Exhibit 10.1

Execution Version

FIFTH AMENDMENT TO CREDIT AGREEMENT AND WAIVER

FIFTH AMENDMENT TO CREDIT AGREEMENT AND WAIVER (this “Amendment”), dated

as of May 6, 2025, among ADTRAN, INC., a Delaware corporation (the “US Borrower”), ADTRAN NETWORKS SE, a European stock corporation incorporated under the law of the European Union and Germany (“ADVA”), ADTRAN HOLDINGS, INC., a Delaware corporation (“Holdings”), the Lenders (as defined below) party hereto (constituting the Required Lenders) and WELLS FARGO BANK, NATIONAL ASSOCIATION, as administrative agent (the “Administrative Agent”). Unless otherwise indicated, all capitalized terms used herein and not otherwise defined herein shall have the respective meanings provided such terms in the Credit Agreement referred to below.

W I T N E S S E T H:

WHEREAS, the US Borrower, ADVA, Holdings, the lenders party thereto (such lenders party thereto as of the date hereof, the “Lenders”), the Administrative Agent and the other parties thereto have entered into that certain Credit Agreement, dated as of July 18, 2022 (as amended or otherwise modified prior to the date hereof, the “Existing Credit Agreement”; the Existing Credit Agreement, as amended by this Amendment, the “Credit Agreement”);

WHEREAS, the US Borrower has informed the Administrative Agent that the financial statements and Compliance Certificates previously delivered by the Credit Parties with respect to the fiscal quarters ended June 30, 2024 and September 30, 2024 contained certain incorrect information, and the Consolidated Fixed Charge Coverage Ratio for each of those quarters, after giving effect to the correction of such incorrect information, was less than 1.25 to 1.00 (collectively, the “Specified Event”);

WHEREAS as a result of the Specified Event, certain Events of Default have occurred and are continuing, including without limitation (i) Events of Default under Section 10.1(d) of the Credit Agreement as a result of the Credit Parties’ failure to comply with Section 9.12(c) of the Credit Agreement (Consolidated Fixed Charge Coverage Ratio) with respect to the fiscal quarters ended June 30, 2024 and September 30, 2024, (ii) Events of Default under Section 10.1(c) of the Credit Agreement as a result of inaccuracies in the financial statements and Compliance Certificates with respect to the fiscal quarters ended June 30, 2024 and September 30, 2024 previously delivered by the Credit Parties, (iii) Events of Default that have occurred prior to the Amendment Effective Date under Section 10.1(e) of the Credit Agreement as a result of the failure to comply with Section 8.7 of the Credit Agreement as a result of the Specified Event, (iv) Defaults and Events of Default that have occurred prior to the Amendment Effective Date under Section 10.1(d) of the Credit Agreement as a result of the Credit Parties’ failure to comply with the requirement in Section 8.3(a) of the Credit Agreement to deliver a notice with respect to any of the Defaults and Events of Default described in this paragraph, and (v) Defaults and Events of Default that have occurred prior to the Amendment Effective Date under Section 10.1(c) of the Credit Agreement as a result of any representation, warranty, or certification being incorrect or misleading in any respect as a result of any of the Defaults and Events of Default described in this paragraph or the Specified Event (all such Defaults and Events of Default described in this paragraph, collectively, the “Existing Events of Default”);

WHEREAS, (x) the US Borrower intends to make a borrowing of Revolving Credit Loans in an aggregate amount of $24,000,000 on the Amendment Effective Date (the “Fifth Amendment Borrowing”) and (y) the German Borrower intends to make the Fifth Amendment Prepayment (as defined below); and

WHEREAS, the US Borrower and ADVA have requested, and subject to the terms and conditions set forth herein, the Administrative Agent and the Lenders party hereto (the “Consenting Lenders”) have

agreed, to amend the Existing Credit Agreement and waive the Existing Events of Default as more specifically set forth herein.

NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto hereby agree as follows:

Section 1. Amendment to Existing Credit Agreement. Effective as of the Amendment Effective Date (as defined below) and subject to the terms and conditions set forth herein and in reliance upon the representations and warranties of the Credit Parties set forth herein:

“made after the Second Amendment Effective Date by a Foreign Subsidiary Guarantor in any other Adtran Credit Party,”

$350,000,000, the German Borrower Sublimit shall be $50,000,000 and the German Commitment Reduction Threshold shall be $25,000,000.

Section 2. Limited Waiver. Pursuant to Section 12.2 of the Existing Credit Agreement and subject to the terms and conditions set forth herein and in reliance upon the representations and warranties of the Credit Parties set forth herein:

Section 3. Conditions to Effectiveness. This Amendment shall become effective on the date when the following conditions shall have been satisfied or waived (such date, the “Amendment Effective Date”):

For purposes of determining compliance with the conditions specified in this Section 3, each Lender that has signed this Amendment shall be deemed to have consented to, approved or accepted or to be satisfied with, each document or other matter required thereunder to be consented to or approved by or acceptable or satisfactory to a Lender unless the Administrative Agent shall have received notice from such Lender prior to the proposed Amendment Effective Date specifying its objection thereto.

Section 4. Representations and Warranties. To induce the Administrative Agent and the other Lenders to enter into this Amendment, each Credit Party party hereto represents and warrants to the Administrative Agent and the other Lenders on and as of the Amendment Effective Date that, in each case:

Section 5. Reference to and Effect on the Credit Agreement and the Loan Documents. Except as expressly provided herein, the Existing Credit Agreement and the other Loan Documents shall remain unmodified and in full force and effect. This Amendment shall not be deemed (a) to be a waiver of, or

consent to, or a modification or amendment of, any other term or condition of the Existing Credit Agreement or any other Loan Document other than as expressly set forth herein, (b) to prejudice any right or rights which the Administrative Agent or the Lenders may now have or may have in the future under or in connection with the Existing Credit Agreement or the other Loan Documents or any of the instruments or agreements referred to therein, as the same may be amended, restated, supplemented or modified from time to time, or (c) to be a commitment or any other undertaking or expression of any willingness to engage in any further discussion with the Borrowers, any of their Subsidiaries or any other Person with respect to any other waiver, amendment, modification or any other change to the Existing Credit Agreement or the other Loan Documents or any rights or remedies arising in favor of the Lenders or the Administrative Agent, or any of them, under or with respect to any such documents. References in the Existing Credit Agreement to “this Agreement” (and indirect references such as “hereunder”, “hereby”, “herein”, “hereof” or other words of like import) and in any Loan Document to the “Credit Agreement” shall be deemed to be references to the Credit Agreement.

Section 6. Further Assurances. Each Credit Party agrees to, to the extent required by the Loan Documents, make, execute and deliver all such additional and further acts, things, deeds, instruments and documents as the Administrative Agent may reasonably require for the purposes of implementing or effectuating the provisions of this Amendment and the other Loan Documents.

Section 7. Acknowledgement and Reaffirmation. Each Credit Party (a) consents to this Amendment and agrees that the transactions contemplated by this Amendment shall not limit or diminish the obligations of such Person under, or release such Person from any obligations under, any of the Loan Documents to which it is a party (as amended or otherwise modified pursuant to this Amendment), (b) confirms and reaffirms its obligations under each of the Loan Documents to which it is a party (as amended or otherwise modified pursuant to this Amendment), (c) agrees that each of the Loan Documents to which it is a party (as amended or otherwise modified pursuant to this Amendment) remains in full force and effect and is hereby ratified and confirmed, and (d) acknowledges that the Existing Events of Default have occurred and have not, prior to the Amendment Effective Date, been waived.

Section 8. Costs and Expenses. The Borrowers hereby reconfirm their obligations pursuant to Section 12.3(a) of the Credit Agreement to pay and reimburse the Administrative Agent in accordance with the terms thereof.

Section 9. General Release.

claims (including, without limitation, crossclaims, counterclaims, rights of set-off and recoupment), actions, causes of action, suits, debts, accounts, interests, liens, promises, warranties, damages and consequential damages, demands, agreements, bonds, bills, specialties, covenants, controversies, variances, trespasses, judgments, executions, costs, expenses or claims whatsoever, that such Releasor now has or hereafter may have, of whatsoever nature and kind, whether known or unknown, whether now existing or hereafter arising, whether arising at law or in equity (collectively, the “Claims”), against the Administrative Agent (and any sub-agent thereof), each Lender and each Issuing Lender and their respective Related Parties, and their respective successors and assigns (collectively, the “Releasees”), based in whole or in part on facts, whether or not now known, existing on or before the Amendment Effective Date, that relate to, arise out of or otherwise are in connection with any or all of the Loan Documents or transactions contemplated thereby or any actions or omissions in connection therewith. In entering into this Amendment, the Borrowers and each other Credit Party consulted with, and has been represented by, legal counsel and expressly disclaims any reliance on any representations, acts or omissions by any of the Releasees and hereby agrees and acknowledges that the validity and effectiveness of the releases set forth above do not depend in any way on any such representations, acts and/or omissions or the accuracy, completeness or validity thereof.

Section 10. Governing Law. THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK.

Section 11. Counterparts. This Amendment may be executed in any number of counterparts and by the different parties hereto on separate counterparts, each of which counterparts when executed and delivered shall be an original, but all of which shall together constitute one and the same instrument. Delivery by facsimile or electronic transmission of an executed counterpart of a signature page to this Amendment shall be effective as delivery of an original executed counterpart of this Amendment.

Section 12. Entire Agreement. This Amendment is the entire agreement, and supersedes any prior agreements and contemporaneous oral agreements, of the parties concerning its subject matter. This Amendment is a Loan Document and is subject to the terms and conditions of the Credit Agreement.

Section 13. Successors and Assigns. This Amendment shall be binding on and inure to the benefit of the parties hereto and their successors and permitted assigns.

[Signature pages follow]

IN WITNESS WHEREOF, the parties hereto have caused their duly authorized officers to execute and deliver this Amendment as of the date first above written.

ADTRAN, INC., as US Borrower

By: /s/ Timothy Santo

Name: Timothy Santo

Title: President and Chief Financial Officer

ADTRAN NETWORKS SE, as German Borrower

By: /s/ Ulrich Dopfer

Name: Ulrich Dopfer

Title: Member of the executive board

By: /s/ Dr. Christoph Glingener

Name: Dr. Christoph Glingener

Title: Member of the executive board

ADTRAN HOLDINGS, INC., as Holdings

By: /s/ Timothy Santo

Name: Timothy Santo

Title: President and Chief Financial Officer

By: /s/ Thomas Richard Stanton

Name: Thomas Richard Stanton

Title: Chief Executive Officer

ADTRAN, INC.

Fifth Amendment to Credit Agreement Signature Page

WELLS FARGO BANK, NATIONAL ASSOCIATION,

as Administrative Agent, Swingline Lender, an Issuing, an Issuing Lender and a Lender

By: /s/ Patrick McGovern

Name: Patrick McGovern

Title: Senior Vice President

ADTRAN, INC:.

Fifth Amendment to Credit Agreement and Waiver Signature Page

BANK OF AMERICA, N.A., as a Lender

By: /s/ Karen D. Finnerty

Name: Karen D. Finnerty

Title: Senior Vice President

ADTRAN, INC:.

Fifth Amendment to Credit Agreement and Waiver Signature Page

CITIBANK, N.A., as a Lender

By: /s/ Jeremy Fernandez

Name: Jeremy Fernandez

Title: Sr. Vice President

ADTRAN, INC:.

Fifth Amendment to Credit Agreement and Waiver Signature Page

HSBC BANK USA, N.A., as a Lender

By: /s/ Ketak Sampat

Name: Ketak Sampat

Title: Senior Vice President

ADTRAN, INC:.

Fifth Amendment to Credit Agreement and Waiver Signature Page

NORDDEUTSCHE LANDESBANK –

GIROZENTRALE, as a Lender

By: /s/ Freitag

Name: Freitag

Title:

By: /s/ Lena Wendt

Name: Lena Wendt

Title:

ADTRAN, INC:.

Fifth Amendment to Credit Agreement and Waiver Signature Page