American Electric Power : 5.15% Senior Notes, Series Q, due 2034

Prospectus Supplement

(To Prospectus dated March 5, 2024)

$450,000,000

AEP Transmission Company, LLC

5.15% Senior Notes, Series Q, due 2034

Interest on the Senior Notes is payable semi-annually on April 1 and October 1 of each year, beginning on October 1, 2024. The Senior Notes will mature on April 1, 2034. We may redeem the Senior Notes either in whole or in part at our option at any time, and from time to time, at the applicable redemption price described below under "Supplemental Description of the Senior Notes-Optional Redemption" on page S-5of this prospectus supplement. The Senior Notes do not have the benefit of a sinking fund.

The Senior Notes are unsecured and rank equally with all of our other unsecured and unsubordinated indebtedness from time to time outstanding and will be effectively subordinated to all of our secured debt, to the extent of the assets securing such debt. We will issue the Senior Notes only in registered form in minimum denominations of $2,000 and integral multiples of $1,000 in excess thereof.

(1)Plus accrued interest, if any, from March 13, 2024.

INVESTING IN THESE NOTES INVOLVES RISKS. SEE THE SECTION ENTITLED "RISK FACTORS" ON PAGE S-3OF THIS PROSPECTUS SUPPLEMENT FOR MORE INFORMATION.

Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of the Senior Notes or determined that this prospectus supplement or the accompanying prospectus is accurate or complete. Any representation to the contrary is a criminal offense.

The Senior Notes are expected to be delivered in book-entry form only through The Depository Trust Company for the accounts of its participants, including Clearstream Banking S.A. and Euroclear Bank SA/NV, on or about March 13, 2024.

Joint Book-Running Managers

Co-Managers

Huntington Capital Markets

C.L. King & Associates

The date of this prospectus supplement is March 11, 2024.

TABLE OF CONTENTS

Prospectus Supplement

ABOUT THIS PROSPECTUS SUPPLEMENT

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering of the Senior Notes and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference in this prospectus supplement and the accompanying prospectus. The second part is the accompanying prospectus, which gives more general information, some of which does not apply to the Senior Notes. If the description of the Senior Notes varies between this prospectus supplement and the accompanying prospectus, you should rely on the information in this prospectus supplement.

You should rely only on the information contained or incorporated by reference in this prospectus supplement and in the accompanying prospectus and in any written communication from the Company or the underwriters specifying the final terms of the offering. We have not, and the underwriters have not, authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. You should assume that the information appearing in this prospectus supplement and the accompanying prospectus and the documents incorporated by reference herein and therein are accurate as of the date on their respective covers. Our business, financial condition, results of operations and prospects may have changed since those respective dates.

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RISK FACTORS

Investing in the Senior Notes involves risk. Please see the risk factors set forth below and in our Annual Report on Form 10-K for the fiscal year ended December 31, 2023, which is incorporated by reference in this prospectus supplement and the accompanying prospectus. Before making an investment decision, you should carefully consider these risks as well as other information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus. The risks and uncertainties described are those presently known to us.

WHERE YOU CAN FIND MORE INFORMATION

The SEC allows us to "incorporate by reference" the information we file with them, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus supplement and the accompanying prospectus, and later information that we file with the SEC will automatically update and supersede this information. We incorporate by reference the documents listed below and any future filings made with the SEC under Sections 13(a), 13(c), 14, or 15(d) of the Securities Exchange Act of 1934 (including any documents filed after the date of the initial registration statement and prior to its effectiveness) until we sell all the notes.

• Annual Report on Form 10-K for the year ended December 31, 2023.

You may request a copy of these filings, at no cost, by writing or telephoning us at the following address:

Investor Relations

American Electric Power Service Corporation 1 Riverside Plaza

Columbus, Ohio 43215 614-716-1000

You should rely only on the information incorporated by reference or provided in the accompanying prospectus, this prospectus supplement, or any supplement and in any written communication from us or any underwriter specifying the final terms of the particular offering. We have not authorized anyone else to provide you with different information. We are not making an offer of these notes in any state where the offer is not permitted. You should not assume that the information in the accompanying prospectus, this prospectus supplement, or any supplement is accurate as of any date other than the date on the front of those documents.

USE OF PROCEEDS

The net proceeds from the sale of the Senior Notes will be used for general corporate purposes relating to our utility business. These purposes may include funding our construction program, repaying advances from affiliates and replenishing working capital. We estimate that our construction costs in 2024 will approximate $1.3 billion. At March 6, 2024, we had approximately $194 million in advances from affiliates outstanding. If we do not use the net proceeds immediately, we may temporarily invest them in short-term,interest-bearing obligations.

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SUPPLEMENTAL DESCRIPTION OF THE SENIOR NOTES

The following description of the particular terms of the Senior Notes supplements and in certain instances replaces the description of the general terms and provisions of the Senior Notes under "Description of the Notes" in the accompanying prospectus. We will issue the Senior Notes under an Indenture, dated as of November 1, 2016, between us and The Bank of New York Mellon Trust Company, N.A., as Trustee (the "Trustee"), as heretofore supplemented and as to be further supplemented as of the issue date for the Senior Notes.

Principal Amount, Maturity, Interest and Payment

The Senior Notes will initially be issued in an aggregate principal amount of $450,000,000. We may at any time and from time to time, without consent of the holders of the Senior Notes, issue additional notes having the same ranking, interest rate, maturity and other terms (other than the date of issuance, issue price and, in some circumstances, the initial interest accrual date and initial interest payment date) as the Senior Notes. These additional notes, together with the Senior Notes, will constitute a single series of notes under the Indenture.

The Senior Notes will mature and become due and payable, together with any accrued and unpaid interest, on April 1, 2034 and will bear interest at the rate of 5.15% per year from March 13, 2024 until April 1, 2034. The Senior Notes are not subject to any sinking fund provision.

Interest on each Senior Note will be payable semi-annually in arrears on each April 1 and October 1 (the "Interest Payment Date") and at redemption, if any, or maturity. The initial Interest Payment Date is October 1, 2024. Each payment of interest shall include interest accrued from March 13, 2024, or the immediately preceding Interest Payment Date, through the day before the next Interest Payment Date. Interest on the Senior Notes will be computed on the basis of a 360-day year consisting of twelve 30-day months.

We will pay interest on the Senior Notes (other than interest payable at redemption, if any, or maturity) in immediately available funds to the registered holders of the Senior Notes as of the Regular Record Date (as defined below) for each Interest Payment Date.

We will pay the principal amount of the Senior Notes and any premium and interest payable at redemption, if any, or at maturity in immediately available funds delivered to the Trustee, and the Trustee will forward such funds to the applicable depositary for payments to its participants for subsequent disbursement to the beneficial owners of the Senior Notes. See - Global Clearance and Settlement Procedures.

The Senior Notes will be issued in minimum denominations of $2,000 and integral multiples of $1,000 in excess thereof.

If any Interest Payment Date, redemption date or the maturity is not a Business Day (as defined below), we will pay all amounts due on the next succeeding Business Day and no additional interest will be paid.

The "Regular Record Date" will be the March 15 or September 15 prior to the relevant Interest Payment Date (whether or not a Business Day).

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"Business Day" means any day that is not a Saturday or Sunday or any other day on which banking institutions in New York City are authorized or required by law or regulation to close.

Optional Redemption

We may redeem the Senior Notes at our option at any time upon no more than 60 and not less than 10 days' notice (either by mail or in compliance with the applicable procedures of DTC).

Prior to January 1, 2034 (three months prior to the maturity date (the "Par Call Date")), we may redeem the Senior Notes at our option, in whole or in part, at any time and from time to time, at a redemption price (expressed as a percentage of principal amount and rounded to three decimal places) equal to the greater of:

• (a) the sum of the present values of the remaining scheduled payments of principal and interest thereon discounted to the redemption date (assuming the Senior Notes matured on the Par Call Date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 20 basis points less (b) interest accrued to the redemption date; and
• 100% of the principal amount of the Senior Notes to be redeemed,
  plus, in each case, accrued and unpaid interest thereon to, but excluding, the redemption date.

On or after the Par Call Date, we may redeem the Senior Notes at our option, in whole or in part, at any time and from time to time, at a redemption price equal to 100% of the principal amount of the Senior Notes to be redeemed, plus accrued and unpaid interest thereon to, but excluding, the redemption date.

For purposes of these redemption provisions, the following term has the following meaning.

"Treasury Rate" means, with respect to any redemption date, the yield determined by us in accordance with the following two paragraphs.

The Treasury Rate shall be determined by us after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the redemption date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as "Selected Interest Rates (Daily)-H.15" (or any successor designation or publication) ("H.15") under the caption "U.S. government securities-Treasury constant maturities-Nominal" (or any successor caption or heading) ("H.15 TCM"). In determining the Treasury Rate, we shall select, as applicable:

• the yield for the Treasury constant maturity on H.15 exactly equal to the period from the redemption date to the Par Call Date (the "Remaining Life"); or
• if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields-one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life-and shall interpolate to the Par Call Date on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or

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• if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this clause, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the redemption date.

If on the third business day preceding the redemption date H.15 TCM is no longer published, we shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such redemption date of the United States Treasury security maturing on, or with a maturity that is closest to the Par Call Date, as applicable. If there is no United States Treasury security maturing on the Par Call Date, but there are two or more United States Treasury securities with a maturity date equally distant from the Par Call Date, one with a maturity date preceding the Par Call Date and one with a maturity date following the Par Call Date, we shall select the United States Treasury security with a maturity date preceding the Par Call Date. If there are two or more United States Treasury securities maturing on the Par Call Date, or two or more United States Treasury securities meeting the criteria of the preceding sentence, we shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time, of such United States Treasury security, and rounded to three decimal places.

Our actions and determinations in determining the redemption price shall be conclusive and binding for all purposes, absent manifest error.

The Trustee shall have no obligation or duty whatsoever to determine, or to verify our calculations of, the redemption price.

Covenants

Consolidation, Merger or Sale

The Company may merge or consolidate with any corporation or sell all or substantially all of its assets as an entirety as long as the successor or purchaser of such assets expressly assumes the payment of principal, and premium, if any, and interest on the Senior Notes.

Limitation on Consolidated Priority Debt

The Company covenants that so long as any of the Senior Notes are outstanding that it will not permit Consolidated Priority Debt to exceed 10% of Consolidated Tangible Net Assets for a period in excess of five consecutive Business Days.

Limitation on Liens

The Company covenants that for so long as any of the Senior Notes are outstanding that it will not create or suffer to exist or permit any of its subsidiaries to create or suffer to exist any Secured Debt, unless, at the same time, the Senior Notes that are outstanding are also secured by such Lien on an equal and ratable basis; provided, however, the foregoing does not limit

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1. Permitted Liens; and
2. Any other Lien not covered in clause (i) as long as immediately after the creation of such Lien the aggregate principal amount of Secured Debt does not exceed 10% of Consolidated Tangible Net Assets.

Covenants Definitions

"Consolidated Priority Debt" means all Priority Debt of the Company and its subsidiaries determined on a consolidated basis eliminating inter-company items.

"Consolidated Tangible Net Assets" means the total of all assets (including revaluations thereof as a result of commercial appraisals, price level restatement or otherwise) appearing on the most recent quarterly or annual, as applicable, consolidated balance sheet of the Company and its consolidated subsidiaries, net of applicable reserves and deductions, but excluding goodwill, trade names, trademarks, patents, unamortized debt discount and all other like intangible assets (which term shall not be construed to include such revaluations), less the aggregate of the consolidated current liabilities of the Company and its consolidated subsidiaries appearing on such balance sheet.

"Debt" means any indebtedness for borrowed money.

"Lien or Liens" means any mortgage, pledge, security interest, or other lien on any utility properties or tangible assets, including, without limitation, the capital stock or comparable equity interests of its subsidiaries, now owned or hereafter acquired by the Company or its subsidiaries.

"Permitted Liens" means

• Liens on property existing at the time of acquisition or construction of such property (or created within one year after completion of such acquisition or construction), whether by purchase, merger, construction or otherwise, or to secure the payment of all or any part of the purchase price or construction cost thereof, including the extension of any Liens to repairs, renewals, replacements, substitutions, betterments, additions, extensions and improvements then or thereafter made on the property subject thereto;
• Any extensions, renewals or replacements (or successive extensions, renewals or replacements), in whole or in part, of Liens permitted by the foregoing clauses;
• The pledge of any bonds or other securities at any time issued under any of the Secured Debt permitted by the above clauses; and
• The creation or existence of leases (operating or capital) made, or existing on property acquired, in the ordinary course of business.

"Priority Debt" means, without duplication, any Debt of the Company's subsidiaries; provided that there shall be excluded from any calculation of Priority Debt, (i) the Debt of any subsidiary owing to the Company or a subsidiary of the Company, and (ii) the Debt of any entity which becomes a subsidiary after the issuance of the Notes and any extension, renewal or refunding thereof; provided that such Debt was not incurred in contemplation of such entity becoming a subsidiary.

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"Secured Debt" means any Debt of the Company or any of its subsidiaries secured by a Lien (other than a Permitted Lien).

Global Clearance and Settlement Procedures

Secondary market trading between Clearstream Banking S.A. ("Clearstream") participants and/or Euroclear Bank SA/NV, as operator of the Euroclear system ("Euroclear") participants will occur in the ordinary way in accordance with the applicable rules and operating procedures of Clearstream and Euroclear, as applicable.

Cross-market transfers between persons holding directly or indirectly through DTC on the one hand, and directly or indirectly through Clearstream participants or Euroclear system participants on the other, will be effected through DTC in accordance with DTC rules on behalf of the relevant European international clearing system by its U.S. depositary; however, such cross-market transactions will require delivery of instructions to the relevant European international clearing system by the counterparty in such system in accordance with its rules and procedures and within its established deadlines (European time). The relevant European international clearing system will, if the transaction meets its settlement requirements, deliver instructions to its U.S. depositary to take action to effect final settlement on its behalf by delivering or receiving securities in DTC, and making or receiving payment in accordance with normal procedures for same-day funds settlement applicable to DTC. Clearstream participants and Euroclear system participants may not deliver instructions directly to their respective U.S. depositaries.

Because of time-zone differences, credits of Notes received in Clearstream or the Euroclear system as a result of a transaction with a DTC participant will be made during subsequent securities settlement processing and dated the Business Day following the DTC settlement date. Such credits or any transactions in such Notes settled during such processing will be reported to the relevant Euroclear system participant or Clearstream participant on such Business Day. Cash received in Clearstream or the Euroclear system as a result of sales of the Notes by or through a Clearstream participant or a Euroclear system participant to a DTC participant will be received with value on the DTC settlement date but will be available in the relevant Clearstream or the Euroclear system cash account only as of the Business Day following settlement in DTC.

Additional Information

For additional important information about the Senior Notes, see "Description of the Notes" in the accompanying prospectus, including: (i) additional information about the terms of the Senior Notes, (ii) general information about the Indenture and the Trustee, and (iii) a description of events of default under the Indenture.

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CERTAIN UNITED STATES FEDERAL INCOME AND ESTATE TAX

CONSEQUENCES TO NON-U.S. HOLDERS

The following is a summary of certain United States federal income and estate tax consequences of the purchase, ownership and disposition of the Senior Notes as of the date hereof. This summary deals only with Senior Notes that are held as capital assets by a non-U.S. holder (as defined below) who acquires the Senior Notes upon original issuance at their initial offering price.

A "non-U.S. holder" means a beneficial owner of the Senior Notes (other than an entity or arrangement treated as a partnership for United States federal income tax purposes) that is not, for United States federal income tax purposes, any of the following:

• an individual citizen or resident of the United States;
• a corporation (or any other entity treated as a corporation for United States federal income tax purposes) created or organized in or under the laws of the United States, any state thereof or the District of Columbia;
• an estate the income of which is subject to United States federal income taxation regardless of its source; or
• a trust if it (1) is subject to the primary supervision of a court within the United States and one or more United States persons have the authority to control all substantial decisions of the trust or (2) has a valid election in effect under applicable United States Treasury regulations to be treated as a United States person.

This summary is based upon provisions of the Internal Revenue Code of 1986, as amended (the "Code"), and regulations, rulings and judicial decisions as of the date hereof. Those authorities may be changed, perhaps retroactively, so as to result in United States federal income and estate tax consequences different from those summarized below. This summary does not address all aspects of United States federal income and estate taxes and does not deal with foreign, state, local or other tax considerations that may be relevant to non-U.S. holders in light of their personal circumstances. In addition, it does not represent a detailed description of the United States federal income and estate tax consequences applicable to you if you are subject to special treatment under the United States federal income tax laws (including if you are a United States expatriate, "controlled foreign corporation," "passive foreign investment company" or a partnership or other pass-through entity for United States federal income tax purposes). We cannot assure you that a change in law will not alter significantly the tax considerations that we describe in this summary.

If a partnership (or other entity or arrangement treated as a partnership for United States federal income tax purposes) holds the Senior Notes, the tax treatment of a partner will generally depend upon the status of the partner and the activities of the partnership. If you are a partner of a partnership holding the Senior Notes, you should consult your tax advisors.

It is anticipated, and this discussion assumes, that the Senior Notes will not be issued with more than a de minimis amount of original issue discount for United States federal income tax purposes.

If you are considering the purchase of Senior Notes, you should consult your own tax advisors concerning the particular United States federal income and estate tax consequences to you of the purchase, ownership and disposition of the Senior Notes, as well as the consequences to you arising under other United States federal tax laws and the laws of any other taxing jurisdiction.

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United States Federal Withholding Tax

Subject to the discussions of backup withholding and FATCA below, United States federal withholding tax will not apply to any payment of interest on the Senior Notes under the "portfolio interest rule," provided that:

• interest paid on the Senior Notes is not effectively connected with your conduct of a trade or business in the United States;
• you do not actually (or constructively) own 10% or more of the total combined voting power of all classes of our voting stock within the meaning of the Code and applicable United States Treasury regulations;
• you are not a controlled foreign corporation that is related to us through stock ownership;
• you are not a bank whose receipt of interest on the Senior Notes is described in section 881(c)(3)(A) of the Code; and
• either (a) you provide your name and address on an Internal Revenue Service ("IRS") Form W-8BEN or IRS Form W-8BEN-E (or other applicable form), and certify, under penalties of perjury, that you are not a United States person as defined under the Code or (b) you hold your Senior Notes through certain foreign intermediaries and satisfy the certification requirements of applicable United States Treasury regulations. Special certification rules apply to non-U.S. holders that are pass-through entities rather than corporations or individuals.

If you cannot satisfy the requirements described above, payments of interest made to you will be subject to a 30% United States federal withholding tax, unless you provide the applicable withholding agent with a properly executed:

• IRS Form W-8BEN or IRS Form W-8BEN-E (or other applicable form) claiming an exemption from or reduction in withholding under the benefit of an applicable income tax treaty; or
• IRS Form W-8ECI (or other applicable form) stating that interest paid on the Senior Notes is not subject to withholding tax because it is effectively connected with your conduct of a trade or business in the United States (as discussed below under "- United States Federal Income Tax").

The 30% United States federal withholding tax generally will not apply to any payment of principal or gain that you realize on the sale, exchange, retirement, redemption or other taxable disposition of a Senior Note.

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