in the case of an annual meeting, no later than the close of business on the ninetieth (90th) day, nor earlier than the close of business on the one hundred twentieth (120th) day, prior to the first anniversary of the preceding year’s annual meeting; provided, however, that subject to the immediately following sentence, in the event that the annual meeting is convened more than thirty (30) days before or more than seventy (70) days after such anniversary date, or if no annual meeting was held in the preceding year, notice by the stockholder must be so received no earlier than the close of business on the one hundred twentieth (120th) day prior to such annual meeting and no later than the close of business on the later of the ninetieth (90th) day prior to such annual meeting or the tenth (10th) day following the day on which public announcement of the date of such meeting is first made by the Company. Our bylaws also specify requirements as to the form and content of a stockholder’s notice. These provisions may preclude our stockholders from bringing matters before the annual meeting of stockholders or from making nominations for directors at meetings of stockholders. These provisions may also discourage or deter a potential acquirer from conducting a solicitation of proxies to elect the potential acquirer’s own slate of directors or otherwise attempting to obtain control of the Company.

Removal of Directors; Vacancies

Subject to our Director Resignation Policy, any director or the entire board of directors may be removed, with or without cause, by the holders of a majority of the shares of our capital stock then entitled to vote in an election of directors, except as otherwise provided by applicable law. In addition, any newly created directorship on our board of directors that results from an increase in the number of directors and any vacancy occurring in our board of directors may only be filled by a majority of the directors then in office, although less than a quorum, or by a sole remaining director (and not by the stockholders).

Director Resignations

Director candidates must agree to tender, promptly following the annual meeting at which they are to be elected or re-elected as director, an irrevocable resignation in writing, which shall become effective only if (i) the director fails to receive a sufficient number of votes for an election in an uncontested election of directors and (ii) the board of directors accepts their resignation in accordance with the Director Resignation Policy. Once an incumbent director fails to receive a sufficient number of votes for election in an uncontested election, our Nominating and Corporate Governance Committee will consider on an expedited basis such director’s tendered resignation and make a recommendation to the board of directors concerning the acceptance or rejection of such resignation (or any potential alternatives, including the rejection of the resignation coupled with a commitment to seek to address and cure the underlying reasons believed by the Nominating and Corporate Governance

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Committee in good faith to have substantially resulted in such director failing to receive the requisite votes). The board of directors will then expeditiously take formal action following the certification of the election results from the stockholders’ meeting at which the election occurred.

Delaware Business Combination Statute

Section 203 of the DGCL provides that, subject to certain stated exceptions, a corporation may not engage in a business combination with any “interested stockholder” (as defined below) for a period of three years following the time that such stockholder became an interested stockholder, unless:

An “interested stockholder” is, subject to certain exceptions, any person (other than the corporation and any direct or indirect majority-owned subsidiary) who owns 15% or more of the outstanding voting stock of the corporation or is an affiliate or associate of the corporation and was the owner of 15% or more of the outstanding voting stock of the corporation at any time within the three-year period immediately prior to the date of determination, and the affiliates and associates of such person.

A Delaware corporation may “opt out” of these provisions with an express provision in its original certificate of incorporation or an express provision in its certificate of incorporation or bylaws resulting from a stockholders’ amendment approved by at least a majority of the outstanding voting shares. We have not opted out of Section 203 of the DGCL and are subject to the provisions therein.

Exclusive Forum

Our certificate of incorporation provides that, unless we consent in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware will, to the fullest extent permitted by law, be the sole and exclusive forum for: (i) any derivative action or proceeding brought on our behalf; (ii) any action asserting a breach of fiduciary duty owed by any of our directors, officers, other employees or stockholders to us or our stockholders, creditors or other constituents, or a claim of aiding and abetting any such breach of fiduciary duty; (iii) any action asserting a claim against the us or our directors or officers arising pursuant to any provision of the DGCL or our certificate of incorporation or bylaws (as either may be amended and/or restated from time to time) or as to which the DGCL confers jurisdiction on the Court of Chancery of the State of Delaware; (iv) any action to interpret, apply, enforce or determine the validity of our certificate of incorporation or bylaws (as either may be amended and/or restated from time to time); (v) any action asserting a claim against us or our directors or officers that is governed by the internal affairs doctrine; or (vi) any action asserting an “internal corporate claim” as that term is defined in Section 115 of the DGCL; provided, however, that, in the event that the Court of Chancery of the State of Delaware lacks subject matter jurisdiction over any such action or proceeding, any other state court of the State of Delaware, or if no state court of the State of Delaware has subject matter jurisdiction, the federal district court for the District of Delaware will be the forum.

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Additionally, to prevent having to litigate claims in multiple jurisdictions and the threat of inconsistent or contrary rulings by different courts, among other considerations, our certificate of incorporation provides that, unless we consent in writing to the selection of an alternative forum, the federal district courts of the U.S. will be the sole and exclusive forum for the resolution of any complaint asserting a cause of action arising under the federal securities laws.

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DESCRIPTION OF DEPOSITARY SHARES

We may offer fractional interests in shares of preferred stock rather than full shares of preferred stock. In that event, depositary receipts will be issued to evidence depositary shares, each of which will represent a fraction of a share of a particular series of preferred stock, as described in the prospectus supplement relating to the particular issue of depositary shares.

The shares of preferred stock represented by depositary shares will be deposited under a deposit agreement between us and a depositary that is a bank or trust company, as depositary, that we will select as set forth in the prospectus supplement relating to the particular issue of depositary shares. Unless otherwise specified in the prospectus supplement relating to a particular issue of depositary shares, each owner of a depositary share will be entitled, in proportion to the applicable fraction of a share of preferred stock represented by such depositary share, to all the rights and preferences of the shares of preferred stock represented by such depositary share, including dividend and liquidation rights and any right to convert the shares of preferred stock into common stock.

We will describe the terms of any depositary shares we offer and the related deposit agreement, as well as the terms of the shares of preferred stock represented thereby, in the prospectus supplement relating to the particular issue of depositary shares.

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DESCRIPTION OF DEBT SECURITIES

The following description summarizes the general terms and provisions of the debt securities that we may offer and sell from time to time. We will describe the specific terms of the debt securities offered through a prospectus supplement, as well as any general terms and provisions described in this section that will not apply to those debt securities. As used in this “Description of Debt Securities” the term “debt securities,” means the senior and subordinated debt securities that we issue and the trustee authenticates and delivers under the applicable indenture. When we refer to “the Company,” “we,” “our,” and “us” in this section, we mean ADTRAN Holdings, Inc. excluding, unless the context otherwise requires or as otherwise expressly stated, its subsidiaries.

We may issue senior debt securities from time to time, in one or more series under a senior indenture to be entered into between us and a senior trustee to be named in a prospectus supplement, which we refer to as the senior trustee. We may issue subordinated debt securities from time to time, in one or more series under a subordinated indenture to be entered into between us and a subordinated trustee to be named in a prospectus supplement, which we refer to as the subordinated trustee. The forms of senior indenture and subordinated indenture are filed as exhibits to the registration statement of which this prospectus forms a part. The senior indenture and the subordinated indenture are referred to individually as an indenture and together as the indentures and the senior trustee and the subordinated trustee are referred to individually as a trustee and together as the trustees. This section summarizes some of the provisions of the indentures and is qualified in its entirety by the specific text of the indentures, including definitions of terms used in the indentures. Wherever we refer to particular sections of, or defined terms in, the indentures, those sections or defined terms are incorporated by reference in this prospectus or the applicable prospectus supplement. You should review the indentures that are filed as exhibits to the registration statement of which this prospectus forms a part for additional information.

Neither indenture will limit the amount of debt securities that we may issue. The applicable indenture will provide that debt securities may be issued up to an aggregate principal amount authorized from time to time by us and may be payable in any currency or currency unit designated by us or in amounts determined by reference to an index.

General

The senior debt securities will constitute our unsecured and unsubordinated general obligations and will rank equally in right of payment with our other unsecured and unsubordinated obligations. The subordinated debt securities will constitute our unsecured and subordinated general obligations and will be junior in right of payment to our senior indebtedness (including senior debt securities), as described under the heading “—Certain Terms of the Subordinated Debt Securities—Subordination.” The debt securities will be structurally subordinated to all existing and future indebtedness and other liabilities of our subsidiaries unless such subsidiaries expressly guarantee such debt securities.

The debt securities will be our unsecured obligations. Any secured debt or other secured obligations will be effectively senior to the debt securities to the extent of the value of the assets securing such debt or other obligations.

The applicable prospectus supplement and/or free writing prospectus will include any additional or different terms of the debt securities of any series being offered, including the following terms:

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When we refer to “principal” in this section with reference to the debt securities, we are also referring to “premium, if any.”

We may from time to time, without notice to or the consent of the holders of any series of debt securities, create and issue further debt securities of any such series ranking equally with the debt securities of such series in all respects (or in all respects other than (1) the payment of interest accruing prior to the issue date of such further debt securities or (2) the first payment of interest following the issue date of such further debt securities). Such further debt securities may be consolidated and form a single series with the debt securities of such series and have the same terms as to status, redemption or otherwise as the debt securities of such series.

You may present debt securities for exchange and you may present debt securities for transfer in the manner, at the places and subject to the restrictions set forth in the debt securities and the applicable prospectus supplement. We will provide you those services without charge, although you may have to pay any tax or other governmental charge payable in connection with any exchange or transfer, as set forth in the indenture.

Debt securities may bear interest at a fixed rate or a floating rate. Debt securities bearing no interest or interest at a rate that at the time of issuance is below the prevailing market rate (original issue discount securities) may be sold at a discount below their stated principal amount. U.S. federal income tax considerations applicable to any such discounted debt securities or to certain debt securities issued at par which are treated as having been issued at a discount for U.S. federal income tax purposes will be described in the applicable prospectus supplement.

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We may issue debt securities with the principal amount payable on any principal payment date, or the amount of interest payable on any interest payment date, to be determined by reference to one or more currency exchange rates, securities or baskets of securities, commodity prices or indices. You may receive a payment of principal on any principal payment date, or a payment of interest on any interest payment date, that is greater than or less than the amount of principal or interest otherwise payable on such dates, depending on the value on such dates of the applicable currency, security or basket of securities, commodity or index. Information as to the methods for determining the amount of principal or interest payable on any date, the currencies, securities or baskets of securities, commodities or indices to which the amount payable on such date is linked and certain related tax considerations will be set forth in the applicable prospectus supplement.

Certain Terms of the Senior Debt Securities

Covenants. Unless we indicate otherwise in a prospectus supplement with respect to a particular series of senior debt securities, the senior debt securities will not contain any financial or restrictive covenants, including covenants restricting either us or any of our subsidiaries from incurring, issuing, assuming or guaranteeing any indebtedness secured by a lien on any of our or our subsidiaries’ property or capital stock, or restricting either us or any of our subsidiaries from entering into sale and leaseback transactions.

Consolidation, Merger and Sale of Assets. Unless we indicate otherwise in a prospectus supplement with respect to a particular series of senior debt securities, we may not consolidate with or merge into any other person, in a transaction in which we are not the surviving corporation, or convey, transfer or lease our properties and assets substantially as an entirety to any person, in either case, unless:

The restrictions described in the bullets above do not apply (1) to our consolidation with or merging into one of our affiliates, if our board of directors determines in good faith that the purpose of the consolidation or merger is principally to change our state of incorporation or our form of organization to another form or (2) if we merge with or into a single direct or indirect wholly-owned subsidiary of ours.

The surviving business entity will succeed to, and be substituted for, us under the senior indenture and the senior debt securities and, except in the case of a lease, we shall be released from all obligations under the senior indenture and the senior debt securities.

No Protection in the Event of a Change in Control. Unless we indicate otherwise in a prospectus supplement with respect to a particular series of senior debt securities, the senior debt securities will not contain any provisions that may afford holders of the senior debt securities protection in the event we have a change in control or in the event of a highly leveraged transaction (whether or not such transaction results in a change in control).

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Events of Default. Unless we indicate otherwise in a prospectus supplement with respect to a particular series of senior debt securities, the following are events of default under the senior indenture with respect to senior debt securities of each series:

Unless we indicate otherwise in a prospectus supplement with respect to a particular series of senior debt securities, the default by us under any other debt, including any other series of our debt securities, is not a default under the senior indenture.

If an event of default other than an event of default specified in the fourth bullet point above occurs with respect to a series of senior debt securities and is continuing under the senior indenture, then, and in each such case, either the trustee or the holders of not less than 25% in aggregate principal amount of such series then outstanding under the senior indenture (each such series voting as a separate class) by written notice to us and to the trustee, if such notice is given by the holders, may, and the trustee at the request of such holders shall, declare the principal amount of and accrued interest on such series of senior debt securities to be immediately due and payable, and upon this declaration, the same shall become immediately due and payable.

If an event of default specified in the fourth bullet point above occurs and is continuing, the entire principal amount of and accrued interest on each series of senior debt securities then outstanding shall automatically become immediately due and payable.

Unless otherwise specified in the prospectus supplement relating to a series of senior debt securities originally issued at a discount, the amount due upon acceleration shall include only the original issue price of the senior debt securities, the amount of original issue discount accrued to the date of acceleration and accrued interest, if any.

Upon certain conditions, declarations of acceleration may be rescinded and annulled and past defaults may be waived by the holders of a majority in aggregate principal amount of all the senior debt securities of such series affected by the default, each series voting as a separate class. Furthermore, subject to various provisions in the senior indenture, the holders of a majority in aggregate principal amount of a series of senior debt securities, by notice to the trustee, may waive a continuing default or event of default with respect to such senior debt securities and its consequences, except a default in the payment of principal of or interest on such senior debt securities (other than any such default in payment resulting solely from an acceleration of the senior debt securities) or in respect of a covenant or provision of the senior indenture which cannot be modified or amended without the consent of the holders of each such senior debt security. Upon any such waiver, such default shall cease to exist, and any event of default with respect to such senior debt securities shall be deemed to have been cured, for every purpose of the senior indenture; but no such waiver shall extend to any subsequent or other default or event of default or impair any right consequent thereto.

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The holders of a majority in aggregate principal amount of a series of senior debt securities may direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred on the trustee with respect to such senior debt securities. However, the trustee may refuse to follow any direction that conflicts with law or the senior indenture, that may involve the trustee in personal liability or that the trustee determines in good faith may be unduly prejudicial to the rights of holders of such series of senior debt securities not joining in the giving of such direction and may take any other action it deems proper that is not inconsistent with any such direction received from holders of such series of senior debt securities. A holder may not pursue any remedy with respect to the senior indenture or any series of senior debt securities unless:

These limitations, however, do not apply to the right of any holder of a senior debt security of any affected series to receive payment of the principal of and interest on such senior debt security in accordance with the terms of such debt security, or to bring suit for the enforcement of any such payment in accordance with the terms of such debt security, on or after the due date for the senior debt securities, which right shall not be impaired or affected without the consent of the holder.

The senior indenture requires certain of our officers to certify, on or before a fixed date in each year in which any senior debt security is outstanding, as to their knowledge of our compliance with all covenants, agreements and conditions under the senior indenture.

Satisfaction and Discharge. We can satisfy and discharge our obligations to holders of any series of debt securities if:

and if, in any such case, we also pay or cause to be paid all other sums payable under the senior indenture, as and when the same shall be due and payable and we deliver to the senior trustee an officer’s certificate and an opinion of counsel, each stating that these conditions have been satisfied.

Under current U.S. federal income tax law, the deposit and our legal release from the debt securities would be treated as though we took back your debt securities and gave you your share of the cash and debt securities or

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bonds deposited in trust. In that event, you could recognize gain or loss on the debt securities you give back to us. Purchasers of the debt securities should consult their own advisers with respect to the tax consequences to them of such deposit and discharge, including the applicability and effect of tax laws other than the U.S. federal income tax law.

Defeasance. Unless the applicable prospectus supplement provides otherwise, the following discussion of legal defeasance and covenant defeasance will apply to any series of debt securities issued under the indentures.

Legal Defeasance. We can legally release ourselves from any payment or other obligations on the debt securities of any series (called “legal defeasance”) if certain conditions are met, including the following:

If we accomplish legal defeasance, as described above, you would have to rely solely on the trust deposit for repayment of the debt securities. You could not look to us for repayment in the event of any shortfall.

Covenant Defeasance. Without any change in current U.S. federal tax law, we can make the same type of deposit described above and be released from some of the covenants in the debt securities (called “covenant defeasance”). In that event, you would lose the protection of those covenants but would gain the protection of having money and securities set aside in trust to repay the debt securities. In order to achieve covenant defeasance, we must do the following (among other things):

If we accomplish covenant defeasance, you could still look to us for repayment of the debt securities if there were a shortfall in the trust deposit. In fact, if one of the events of default occurred (such as our bankruptcy) and the debt securities become immediately due and payable, there may be such a shortfall. Depending on the events causing the default, you may not be able to obtain payment of the shortfall.

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Modification and Waiver. We and the trustee may amend or supplement the senior indenture or the senior debt securities of any series without the consent of any holder:

Other amendments and modifications of the senior indenture or the senior debt securities issued may be made, and our compliance with any provision of the senior indenture with respect to any series of senior debt securities may be waived, with the consent of the holders of a majority of the aggregate principal amount of the outstanding senior debt securities of each series affected by the amendment or modification (voting as separate series); provided, however, that each affected holder must consent to any modification, amendment or waiver that:

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It shall not be necessary for the holders to approve the particular form of any proposed amendment, supplement or waiver, but it shall be sufficient if the holders’ consent approves the substance thereof. After an amendment, supplement or waiver of the senior indenture in accordance with the provisions described in this section becomes effective, the trustee must give to the holders affected thereby certain notice briefly describing the amendment, supplement or waiver. Any failure by the trustee to give such notice, or any defect therein, shall not, however, in any way impair or affect the validity of any such amendment, supplemental indenture or waiver.

Notice of Redemption. Notice of any redemption of senior debt securities will be mailed at least 10 days but not more than 60 days before the redemption date to each holder of senior debt securities of a series to be redeemed. Any notice may, at our discretion, be subject to the satisfaction or waiver of one or more conditions precedent. In that case, such notice shall state the nature of such condition precedent. If we elect to redeem a portion but not all of such senior debt securities, the trustee will select the senior debt securities to be redeemed in a method determined manner that complies with applicable legal and stock exchange requirements, if any. Interest on such debt securities or portions of senior debt securities will cease to accrue on and after the date fixed for redemption, unless we default in the payment of such redemption price and accrued interest with respect to any such senior debt security or portion thereof.

If any date of redemption of any senior debt security is not a business day, then payment of principal and interest may be made on the next succeeding business day with the same force and effect as if made on the nominal date of redemption and no interest will accrue for the period after such nominal date.

Conversion or Exchange Rights. We will describe the terms upon which senior debt securities may be convertible into or exchangeable for our common stock or other securities in a prospectus supplement. These terms will include the type of securities that the senior debt securities are convertible into or exchangeable for, the conversion or exchange price or manner of calculation thereof, the conversion or exchange period, provisions as to whether conversion or exchange will be at our option or the option of the holders, the events requiring an adjustment of the conversion or exchange price and provisions affecting conversion or exchange in the event of the redemption of the senior debt securities and any restrictions on conversion or exchange. They may also include provisions adjusting the number of shares of our common stock or other securities issuable upon conversion or exchange.

No Personal Liability of Incorporators, Stockholders, Officers, or Directors. The senior indenture provides that no recourse shall be had under any obligation, covenant or agreement of ours in the senior indenture or any

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supplemental indenture, or in any of the senior debt securities or because of the creation of any indebtedness represented thereby, against any of our incorporators, stockholders, officers or directors, past, present or future, or of any predecessor or successor entity thereof under any law, statute or constitutional provision or by the enforcement of any assessment or by any legal or equitable proceeding or otherwise. Each holder, by accepting the senior debt securities, waives and releases all such liability.

Concerning the Trustee. The senior indenture provides that, except during the continuance of an event of default, the trustee will not be liable except for the performance of such duties as are specifically set forth in the senior indenture. If an event of default has occurred and is continuing, the trustee will exercise such rights and powers vested in it under the senior indenture and will use the same degree of care and skill in its exercise as a prudent person would exercise under the circumstances in the conduct of such person’s own affairs.

The senior indenture and the provisions of the Trust Indenture Act incorporated by reference therein contain limitations on the rights of the trustee thereunder, should it become a creditor of ours or any of our subsidiaries, to obtain payment of claims in certain cases or to realize on certain property received by it in respect of any such claims, as security or otherwise. The trustee is permitted to engage in other transactions, provided that if it acquires any conflicting interest (as defined in the Trust Indenture Act), it must eliminate such conflict or resign.

We may have normal banking relationships with the senior trustee in the ordinary course of business.

Unclaimed Funds. All funds deposited with the trustee or any paying agent for the payment of principal, premium, interest or additional amounts in respect of the senior debt securities that remain unclaimed for two years after the date upon which such amounts became due and payable will be repaid to us. Thereafter, any right of any holder of senior debt securities to such funds shall be enforceable only against us, and the trustee and paying agents will have no liability therefor.

Governing Law. The senior indenture and the senior debt securities will be governed by, and construed in accordance with, the internal laws of the State of New York.

Certain Terms of the Subordinated Debt Securities

Other than the terms of the subordinated indenture and subordinated debt securities relating to subordination or otherwise as described in the prospectus supplement relating to a particular series of subordinated debt securities, the terms of the subordinated indenture and subordinated debt securities are identical in all material respects to the terms of the senior indenture and senior debt securities.

Additional or different subordination terms may be specified in the prospectus supplement applicable to a particular series.

Subordination. The indebtedness evidenced by the subordinated debt securities is subordinate to the prior payment in full of all of our senior indebtedness, as defined in the subordinated indenture. During the continuance beyond any applicable grace period of any default in the payment of principal, premium, interest or any other payment due on any of our senior indebtedness, we may not make any payment of principal of or interest on the subordinated debt securities (except for certain sinking fund payments). In addition, upon any payment or distribution of our assets upon any dissolution, winding-up, liquidation or reorganization, the payment of the principal of and interest on the subordinated debt securities will be subordinated to the extent provided in the subordinated indenture in right of payment to the prior payment in full of all our senior indebtedness. Because of this subordination, if we dissolve or otherwise liquidate, holders of our subordinated debt securities may receive less, ratably, than holders of our senior indebtedness. The subordination provisions do not prevent the occurrence of an event of default under the subordinated indenture.

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The term “senior indebtedness” of a person means with respect to such person the principal of, premium, if any, interest on, and any other payment due pursuant to any of the following, whether outstanding on the date of the subordinated indenture or incurred by that person in the future:

unless, in the case of any particular indebtedness, renewal, extension or refunding, the instrument creating or evidencing it or the assumption or guarantee relating to it expressly provides that such indebtedness, renewal, extension or refunding is not superior in right of payment to the subordinated debt securities. Our senior debt securities, if any, constitute senior indebtedness for purposes of the subordinated indenture.

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DESCRIPTION OF WARRANTS

We may issue warrants, including warrants to purchase common stock, preferred stock, depositary shares, or other securities of the Company described in this prospectus or a prospectus supplement, or any combination of the foregoing. Warrants may be issued independently or together with any securities and may be attached to or separate from the securities. The warrants will be issued under warrant agreements to be entered into between us and a warrant agent as detailed in the prospectus supplement relating to the warrants being offered.

The applicable prospectus supplement will describe the following terms, where applicable, of the warrants in respect of which this prospectus is being delivered:

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DESCRIPTION OF PURCHASE CONTRACTS

We may issue purchase contracts, including contracts obligating holders to purchase from us, and obligating us to sell to holders, a specified number of shares of common stock, preferred stock, depositary shares, or debt securities offered hereby at a future date or dates, which we refer to in this prospectus as “purchase contracts.” The price per share or other security and the number of securities may be fixed at the time the purchase contracts are issued or may be determined by reference to a specific formula set forth in the purchase contracts. The purchase contracts may require holders to secure their obligations under the purchase contracts in a specified manner. The purchase contracts may be convertible into or exercisable for common stock, preferred stock, depositary shares, or debt securities of ours or debt or equity securities of one or more other entities.

An accompanying prospectus supplement will describe the terms of the purchase contracts and, if applicable, collateral or depositary arrangements relating to the purchase contracts. Material U.S. federal income tax considerations applicable to the purchase contracts will also be discussed in the applicable prospectus supplement.

Unless otherwise specified in an accompanying prospectus supplement, each purchase contract and any related agreement will be governed by, and construed in accordance with, the laws of the State of Delaware.

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DESCRIPTION OF UNITS

We may issue units comprised of one or more of the other classes of securities described in this prospectus in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately at any time or at any time before a specified date or occurrence. The units may be issued under unit agreements to be entered into between us and a unit agent, as detailed in the applicable prospectus supplement relating to the units being offered.

To the extent appropriate, the applicable prospectus supplement will describe the specific terms of any units offered thereby, including the following:

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PLAN OF DISTRIBUTION

We may sell the securities covered by this prospectus from time to time in one or more offerings. Registration of the securities covered by this prospectus does not mean, however, that those securities will necessarily be offered or sold.

We may sell our securities, separately or together, in any one or more of the following ways:

The securities may be distributed from time to time in one or more transactions:

Each prospectus supplement will indicate if the securities offered thereby will be listed on any securities exchange.

Offers to purchase the securities being offered by this prospectus may be solicited directly. Agents may also be designated to solicit offers to purchase the securities from time to time. Any agent involved in the offer or sale of our securities will be identified in a prospectus supplement.

If a dealer is utilized in the sale of the securities being offered by this prospectus, the securities will be sold to the dealer, as principal. The dealer may then resell the securities to the public at varying prices to be determined by the dealer at the time of resale.

If an underwriter is utilized in the sale of the securities being offered by this prospectus, an underwriting agreement will be executed with the underwriter at the time of sale and the name of any underwriter will be provided in the prospectus supplement that the underwriter will use to make resales of the securities to the public. In connection with the sale of the securities, we or the purchasers of securities for whom the underwriter may act as agent, may compensate the underwriter in the form of underwriting discounts or commissions. The underwriter may sell the securities to or through dealers, and those dealers may receive compensation in the form of discounts, concessions or commissions from the underwriters and/or commissions from the purchasers for which they may act as agent. Unless otherwise indicated in a prospectus supplement, an agent will be acting on a best efforts basis and a dealer will purchase securities as a principal, and may then resell the securities at varying prices to be determined by the dealer.

Any compensation paid to underwriters, dealers or agents in connection with the offering of the securities, and any discounts, concessions or commissions allowed by underwriters to participating dealers will be provided

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in the applicable prospectus supplement. Underwriters, dealers and agents participating in the distribution of the securities may be deemed to be underwriters within the meaning of the Securities Act, and any discounts and commissions received by them and any profit realized by them on resale of the securities may be deemed to be underwriting discounts and commissions. We may enter into agreements to indemnify underwriters, dealers and agents against civil liabilities, including liabilities under the Securities Act, or to contribute to payments they may be required to make in respect thereof and to reimburse those persons for certain expenses.

The securities may or may not be listed on a national securities exchange. To facilitate the offering of securities, certain persons participating in the offering may engage in transactions that stabilize, maintain or otherwise affect the price of the securities. This may include over-allotments or short sales of the securities, which involve the sale by persons participating in the offering of more securities than were sold to them. In these circumstances, these persons would cover such over-allotments or short positions by making purchases in the open market or by exercising their over-allotment option, if any. In addition, these persons may stabilize or maintain the price of the securities by bidding for or purchasing securities in the open market or by imposing penalty bids, whereby selling concessions allowed to dealers participating in the offering may be reclaimed if securities sold by them are repurchased in connection with stabilization transactions. The effect of these transactions may be to stabilize or maintain the market price of the securities at a level above that which might otherwise prevail in the open market. These transactions may be discontinued at any time.

If indicated in the applicable prospectus supplement, underwriters or other persons acting as agents may be authorized to solicit offers by institutions or other suitable purchasers to purchase the securities at the public offering price set forth in the prospectus supplement, pursuant to delayed delivery contracts providing for payment and delivery on the date or dates stated in the prospectus supplement. These purchasers may include, among others, commercial and savings banks, insurance companies, pension funds, investment companies and educational and charitable institutions. Delayed delivery contracts will be subject to the condition that the purchase of the securities covered by the delayed delivery contracts will not at the time of delivery be prohibited under the laws of any jurisdiction in the U.S. to which the purchaser is subject. The underwriters and agents will not have any responsibility with respect to the validity or performance of these contracts.

We may engage in at-the-market offerings into an existing trading market in accordance with Rule 415(a)(4) under the Securities Act. In addition, we may enter into derivative transactions with third parties, or sell securities not covered by this prospectus to third parties in privately negotiated transactions. If the applicable prospectus supplement so indicates, in connection with those derivatives, the third parties may sell securities covered by this prospectus and the applicable prospectus supplement, including in short sale transactions. If so, the third party may use securities pledged by us or borrowed from us or others to settle those sales or to close out any related open borrowings of common stock, and may use securities received from us in settlement of those derivatives to close out any related open borrowings of our common stock. In addition, we may loan or pledge securities to a financial institution or other third party that in turn may sell the securities using this prospectus and an applicable prospectus supplement. Such financial institution or other third party may transfer its economic short position to investors in our securities or in connection with a concurrent offering of other securities.

The underwriters, dealers and agents may engage in transactions with us, or perform services for us, in the ordinary course of business for which they receive compensation.

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LEGAL MATTERS

Unless the applicable prospectus supplement indicates otherwise, the validity of the securities in respect of which this prospectus is being delivered will be passed upon by Maynard Nexsen PC. If legal matters in connection with particular offerings of the securities in the future are passed upon by counsel to underwriters, dealers or agents, if any, such counsel will be named in the applicable prospectus supplement.

EXPERTS

The consolidated financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control over Financial Reporting) of ADTRAN Holdings, Inc. incorporated in this prospectus by reference to the Annual Report on Form 10-K for the year ended December 31, 2023 have been so incorporated in reliance on the report (which contains an adverse opinion on the effectiveness of the Company’s internal control over financial reporting) of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

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ADTRAN HOLDINGS, INC.

Common Stock

Preferred Stock

Depositary Shares

Senior Debt Securities

Subordinated Debt Securities

Warrants

Purchase Contracts

Units

PROSPECTUS

    , 2024

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution.

Set forth below are the various expenses, other than underwriting discounts and commissions, to be borne by us in connection with the issuance and distribution of the securities being registered hereby.

Item 15. Indemnification of Directors and Officers.

The following summary is qualified in its entirety by reference to the complete text of any statutes referred to below, as well as the Amended and Restated Certificate of Incorporation (“certificate of incorporation”) and the Second Amended and Restated Bylaws (“bylaws”) of ADTRAN Holdings, Inc. (the “Registrant”).

Section 145(a) of the Delaware General Corporation Law (the “DGCL”) provides, in general, that a corporation shall have the power to indemnify any person who was or is a party or is threatened to be made a party to any threatened, pending or completed action, suit or proceeding, whether civil, criminal, administrative or investigative (other than an action by or in the right of the corporation) by reason of the fact that such person is or was a director or officer, of corporation against expenses (including attorneys’ fees), judgments, fines and amounts paid in settlement actually and reasonably incurred by the person in connection with such action, suit or proceeding if the person acted in good faith and in a manner the person reasonably believed to be in or not opposed to the best interests of the corporation, and, with respect to any criminal action or proceeding, had no reasonable cause to believe the person’s conduct was unlawful.

Section 145(b) of the DGCL provides, in general, that a corporation shall have the power to indemnify any person who was or is a party or is threatened to be made a party to any threatened, pending or completed action or suit by or in the right of the corporation to procure a judgment in its favor because the person is or was a director or officer of the corporation, against any expenses (including attorneys’ fees) actually and reasonably incurred by the person in connection with the defense or settlement of such action or suit if the person acted in good faith and in a manner the person reasonably believed to be in or not opposed to the best interests of the corporation, except that no indemnification shall be made in respect of any claim, issue or matter as to which such person shall have been adjudged to be liable to the corporation unless and only to the extent that the Court of Chancery or the court in which such action or suit was brought shall determine upon application that, despite the adjudication of liability but in view of all the circumstances of the case, such person is fairly and reasonably entitled to be indemnified for such expenses which the Court of Chancery or such other court shall deem proper.

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Under Section 145(c) of the DGCL, present and former directors, and certain present and former officers, who have been successful on the merits or otherwise in defense of any action, suit or proceeding referenced in Section 145(a) or 145(b) of the DGCL, or in defense of any claim, issue or matter therein, are entitled to mandatory indemnification against expenses (including attorneys’ fees) actually and reasonably incurred by such person in connection therewith.

Section 145(e) of the DCGL permits a corporation to pay expenses (including attorneys’ fees) incurred by an officer or director of the corporation in defending any civil, criminal, administrative or investigative action, suit or proceeding in advance of the final disposition of such action, suit or proceeding upon receipt of an undertaking by or on behalf of such director or officer to repay such amount if it shall ultimately be determined that such person is not entitled to be indemnified by the corporation.

Section 145(g) of the DCGL provides, in general, that a corporation shall have the power to purchase and maintain insurance on behalf of any person who is or was a director or officer of the corporation against any liability asserted against the person in any such capacity, or arising out of the person’s status as such, whether or not the corporation would have the power to indemnify the person against such liability under the provisions of the law.

As permitted by the DGCL, the Registrant’s certificate of incorporation provides that (1) the Registrant is required to indemnify each person who was or is made a party or is threatened to be made a party to or is involved in any action, suit or proceeding, whether civil, criminal, administrative or investigative (hereinafter a “proceeding”), by reason of the fact that he or she, or a person of whom he or she is the legal representative, is or was a director or officer of the Registrant or is or was serving at the request of the Registrant as a director or officer of another corporation or of a partnership, joint venture, trust or other enterprise, including service with respect to employee benefit plans, whether the basis of such proceeding is alleged action in an official capacity as a director or officer or in any other capacity while serving as a director or officer, to the fullest extent permitted by the DGCL as it exists or may hereafter be amended (but, in the case of any such amendment, only to the extent that such amendment permits the Registrant to provide broader indemnification rights than said law permitted the Registrant to provide prior to such amendment); provided, however, that with respect to proceedings seeking to enforce rights to indemnification, the Registrant shall indemnify any such person seeking indemnification in connection with a proceeding (or part thereof) initiated by such person only if such proceeding (or part thereof) was authorized by the Board of Directors of the Registrant; (2) it is permitted to indemnify its other employees and agents to the extent to the fullest extent permitted by the DGCL as it exists or may hereafter be amended (but, in the case of any such amendment, only to the extent that such amendment permits the Registrant to provide broader indemnification rights than said law permitted the Registrant to provide prior to such amendment); (3) it is required to advance expenses, as incurred, to its directors and officers in connection with a legal proceeding, provided, however, that, if the DGCL requires it, the payment of such expenses incurred by a director or officer in his or her capacity as a director or officer (and not in any other capacity in which service was or is rendered by such person while a director or officer, including, without limitation, service to an employee benefit plan) in advance of the final disposition of a proceeding shall be made only upon an undertaking by such director or officer to repay all amounts so advanced if it shall ultimately be determined that they are not entitled to be indemnified; and (4) the rights conferred in its certificate of incorporation are not exclusive.

As permitted by the DGCL, the Registrant’s certificate of incorporation includes a provision that eliminates the personal liability of the Registrant’s directors for monetary damages for breach of fiduciary duty as a director, except for liability (1) for any breach of the director’s duty of loyalty to the Registrant or its stockholders; (2) for acts or omissions not in good faith or that involve intentional misconduct or knowing violation of law; (3) under Section 174 of the DGCL (regarding unlawful dividends, stock purchases and redemptions); or (4) for any transaction from which the director derived an improper personal benefit. If the DGCL is subsequently amended to further eliminate or limit the liability of a director then a director of the Registrant, in addition to the circumstances in which a director is not personally liable as set forth in the preceding sentence, shall not be liable to the fullest extent permitted by the amended DGCL. As permitted by the DGCL, the Registrant’s bylaws provide that it is required to indemnify and advance expenses to its officers, directors, employees and agents to the extent permitted by law or its certificate of incorporation or bylaws.

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The Registrant maintains directors’ and officers’ liability insurance covering the directors and officers of the Registrant against claims arising out of the performance of their duties as such.

Item 16. Exhibits.

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Item 17. Undertakings.

(a) The undersigned Registrant hereby undertakes:

(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i) To include any prospectus required by Section 10(a)(3) of the Securities Act of 1933;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than a 20 percent change in the maximum aggregate offering price set forth in the “Calculation of Filing Fee Tables” or “Calculation of Registration Fee” table, as applicable, in the effective registration statement;

(iii) To include any material information with respect to the plan of distribution not previously disclosed in the registration statement or any material change to such information in the registration statement;

provided, however, that paragraphs (a)(1)(i), (a)(l)(ii) and (a)(l)(iii) above do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the Commission by the Registrant pursuant to Section 13 or Section 15(d) of the Securities Exchange Act of 1934 that are incorporated by reference in the registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of the registration statement.

(2) That, for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(4) That, for the purpose of determining liability under the Securities Act of 1933 to any purchaser:

(i) Each prospectus filed by the Registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

(ii) Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5), or (b)(7) as part of a registration statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(l)(i), (vii), or (x) for the purpose of providing the information required by Section 10(a) of the Securities Act of 1933 shall be deemed to be part of and included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration statement to which that prospectus relates, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof. Provided, however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such effective date, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such effective date.

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(5) That, for the purpose of determining liability of the Registrant under the Securities Act of 1933 to any purchaser in the initial distribution of the securities, the undersigned Registrant undertakes that in a primary offering of securities of the undersigned Registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned Registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

(i) Any preliminary prospectus or prospectus of the undersigned Registrant relating to the offering required to be filed pursuant to Rule 424;

(ii) Any free writing prospectus relating to the offering prepared by or on behalf of the undersigned Registrant or used or referred to by the undersigned Registrant;

(iii) The portion of any other free writing prospectus relating to the offering containing material information about the undersigned Registrant or its securities provided by or on behalf of the undersigned Registrant; and

(iv) Any other communication that is an offer in the offering made by the undersigned Registrant to the purchaser.

(b) The undersigned Registrant hereby undertakes that, for purposes of determining any liability under the Securities Act of 1933, each filing of the Registrant’s annual report pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to Section 15(d) of the Securities Exchange Act of 1934) that is incorporated by reference in the registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(c) Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers, and controlling persons of the Registrant pursuant to the foregoing provisions, or otherwise, the Registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Securities Act of 1933 and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a director, officer or controlling person of the Registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

(d) The undersigned Registrant hereby undertakes to file an application for the purpose of determining the eligibility of the trustee to act under subsection (a) of Section 310 of the Trust Indenture Act of 1939 (the “Trust Indenture Act”) in accordance with the rules and regulations prescribed by the Commission under Section 305(b)(2) of the Trust Indenture Act.

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SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Huntsville, State of Alabama on November 18, 2024.

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed by the following persons in the capacities indicated on November 18, 2024.

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Exhibit 5.1

November 18, 2024

ADTRAN Holdings, Inc.

901 Explorer Boulevard

Huntsville, Alabama 35806

Ladies and Gentlemen:

We have acted as counsel to ADTRAN Holdings, Inc., a Delaware corporation (the “Company”), in connection with the Company’s filing of a Registration Statement on Form S-3 (the “Registration Statement”) on this date with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”). The Registration Statement includes a prospectus (the “Prospectus”) that provides it will be supplemented in the future by one or more prospectus supplements (each, a “Prospectus Supplement”) each time that the Company offers and sell securities. The Registration Statement registers under the Securities Act the offering of the following types of securities (the “Securities”) with an aggregate offering price of up to $200,000,000: (i) shares of common stock, par value $0.01 per share, of the Company (“Common Stock”); (ii) shares of preferred stock, par value $0.01 per share, of the Company (“Preferred Stock”); (iii) depositary shares representing fractional shares of Preferred Stock (“Depositary Shares”); (iv) unsecured senior debt securities of the Company (“Senior Debt Securities”); (v) unsecured subordinated debt securities of the Company (“Subordinated Debt Securities” and, together with the Senior Debt Securities, the “Debt Securities”); (vi) warrants to purchase Common Stock, Preferred Stock, Depositary Shares or other securities that are registered in the Registration Statement (“Warrants”); (vii) purchase contracts to purchase Common Stock, Preferred Stock, Depositary Shares, or Debt Securities (“Purchase Contracts”); and (viii) units representing an interest in two or more types of securities that are registered in the Registration Statement (“Units”). The Securities are being registered for offer and sale from time to time on a delayed and continuous basis pursuant to Rule 415 under the Securities Act.

The Senior Debt Securities may be issued pursuant to a senior indenture (the “Senior Indenture”) to be entered into between the Company and a trustee to be named therein, as trustee (the “Senior Trustee”) and duly qualified under the Trust Indenture Act of 1939, as amended (the “Trust Indenture Act”). The Subordinated Debt Securities may be issued pursuant to a subordinated indenture (the “Subordinated Indenture,” and together with the Senior Indenture, the “Indentures,” and each individually, an “Indenture”) to be entered into between the Company and a trustee to be named therein, as trustee (the “Subordinated Trustee” and together with the Senior Trustee, the “Trustees,” and each individually, a “Trustee”) and duly qualified under the Trust Indenture Act. The Warrants may be issued pursuant to a warrant agreement (the “Warrant Agreement”) to be entered into between the Company and a bank or trust company to be named therein, as warrant agent. The Purchase Contracts may be issued pursuant to a purchase contract agreement (the “Purchase Contract Agreement”) to be entered into between the Company and a bank or other third party to be named therein, as purchase contract agent. The Units may be issued pursuant to a Unit Agreement (the “Unit Agreement”) to be entered into between the Company and a bank or trust company to be named therein, as unit agent.

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November 18, 2024

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We have examined and relied upon signed copies of the Registration Statement being filed with the Commission, including the exhibits thereto. We have also examined and relied upon the Amended and Restated Certificate of Incorporation of the Company (as amended or restated from time to time, the “Certificate of Incorporation”), the Amended and Restated Bylaws of the Company (as amended or restated from time to time, the “Bylaws”), and resolutions of the Board of Directors of the Company relating to the filing of the Registration Statement, as provided to us by the Company.

In our examination of the foregoing documents, we have assumed the genuineness of all signatures, the legal capacity of all signatories, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as copies, the authenticity of such original documents, and the completeness and accuracy of the corporate minute books of the Company and all certificates, records, agreements, instruments and documents that we have examined.

We have relied as to certain matters on information obtained from public officials and officers of the Company, and we have assumed (i) the Registration Statement will be effective and will comply with all applicable laws at the time Securities are offered or issued as contemplated by the Registration Statement; (ii) one or more Prospectus Supplements will have been prepared and filed with the Commission describing the Securities offered thereby; (iii) all Securities will be issued and sold in compliance with applicable federal and state securities laws and in the manner stated in the Registration Statement, the Prospectus, and any applicable Prospectus Supplement; (iv) in the case of Debt Securities, (a) the applicable Indenture will be duly authorized, executed and delivered by the applicable Trustee in substantially the form filed as Exhibit 4.4 or Exhibit 4.5 to the Registration Statement, (b) the applicable Trustee will be duly eligible to serve as trustee, and (c) the Debt Securities will be duly authenticated by the Trustee named in the applicable Indenture; (v) any Warrant Agreement, Purchase Contract Agreement or Unit Agreement, as applicable, will be duly authorized, executed and delivered by all parties thereto other than the Company; (vi) a definitive purchase, underwriting or similar agreement with respect to any Securities offered will be duly authorized, executed and delivered by all parties thereto other than the Company; (vii) any Securities issuable upon conversion, exchange or exercise of any Security being offered will be duly authorized, created and, if appropriate, reserved for issuance upon such conversion, exchange or exercise; (viii) with respect to shares of Common Stock offered, there will be sufficient shares of Common Stock authorized under the Certificate of Incorporation and not otherwise reserved for issuance; (ix) with respect to shares of Preferred Stock offered, there will be sufficient shares of Preferred Stock authorized under the Certificate of Incorporation and not otherwise reserved for issuance; (x) with respect to Depositary Shares offered, there will be sufficient shares of Preferred Stock authorized under Certificate of Incorporation and not otherwise reserved for issuance; (xi) if issued in uncertificated form, valid book-entry notations for the issuance of Common Stock, Preferred Stock, or Depositary Shares, as applicable, will have been duly made in the share register of the Company; (xii) at the time of the issuance and sale of the Securities, the Company will be validly existing as a corporation and in good standing under the laws of the State of Delaware; and (xiii) any Warrant Agreement, Purchase Contract Agreement or Unit Agreement will be governed by the laws of the State of New York or Delaware.

We are expressing no opinion herein as to the application of any federal or state law or regulation to the power, authority or competence of any party to any agreement with respect to any of the Securities other than the Company. We have assumed that such agreements are, or will be, the valid and binding obligations of each party thereto other than the Company, and enforceable against each such other party in accordance with their respective terms.

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November 18, 2024

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We have assumed for purposes of our opinions below that no authorization, approval or other action by, and no notice to or filing with, any governmental authority or regulatory body or any other third party is required for the due execution, delivery or performance by the Company, or, if any such authorization, approval, consent, action, notice or filing is required, it will have been duly obtained, taken, given or made and will be in full force and effect. We have also assumed that there will not have occurred, prior to the date of issuance of the Securities, any change in law affecting the validity or enforceability of such Securities and that at the time of the issuance and sale of such Securities, the Board of Directors of the Company (or any committee of such Board of Directors or any person acting pursuant to authority properly delegated to such person by the Board of Directors of the Company or any committee of such Board of Directors) shall not have taken any action to rescind or otherwise reduce its prior authorization of the issuance of such Securities.

Our opinions below are qualified to the extent that they may be subject to or affected by (i) applicable bankruptcy, insolvency, reorganization, receivership, moratorium, usury, fraudulent conveyance, fraudulent transfer or similar laws relating to or affecting the rights or remedies of creditors generally, (ii) duties and standards imposed on creditors and parties to contracts, including, without limitation, requirements of materiality, good faith, reasonableness and fair dealing, (iii) general equitable principles, and (iv) acceleration of the Debt Securities, which may affect the collectability of that portion of the stated principal amount thereof that might be determined to constitute unearned interest thereon. Furthermore, we express no opinion as to the availability of any equitable or specific remedy upon any breach of any of the agreements as to which we are opining herein, or any of the agreements, documents or obligations referred to therein, or to the successful assertion of any equitable defenses, inasmuch as the availability of such remedies or the success of any equitable defenses may be subject to the discretion of a court. We also express no opinion herein as to the laws of any state or jurisdiction other than the state laws of the State of New York and the General Corporation Law of the State of Delaware. We also express no opinion herein with respect to compliance by the Company with the securities or “blue sky” laws of any state or other jurisdiction of the United States or of any foreign jurisdiction. We express no opinion and make no statement herein with respect to the antifraud laws of any jurisdiction.

We note that, as of the date of this opinion letter, a judgment for money in an action based on a Security denominated in a foreign currency or currency unit in a Federal or state court in the United States ordinarily would be enforced in the United States only in United States dollars. The date used to determine the rate of conversion of the foreign currency or currency unit in which a particular Security is denominated into United States dollars will depend upon various factors, including which court renders the judgment. A state court in the State of New York rendering a judgment on such Security would be required under Section 27 of the New York Judiciary Law to render such judgment in the foreign currency in which the Security is denominated, and such judgment would be converted into United States dollars at the exchange rate prevailing on the date of entry of the judgment.

We also express no opinion herein as to any provision of any agreement (i) that may be deemed to or construed to waive any right, defense or counterclaim of the Company, (ii) to the effect that rights and remedies are not exclusive, that every right or remedy is cumulative and may be exercised in addition to or with any other right or remedy and does not preclude recourse to one or more other rights or remedies, (iii) relating to the effect of invalidity or unenforceability of any provision of any agreement on the validity or enforceability of any other provision thereof, (iv) that is in violation of public policy, (v) relating to

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indemnification and contribution with respect to securities law matters, (vi) that provides that the terms of any agreement may not be waived or modified except in writing, (vii) purporting to indemnify any person against his, her or its own negligence or intentional misconduct, (viii) requiring the payment of penalties, consequential damages or liquidated damages or limiting a party’s recovery of certain damages or losses, (ix) purporting to establish evidentiary standards or regarding standards for exercising rights and remedies or (x) relating to choice of law or consent to jurisdiction.

Based upon the foregoing, and subject to the qualifications, assumptions and limitations herein set forth, we are of the opinion that:

1. With respect to shares of Common Stock, when (i) specifically authorized for issuance by proper action of the Board of Directors of the Company or an authorized committee thereof (“Authorizing Resolutions”), (ii) the terms of the issuance and sale of the Common Stock have been duly established in conformity with the Certificate of Incorporation, the Bylaws and Authorizing Resolutions, (iii) the shares of Common Stock have been issued and delivered as contemplated by the Registration Statement, the Prospectus and any applicable Prospectus Supplement in accordance with the applicable underwriting or other purchase agreement or upon conversion or exercise of any Security offered under the Registration Statement against payment therefor, and (iv) the Company has received the consideration provided for in the Authorizing Resolutions and the applicable underwriting agreement or other purchase agreement and such consideration per share is not less than the par value per share of the Common Stock, and, if all the foregoing actions are taken pursuant to the authority granted in the Authorizing Resolutions and so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, the Common Stock will be validly issued, fully paid and non-assessable. The Common Stock covered in the opinion in this paragraph includes any Common Stock of the Company that may be issued as part of the Units or upon exercise or otherwise pursuant to the terms of any other Securities.

2. With respect to shares of Preferred Stock, when (i) specifically authorized for issuance by the Authorizing Resolutions, (ii) the terms of the issuance and sale of the Preferred Stock have been duly established in conformity with the Certificate of Incorporation, the Bylaws and Authorizing Resolutions, (iii) the shares of Preferred Stock have been issued and delivered as contemplated by the Registration Statement, the Prospectus and any applicable Prospectus Supplement in accordance with the applicable underwriting or other purchase agreement or upon conversion or exercise of any Security offered under the Registration Statement against payment therefor, and (iv) the Company has received the consideration provided for in the Authorizing Resolutions and the applicable underwriting agreement or other purchase agreement and such consideration per share is not less than the par value per share of the Preferred Stock, and, if all the foregoing actions are taken pursuant to the authority granted in the Authorizing Resolutions and so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, the Preferred Stock will be validly issued, fully paid and non-assessable. The Preferred Stock covered in the opinion in this paragraph includes any Preferred Stock of the Company that may be represented by Depositary Shares or may be issued as part of the Units or upon exercise or otherwise pursuant to the terms of any other Securities.

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3. With respect to Depositary Shares, when (i) specifically authorized for issuance by the Authorizing Resolutions, (ii) when the terms of the applicable deposit agreement (the “Deposit Agreement”) under which Depositary Shares are to be issued have been duly established and such Deposit Agreement has been duly executed and delivered, (iii) the terms of the Depositary Shares and of their issuance and sale have been duly established in conformity with the Certificate of Incorporation, the Bylaws, the Deposit Agreement and Authorizing Resolutions, (iv) the Certificate of Designation has been duly filed with the Secretary of State of the State of Delaware, (v) the actions with respect to the Preferred Stock underlying such Depositary Shares referenced in paragraph 2 above have been taken and such Preferred stock has been duly deposited with the applicable depositary in accordance with the applicable Deposit Agreement, and (vi) the Depositary Shares have been issued, sold and delivered as contemplated by the Registration Statement, the Prospectus and any applicable Prospectus Supplement, with the related receipts evidencing such Depositary Shares having been duly issued against deposit of the Preferred Stock in accordance with the terms of the applicable Deposit Agreement and the terms of any applicable definitive purchase, underwriting or similar agreement or, if such Depositary Shares are issuable upon exchange or conversion of Securities constituting Debt Securities, the Indenture and applicable officers’ certificate or supplemental indenture therefor, or, if such Depositary Shares are issuable upon exercise of Securities constituting Warrants, the applicable Warrant Agreement therefor, or, if such Depositary Shares are issuable pursuant to Purchase Contracts, the applicable Purchase Contract Agreement therefor, in each case, against payment (or delivery) of the consideration therefor provided for therein, and if all the foregoing actions are taken pursuant to the authority granted in the Authorizing Resolutions and so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, then the depositary receipts evidencing the Depositary Shares will entitle the holders thereof to the rights specified in the Depositary Shares and the applicable Deposit Agreements, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors’ rights and to general equity principles. The Depositary Shares covered in the opinion in this paragraph includes any Depositary Shares of the Company that may be issued as part of the Units or upon exercise or otherwise pursuant to the terms of any other Securities.

4. With respect to the Debt Securities, when (i) specifically authorized for issuance by Authorizing Resolutions, (ii) the applicable Indenture has been duly authorized, executed and delivered by the Company, (iii) the terms of the Debt Securities and of their issuance and sale have been duly established in conformity with the applicable Indenture and the Authorizing Resolutions and assuming such terms and sale do not violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, (iv) such Debt Securities have been duly executed by the Company and authenticated by the applicable Trustee in accordance with the applicable Indenture and delivered and sold as contemplated by the Registration Statement, the Prospectus and any applicable Prospectus Supplement in accordance with the applicable underwriting or other purchase agreement against payment therefor, and (v) the Company has received the consideration provided for in the Authorizing Resolutions and the applicable underwriting agreement or other purchase agreement, and if all the foregoing actions are taken pursuant to the authority granted in the Authorizing Resolutions, such Debt Securities will constitute valid and binding obligations of the Company enforceable against the Company in accordance with their terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors’ rights and to general equity principles. The Debt Securities covered by the opinion in this paragraph include any Debt Securities that may be issued as part of the Units or upon exercise or otherwise pursuant to the terms of any other Securities, as well as any Purchase Contracts or Units that may be issued under the Indentures relating to the Debt Securities.

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November 18, 2024

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5. With respect to the Warrants, when (i) specifically authorized for issuance by the Authorizing Resolutions, (ii) any applicable Warrant Agreement relating to the Warrants has been duly authorized, executed and delivered by the Company, (iii) the terms of the Warrants and of their issuance and sale have been duly established in conformity with any applicable Warrant Agreement and the Authorizing Resolutions, (iv) the Warrants have been duly executed by the Company and countersigned in accordance with any Warrant Agreement and Authorizing Resolutions and issued and delivered as contemplated by the Registration Statement, the Prospectus and any applicable Prospectus Supplement in accordance with the applicable underwriting or other purchase agreement against payment therefor, and (v) the Company has received the consideration provided for in the Authorizing Resolutions and the applicable underwriting agreement or other purchase agreement, and if all the foregoing actions are taken pursuant to the authority granted in the Authorizing Resolutions and so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, such Warrants will constitute valid and binding obligations of the Company enforceable against the Company in accordance with their terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors’ rights and to general equity principles. The Warrants covered by the opinion in this paragraph include any Warrants that may be issued as part of the Units or upon exercise or otherwise pursuant to the terms of any other Securities, but they do not include any Debt Securities.

6. With respect to the Purchase Contracts, when (i) specifically authorized for issuance by the Authorizing Resolutions, (ii) any applicable Purchase Contract Agreement relating to the Purchase Contracts has been duly authorized, executed and delivered by the Company, (iii) the terms of the Purchase Contracts and of their issuance and sale have been duly established in conformity with any applicable Purchase Contract Agreement and the Authorizing Resolutions, (iv) the Purchase Contracts have been duly executed by the Company and countersigned in accordance with any Purchase Contract Agreement and Authorizing Resolutions and issued and delivered as contemplated by the Registration Statement, the Prospectus and any applicable Prospectus Supplement in accordance with the applicable underwriting or other purchase agreement against payment therefor, and (v) the Company has received the consideration provided for in the Authorizing Resolutions and the applicable underwriting agreement or other purchase agreement, and if all the foregoing actions are taken pursuant to the authority granted in the Authorizing Resolutions and so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, such Purchase Contracts will constitute valid and binding obligations of the Company enforceable against the Company in accordance with their terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors’ rights and to general equity principles. The Purchase Contracts covered by the opinion in this paragraph include any Purchase Contracts that may be issued as part of the Units or upon exercise or otherwise pursuant to the terms of any other Securities, but they do not include any Debt Securities.

7. With respect to the Units, when (i) specifically authorized for issuance by the Authorizing Resolutions, (ii) any applicable Unit Agreement has been duly authorized, executed and delivered, (iii) the terms of the Units and of their issuance and sale have been duly established in conformity with any applicable Unit Agreement and the Authorizing Resolutions, (iv) the Units have been duly executed and delivered in accordance with any applicable Unit Agreement and issued and delivered as contemplated by the Registration Statement, the Prospectus and any applicable Prospectus Supplement in

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accordance with the applicable underwriting or other purchase agreement against payment therefor, and (v) the Company has received the consideration provided for in the Authorizing Resolutions and the applicable underwriting agreement or other purchase agreement, and if all the foregoing actions are taken pursuant to the authority granted in the Authorizing Resolutions and so as not to violate any applicable law or result in a default under or breach of any agreement or instrument binding upon the Company and so as to comply with any requirement or restriction imposed by any court or governmental body having jurisdiction over the Company, such Units will constitute valid and binding obligations of the Company enforceable against the Company in accordance with their terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors’ rights and to general equity principles. The Units covered by the opinion in this paragraph include any Units that may be issued upon exercise or otherwise pursuant to the terms of any other Securities, but they do not include any Debt Securities.

To the extent that any opinion herein relates to the enforceability of the choice of New York law and selection of a New York forum or exclusive jurisdiction provisions contained in any instrument or agreement governing the terms of the Securities or in any underwriting or other purchase agreement, the opinions stated herein are subject to the qualification that such enforceability may be subject to, in each case, (i) the exceptions and limitations in Sections 5-1401 and 5-1402 of the New York General Obligations Law and (ii) principles of comity and constitutionality.

Please note that we are opining only as to the matters expressly set forth herein, and no opinion should be inferred as to any other matters. The above opinions are expressed as of the date hereof unless otherwise expressly stated herein and are based upon currently existing statutes, rules, regulations and judicial decisions, and we disclaim any obligation to advise you of any change in any of these sources of law or subsequent legal or factual developments which might affect any matters or opinions set forth herein.

We hereby consent to the filing of this opinion letter with the Commission as an exhibit to the Registration Statement in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Securities Act and to the reference to us under the heading “Legal Matters” in the Prospectus contained therein. In giving such consent, we do not hereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission.

Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in this Registration Statement on Form S-3 of ADTRAN Holdings, Inc. of our report dated March 15, 2024 relating to the financial statements, financial statement schedule, and the effectiveness of internal control over financial reporting, which appears in ADTRAN Holdings, Inc.’s Annual Report on Form 10-K for the year ended December 31, 2023. We also consent to the reference to us under the heading “Experts” in such Registration Statement.

/s/ PricewaterhouseCoopers LLP

Birmingham, Alabama

November 18, 2024

Exhibit 24.1

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, THAT:

The undersigned director of ADTRAN Holdings, Inc. (the “Company”) constitutes and appoints Thomas R. Stanton and Ulrich Dopfer, and each of them severally, his true and lawful attorneys-in-fact and agents with full and several power of substitution, for him and in his name, place and stead, in any and all capacities, to sign the Form S-3 Registration Statement for common stock, preferred stock, depositary shares, senior debt securities, subordinated debt securities, warrants, purchase contracts and units of the Company and any and all amendments and post-effective amendments thereto, and to file the same with all exhibits thereto and all other documents required in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, I have signed this Power of Attorney in the capacity and on the date indicated below.

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, THAT:

The undersigned director of ADTRAN Holdings, Inc. (the “Company”) constitutes and appoints Thomas R. Stanton and Ulrich Dopfer, and each of them severally, his true and lawful attorneys-in-fact and agents with full and several power of substitution, for him and in his name, place and stead, in any and all capacities, to sign the Form S-3 Registration Statement for common stock, preferred stock, depositary shares, senior debt securities, subordinated debt securities, warrants, purchase contracts and units of the Company and any and all amendments and post-effective amendments thereto, and to file the same with all exhibits thereto and all other documents required in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, I have signed this Power of Attorney in the capacity and on the date indicated below.

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, THAT:

The undersigned director of ADTRAN Holdings, Inc. (the “Company”) constitutes and appoints Thomas R. Stanton and Ulrich Dopfer, and each of them severally, his true and lawful attorneys-in-fact and agents with full and several power of substitution, for him and in his name, place and stead, in any and all capacities, to sign the Form S-3 Registration Statement for common stock, preferred stock, depositary shares, senior debt securities, subordinated debt securities, warrants, purchase contracts and units of the Company and any and all amendments and post-effective amendments thereto, and to file the same with all exhibits thereto and all other documents required in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, I have signed this Power of Attorney in the capacity and on the date indicated below.

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, THAT:

The undersigned director of ADTRAN Holdings, Inc. (the “Company”) constitutes and appoints Thomas R. Stanton and Ulrich Dopfer, and each of them severally, her true and lawful attorneys-in-fact and agents with full and several power of substitution, for her and in her name, place and stead, in any and all capacities, to sign the Form S-3 Registration Statement for common stock, preferred stock, depositary shares, senior debt securities, subordinated debt securities, warrants, purchase contracts and units of the Company and any and all amendments and post-effective amendments thereto, and to file the same with all exhibits thereto and all other documents required in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done as fully to all intents and purposes as she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, I have signed this Power of Attorney in the capacity and on the date indicated below.

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, THAT:

The undersigned director of ADTRAN Holdings, Inc. (the “Company”) constitutes and appoints Thomas R. Stanton and Ulrich Dopfer, and each of them severally, his true and lawful attorneys-in-fact and agents with full and several power of substitution, for him and in his name, place and stead, in any and all capacities, to sign the Form S-3 Registration Statement for common stock, preferred stock, depositary shares, senior debt securities, subordinated debt securities, warrants, purchase contracts and units of the Company and any and all amendments and post-effective amendments thereto, and to file the same with all exhibits thereto and all other documents required in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, I have signed this Power of Attorney in the capacity and on the date indicated below.

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, THAT:

The undersigned director of ADTRAN Holdings, Inc. (the “Company”) constitutes and appoints Thomas R. Stanton and Ulrich Dopfer, and each of them severally, his true and lawful attorneys-in-fact and agents with full and several power of substitution, for him and in his name, place and stead, in any and all capacities, to sign the Form S-3 Registration Statement for common stock, preferred stock, depositary shares, senior debt securities, subordinated debt securities, warrants, purchase contracts and units of the Company and any and all amendments and post-effective amendments thereto, and to file the same with all exhibits thereto and all other documents required in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, I have signed this Power of Attorney in the capacity and on the date indicated below.

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, THAT:

The undersigned director of ADTRAN Holdings, Inc. (the “Company”) constitutes and appoints Thomas R. Stanton and Ulrich Dopfer, and each of them severally, her true and lawful attorneys-in-fact and agents with full and several power of substitution, for her and in her name, place and stead, in any and all capacities, to sign the Form S-3 Registration Statement for common stock, preferred stock, depositary shares, senior debt securities, subordinated debt securities, warrants, purchase contracts and units of the Company and any and all amendments and post-effective amendments thereto, and to file the same with all exhibits thereto and all other documents required in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done as fully to all intents and purposes as she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, I have signed this Power of Attorney in the capacity and on the date indicated below.