A10 Networks (NYSE: ATEN) sets up universal S-3 shelf for stock, debt and warrants

Rhea-AI Filing Summary

A10 Networks, Inc. has registered a universal shelf on Form S-3 that allows the company and potential selling securityholders to offer, from time to time after effectiveness, a range of securities, including debt securities, common stock, preferred stock, depositary shares and warrants. The aggregate size and exact terms of future offerings will be set in one or more prospectus supplements, which will also specify pricing, detailed terms and the distribution method for each tranche.

The company states that it intends to use net proceeds from any primary offerings as described in the applicable supplements, while it will not receive proceeds from sales by selling securityholders unless otherwise noted. A10 highlights that it is a global provider of secure application and network solutions for enterprises and service providers, and outlines standard New York-law indenture terms for any debt issued, anti-takeover provisions under Delaware law, and broad flexibility to issue up to 500,000,000 authorized shares of common stock and 100,000,000 shares of preferred stock.

Key Figures

Recent common stock price: $30.84 per share Authorized common stock: 500,000,000 shares Authorized preferred stock: 100,000,000 shares +3 more

6 metrics

Recent common stock price $30.84 per share Last reported sale price on the New York Stock Exchange on August 5, 2026

Authorized common stock 500,000,000 shares Authorized under the certificate of incorporation, $0.00001 par value per share

Authorized preferred stock 100,000,000 shares Authorized undesignated preferred stock, $0.00001 par value per share

Section 203 ownership threshold 15% of voting stock Ownership level defining an “interested stockholder” under Delaware General Corporation Law Section 203

Section 203 restriction period 3 years Period during which business combinations with an interested stockholder are restricted

Minimum capital for depositary bank $50 million Required combined capital and surplus for the bank or trust company acting as depositary

Key Terms

shelf registration, depositary shares, original issue discount, covenant defeasance, +2 more

6 terms

shelf registration regulatory

"using a “shelf” registration, or continuous offering, process"

Shelf registration is when a company gets permission ahead of time to sell new stocks or bonds over a period of time instead of all at once. It matters to investors because it lets a company raise money quickly when needed, but it can also change the value of existing shares if many new ones are sold.

depositary shares financial

"Debt Securities Common Stock Preferred Stock Depositary Shares Warrants"

Depositary shares are tradable certificates that represent a fractional piece of a larger security held by a third-party bank, like owning a slice of a single big pie instead of the whole pie. They let companies issue and investors buy smaller, more affordable portions of preferred stock or other instruments; holders usually receive proportional dividends and market pricing similar to ordinary shares, but may have limited voting rights and different liquidity or tax implications, which can affect income and resale value.

original issue discount financial

"be treated as if they were issued with “original issue discount,” or OID"

Original issue discount (OID) is the difference between a debt security’s face value and the lower price at which it is first sold, treated as additional interest that accrues over the life of the instrument. For investors it matters because OID raises the effective yield and changes taxable income and the holding’s cost basis over time — think of buying a $100 voucher for $90 and recognizing the $10 gain as earned interest as the voucher approaches maturity.

covenant defeasance financial

"we may omit to comply with those covenants without creating an event of default under the trust declaration, which we refer to as covenant defeasance"

A covenant defeasance is a legal step where a borrower sets aside cash or high-quality securities in a separate, untouchable account to cover future debt payments, allowing the borrower to remove or neutralize certain loan or bond covenants while the debt remains outstanding. Think of it like putting money in a locked safe to guarantee a mortgage payment so the borrower no longer has to follow some loan rules. It matters to investors because those covenants are protections that limit borrower behavior; defeasance can reduce those protections and change the risk and recovery prospects for creditors and bondholders.

Section 203 of the Delaware General Corporation Law regulatory

"The Company is governed by the provisions of Section 203 of the Delaware General Corporation Law"

depositary receipts financial

"The depositary receipts will evidence the depositary shares issued under the deposit agreement"

A depositary receipt is a certificate issued by a bank that represents ownership of shares in a foreign company and can be bought and sold on a local stock exchange. Think of it as a proxy share held in a safe abroad so investors can trade and receive dividends in their own market and currency, making it easier to access foreign companies while exposing investors to the issuer’s underlying business and cross‑border risks.

Offering Details

shelf

Offering

Offering Type shelf

Use of Proceeds Net proceeds from primary offerings will be used as described in the applicable prospectus supplements; A10 will not receive proceeds from selling securityholder sales unless otherwise stated.

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Available on EDGAR 08/07/2026 - 06:10 AM Accepted by SEC EDGAR 08/06/2026 - 08:06 PM Learn about SEC filing dates

FAQ

What does A10 Networks (ATEN) plan to offer under this Form S-3 shelf?

A10 Networks may offer debt securities, common stock, preferred stock, depositary shares and warrants, either separately or in combination, in one or more future offerings, with specific terms detailed in prospectus supplements.

How will A10 Networks (ATEN) use proceeds from securities sold under this shelf?

A10 Networks intends to use net proceeds from primary offerings as described in the applicable prospectus supplement. It states that it will not receive proceeds from sales by selling securityholders unless a supplement specifies otherwise.

Is this A10 Networks (ATEN) Form S-3 a primary or resale registration?

The shelf registration permits both primary offerings by A10 Networks and resales by selling securityholders. Securities may be sold directly to investors or through underwriters, dealers or agents, as described in future prospectus supplements.

What securities authorization does A10 Networks (ATEN) disclose for its capital stock?

A10 Networks’ certificate of incorporation authorizes 500,000,000 shares of common stock and 100,000,000 shares of preferred stock, each with a par value of $0.00001 per share, giving the board broad flexibility to issue additional equity.

Where is A10 Networks (ATEN) common stock listed and what was the recent price?

A10 Networks’ common stock is listed on the New York Stock Exchange under the symbol “ATEN.” On August 5, 2026, the last reported sale price was $30.84 per share.

What anti-takeover measures affecting A10 Networks (ATEN) investors are described?

A10 Networks is subject to Section 203 of the Delaware General Corporation Law and has charter and bylaw provisions on board vacancies, special meetings and written consents that may delay or discourage attempts to gain control of the company.

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As filed with the Securities and Exchange Commission on August 6, 2026

Registration No. 333-   

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

A10 Networks, Inc.

(Exact name of registrant as specified in its charter)

Delaware		3576		20-1446869
(State or other jurisdiction of incorporation or organization)		(Primary Standard Industrial Classification Code Number)		(I.R.S. Employer Identification Number)

2300 Orchard Parkway

San Jose, California 95131

(408) 325-8668

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

Scott Weber

General Counsel

A10 Networks, Inc.

2300 Orchard Parkway

San Jose, California 95131

(408) 325-8668

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

Copies to:

James J. Masetti

Christina F. Pearson

Pillsbury Winthrop Shaw Pittman LLP

2400 Hanover Street

Palo Alto, California 94304

(650) 233-4500

Approximate date of commencement of proposed sale to the public: From time to time after this registration statement becomes effective, as determined by market conditions and other factors.

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.

Large accelerated filer		☒		Accelerated filer		☐
Non-accelerated filer		☐		Smaller reporting company		☐
				Emerging growth company		☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

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PROSPECTUS

A10 Networks, Inc.

Debt Securities

Common Stock

Preferred Stock

Depositary Shares

Warrants

We or selling securityholders that may be named in a prospectus supplement may, from time to time, offer and sell the securities identified above in one or more offerings. This prospectus describes the general terms of these securities and the general manner in which these securities will be offered. We will provide the specific terms of these securities in supplements to this prospectus. The prospectus supplements will also describe the manner in which these securities will be offered and may also add to, update or change information contained in this prospectus. You should read carefully this prospectus and the applicable prospectus supplement, together with the information incorporated by reference and any related free writing prospectuses, before you invest.

We may, and any selling securityholders may, offer these securities separately or together in any combination for sale directly to investors or through underwriters, dealers or agents. If any underwriters, dealers or agents are involved in the sale of any of these securities, we will set forth their names and describe their compensation in the applicable prospectus supplement.

Our common stock is listed on the New York Stock Exchange under the symbol “ATEN.” On August 5, 2026, the last reported sale price of our common stock on the New York Stock Exchange was $30.84 per share.

Investing in our securities involves risks. See the section entitled “Risk Factors” on page 2 of this prospectus and any similar section contained in the applicable prospectus supplement concerning factors you should consider before investing in our securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is August 6, 2026

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TABLE OF CONTENTS

		Page
About This Prospectus			1
Risk Factors			2
A10 Networks, Inc.			3
Forward-Looking Statements			4
Use of Proceeds			5
Description of Debt Securities			6
Description of Capital Stock			12
Description of Depositary Shares			14
Description of Warrants			17
Forms of Securities			18
Selling Securityholders			20
Plan of Distribution			21
Legal Matters			22
Experts			22
Where You Can Find More Information			22

We have not authorized anyone to provide any information other than that contained or incorporated by reference in this prospectus, any applicable prospectus supplement or any free writing prospectus prepared by or on behalf of us or to which we have referred you. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We are not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information in this prospectus and any prospectus supplement, or incorporated by reference, or in any such free writing prospectus, is accurate only as of the dates of those documents. Our business, financial condition, results of operations and prospects may have changed since those dates.

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or SEC, using a “shelf” registration, or continuous offering, process. Under this shelf registration process, we or selling securityholders may, from time to time, offer and sell separately or together in any combination the securities described in this prospectus in one or more offerings.

This prospectus provides you with a general description of the securities we or any selling securityholder may offer. Each time we sell or any selling securityholder sells securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering and the offered securities. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement or free writing prospectus may also add to, update or change information contained in this prospectus. Any statement that we make in this prospectus will be modified or superseded by any inconsistent statement made by us in a prospectus supplement or free writing prospectus. The registration statement we filed with the Securities and Exchange Commission (the “SEC”) includes exhibits that provide more detail of the matters discussed in this prospectus. You should read carefully this prospectus and the related exhibits filed with the SEC and any prospectus supplement, together with additional information described under the heading “Where You Can Find More Information” and any related free writing prospectuses, before making your investment decision.

Unless the context otherwise requires, references in this prospectus to “A10,” “we,” “us” and “our” refer to A10 Networks, Inc. and its subsidiaries.

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RISK FACTORS

Investing in our securities involves risk. The prospectus supplement relating to a particular offering will contain or incorporate by reference a discussion of risks applicable to an investment in the securities offered. Prior to making a decision about investing in our securities, you should carefully consider the specific factors discussed under the heading “Risk Factors” included in or incorporated by reference into the applicable prospectus supplement and any related free writing prospectus together with all of the other information contained in the prospectus supplement and any related free writing prospectus or appearing in or incorporated by reference into this prospectus, including the risk factors incorporated by reference to our most recent Annual Report on Form 10-K and any subsequent Quarterly Reports on Form 10-Q or Current Reports on Form 8-K. The occurrence of any of these risks might cause you to lose all or part of your investment in the offered securities.

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A10 NETWORKS, INC.

We are a global provider of secure application and network solutions that protect, optimize, and scale business-critical systems across on-premises, hybrid cloud, and edge environments. Our network infrastructure and security products are designed to enable large enterprises, service providers, and cloud platforms worldwide to deliver performance, reliability, and protection against cyber threats, while preparing their networks for the demands of artificial intelligence and next-generation applications. We sell our solutions globally to service providers and enterprises who are looking to modernize and secure their digital infrastructure and application.

A10 Networks, Inc. was incorporated in 2004. Our principal executive offices are located at 2300 Orchard Parkway, San Jose, California 95131, and our telephone number is (408) 325-8668. Our website address is www.a10networks.com. The information contained on, or that can be accessed through, our website is not part of, or incorporated by reference in, this prospectus or any prospectus supplement.

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FORWARD-LOOKING STATEMENTS

When used in this prospectus, the words “expects,” “believes,” “anticipates,” “estimates,” “may,” “could,” “intends,” and similar expressions are intended to identify forward-looking statements. These statements are subject to known and unknown risks and uncertainties that could cause actual results to differ materially from those projected or otherwise implied by the forward-looking statements. These forward-looking statements speak only as of the date of this prospectus. Given these risks and uncertainties, you should not place undue reliance on these forward-looking statements. We will discuss many of these risks and uncertainties in greater detail in any prospectus supplement under the heading “Risk Factors.” Additional cautionary statements or discussions of risks and uncertainties that could affect our results or the achievement of the expectations described in forward-looking statements may also be contained in the documents we incorporate by reference into this prospectus.

These forward-looking statements speak only as of the date of this prospectus. Except as required under the federal securities laws and rules and regulations of the SEC, we expressly disclaim any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in our expectations with regard thereto or any change in events, conditions or circumstances on which any such statement is based. You should, however, review additional disclosures we make in our Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K filed with the SEC.

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USE OF PROCEEDS

We intend to use the net proceeds from the sale of the securities offered by this prospectus as set forth in the applicable prospectus supplement. Unless otherwise stated in the applicable prospectus supplement, we will not receive any of the proceeds from the sale of securities by any selling securityholders.

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DESCRIPTION OF DEBT SECURITIES

The following is a summary of the general terms of the debt securities that we may issue under this prospectus. We will file a prospectus supplement that may contain additional terms when we issue debt securities. The terms presented here, together with the terms in a related prospectus supplement, together with any pricing supplement or term sheet, will be a description of the material terms of the debt securities.

We may issue debt securities either separately, or together with, or upon the conversion or exercise of or in exchange for, other securities described in this prospectus. Debt securities may be our senior, senior subordinated or subordinated obligations and, unless otherwise specified in a supplement to this prospectus, the debt securities will be our direct, unsecured obligations and may be issued in one or more series. Any debt securities that are issued may be exchangeable for or convertible into common stock or any of the other securities that may be issued under this prospectus.

The debt securities we offer will be issued under an indenture between us and a trustee to be named in the applicable indenture, as trustee. The following is a summary of the material provisions of the form of indenture filed as an exhibit to the registration statement of which this prospectus is a part. For each series of debt securities, the applicable prospectus supplement for the series may change and supplement the summary below.

As used in this section only, “we,” “us” and “our” refer to A10 Networks, Inc. excluding our subsidiaries, unless expressly stated or the context otherwise requires.

General Terms of the Indenture

The indenture does not limit the amount of debt securities that we may issue. It provides that we may issue debt securities for any series of debt securities up to the principal amount that we may authorize and they may be in any currency or currency unit that we may designate. Except for the limitations on consolidation, merger and sale of all or substantially all of our assets contained in the indenture, the terms of the indenture do not contain any covenants or other provisions designed to give holders of any debt securities protection against changes in our operations, financial condition or transactions involving us. For each series of debt securities, any restrictive covenants for those debt securities will be described in the applicable prospectus supplement for those debt securities.

We may issue the debt securities issued under the indenture as “discount securities,” which means they may be sold at a discount below their stated principal amount. These debt securities, as well as other debt securities that are not issued at a discount, may, for United States federal income tax purposes, be treated as if they were issued with “original issue discount,” or OID, because of interest payment and other characteristics. Special United States federal income tax considerations applicable to debt securities issued with original issue discount will be described in more detail in any applicable prospectus supplement.

You should refer to the prospectus supplement relating to a particular series of debt securities for a description of the following terms of the debt securities offered by that prospectus supplement and by this prospectus:

• the title of those debt securities;

• any limit on the aggregate principal amount of that series of debt securities;

• the date or dates on which principal and premium, if any, of the debt securities of that series is payable;

• the interest rate or rates (which may be fixed or variable) or the method used to determine the rate or rates, and the date or dates from which interest, if any, on the debt securities of that series will accrue, and the dates when interest is payable and related record dates;

• the right, if any, to extend the interest payment periods and the duration of the extensions;

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• if the amount of payments of principal or interest is to be determined by reference to an index or formula, or based on a coin or currency other than that in which the debt securities are stated to be payable, the manner in which these amounts are determined and the calculation agent, if any, with respect thereto;

• the place or places where and the manner in which principal of, premium, if any, and interest, if any, on the debt securities of that series will be payable and the place or places where those debt securities may be presented for transfer and, if applicable, conversion or exchange;

• the period or periods within which, the price or prices at which and other terms and conditions upon which those debt securities may be redeemed, in whole or in part, at our option or the option of a holder of those securities, if we or a holder is to have that option;

• our obligation or right, if any, to redeem, repay or purchase those debt securities pursuant to any sinking fund or analogous provision or at the option of a holder of those securities, and the terms and conditions upon which the debt securities will be redeemed, repaid or purchased, in whole or in part, pursuant to that obligation;

• the terms, if any, on which the debt securities of that series will be subordinate in right and priority of payment to our other debt;

• the denominations in which those debt securities will be issuable;

• if other than the entire principal amount of the debt securities when issued, the portion of the principal amount payable upon acceleration of maturity as a result of a default on our obligations;

• whether any securities of that series are to be issued in whole or in part in the form of one or more global securities and the depositary for those global securities;

• if the principal of or any premium or interest on the debt securities of that series is to be payable, or is to be payable at our election or the election of a holder of those securities, in securities or other property, the type and amount of those securities or other property, or the manner of determining that amount, and the period or periods within which, and the terms and conditions upon which, any such election may be made;

• the events of default and covenants relating to the debt securities that are in addition to, modify or delete those described in this prospectus;

• conversion or exchange provisions, if any, including conversion or exchange prices or rates and adjustments thereto;

• whether and upon what terms the debt securities may be defeased, if different from the provisions set forth in the indenture;

• the nature and terms of any security for any secured debt securities;

• the terms applicable to any debt securities issued at a discount from their stated principal amount; and

• any other specific terms of any debt securities.

The applicable prospectus supplement will present material United States federal income tax considerations for holders of any debt securities and the securities exchange or quotation system on which any debt securities are to be listed or quoted.

Conversion or Exchange Rights

Debt securities may be convertible into or exchangeable for shares of our equity securities or other securities. The terms and conditions of conversion or exchange will be stated in the applicable prospectus supplement. The terms will include, among others, the following:

• the conversion or exchange price;

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• the conversion or exchange period;

• provisions regarding our ability or the ability of any holder to convert or exchange the debt securities;

• events requiring adjustment to the conversion or exchange price; and

• provisions affecting conversion or exchange in the event of our redemption of the debt securities.

Consolidation, Merger or Sale

We cannot consolidate with or merge with or into, or transfer or lease all or substantially all of our assets to, any person, unless we are the surviving corporation or the successor person is a corporation organized under the laws of the United States, any state of the United States or the District of Columbia and expressly assumes our obligations under the debt securities and the indenture. In addition, we cannot complete such a transaction unless immediately after completing the transaction, no event of default under the indenture, and no event that, after notice or lapse of time or both, would become an event of default under the indenture, has occurred and is continuing. When the successor person has assumed our obligations under the debt securities and the indenture, we will be discharged from all our obligations under the debt securities and the indenture except in limited circumstances.

This covenant would not apply to any recapitalization transaction, a change of control affecting us or a highly leveraged transaction, unless the transaction or change of control were structured to include a merger or consolidation or transfer or lease of all or substantially all of our assets.

Events of Default

The indenture provides that the following will be “events of default” with respect to any series of debt securities:

• failure to pay interest for 30 days after the date payment is due and payable;

• failure to pay principal or premium, if any, on any debt security when due, either at maturity, upon any redemption, by declaration or otherwise and, in the case of technical or administrative difficulties, only if such default persists for a period of more than three business days;

• failure to perform other covenants for 60 days after notice that performance was required;

• certain events in bankruptcy, insolvency or reorganization relating to us; or

• any other event of default provided in the applicable officer’s certificate, resolution of our board of directors or the supplemental indenture under which we issue a series of debt securities.

An event of default for a particular series of debt securities does not necessarily constitute an event of default for any other series of debt securities issued under the indenture. For each series of debt securities, any modifications to the above events of default will be described in the applicable prospectus supplement for those debt securities.

The indenture provides that if an event of default specified in the first, second, third or fifth bullets above occurs and is continuing, either the trustee or the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series may declare the principal amount of all those debt securities (or, in the case of discount securities or indexed securities, that portion of the principal amount as may be specified in the terms of that series) to be due and payable immediately. If an event of default specified in the fourth bullet above occurs and is continuing, then the principal amount of all those debt securities (or, in the case of discount securities or indexed securities, that portion of the principal amount as may be specified in the terms of that series) will be due and payable immediately, without any declaration or other act on the part of the trustee or any holder. In certain cases, holders of a majority in principal amount of the outstanding debt securities of any series may, on behalf of holders of all those debt securities, rescind and annul a declaration of acceleration.

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The indenture imposes limitations on suits brought by holders of debt securities against us. Except for actions for payment of overdue principal or interest, no holder of debt securities of any series may institute any action against us under the indenture unless:

• the holder has previously given to the trustee written notice of default and continuance of such default;

• the holders of at least 25% in principal amount of the outstanding debt securities of the affected series have requested that the trustee institute the action;

• the requesting holders have offered the trustee indemnity for the reasonable expenses and liabilities that may be incurred by bringing the action;

• the trustee has not instituted the action within 60 days of the request and offer of indemnity; and

• the trustee has not received inconsistent direction by the holders of a majority in principal amount of the outstanding debt securities of the affected series.

We will be required to file annually with the trustee a certificate, signed by one of our officers, stating whether or not the officer knows of any default by us in the performance, observance or fulfillment of any condition or covenant of the indenture.

Discharge, Defeasance and Covenant Defeasance

We can discharge or decrease our obligations under the indenture as stated below.

We may discharge obligations to holders of any series of debt securities that have not already been delivered to the trustee for cancellation and that have either become due and payable or are by their terms to become due and payable, or are scheduled for redemption, within one year. We may effect a discharge by irrevocably depositing with the trustee cash or government obligations, as trust funds, in an amount certified to be enough to pay when due, whether at maturity, upon redemption or otherwise, the principal of, and any premium and interest on, the debt securities and any mandatory sinking fund payments.

Unless otherwise provided in the applicable prospectus supplement, we may also discharge any and all of our obligations to holders of any series of debt securities at any time, which we refer to as defeasance. We may also be released from the obligations imposed by any covenants of any outstanding series of debt securities and provisions of the indenture, and we may omit to comply with those covenants without creating an event of default under the trust declaration, which we refer to as covenant defeasance. We may effect defeasance and covenant defeasance only if, among other things:

• we irrevocably deposit with the trustee cash or government obligations denominated in the currency of the debt securities, as trust funds, in an amount certified to be enough to pay at maturity, or upon redemption, the principal (including any mandatory sinking fund payments) of, and any premium and interest on, all outstanding debt securities of the series; and

• we deliver to the trustee an opinion of counsel from a nationally recognized law firm to the effect that the holders of the series of debt securities will not recognize income, gain or loss for U.S. federal income tax purposes as a result of the defeasance or covenant defeasance and that defeasance or covenant defeasance will not otherwise alter the holders’ U.S. federal income tax treatment of principal, and any premium and interest payments on, the series of debt securities.

In the case of a defeasance by us, the opinion we deliver must be based on a ruling of the Internal Revenue Service issued, or a change in U.S. federal income tax law occurring, after the date of the indenture, since such a result would not occur under the U.S. federal income tax laws in effect on that date.

Although we may discharge or decrease our obligations under the indenture as described in the two preceding paragraphs, we may not avoid, among other things, our duty to register the transfer or exchange of any series of debt securities, to replace any temporary, mutilated, destroyed, lost or stolen series of debt securities or to maintain an office or agency in respect of any series of debt securities.

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Modification of the Indenture

The indenture provides that we and the trustee may enter into supplemental indentures without the consent of the holders of debt securities to, among other things:

• evidence the assumption by a successor entity of our obligations;

• add to our covenants for the benefit of the holders of debt securities, or to surrender any rights or power conferred upon us;

• add any additional events of default;

• add to, change or eliminate any of the provisions of the indenture in a manner that will become effective only when there is no outstanding debt security which is entitled to the benefit of the provision as to which the modification would apply;

• add guarantees with respect to or secure any debt securities;

• establish the forms or terms of debt securities of any series;

• evidence and provide for the acceptance of appointment by a successor trustee and add to or change any of the provisions of the indenture as is necessary for the administration of the trusts by more than one trustee;

• cure any ambiguity or correct any inconsistency or defect in the indenture;

• modify, eliminate or add to the provisions of the indenture as shall be necessary to effect the qualification of the indenture under the Trust Indenture Act of 1939 or under any similar federal statute later enacted, and to add to the indenture such other provisions as may be expressly required by the Trust Indenture Act; and

• make any other provisions with respect to matters or questions arising under the indenture that will not be inconsistent with any provision of the indenture as long as the new provisions do not adversely affect the interests of the holders of any outstanding debt securities of any series created prior to the modification.

The indenture also provides that we and the trustee may, with the consent of the holders of not less than a majority in aggregate principal amount of debt securities of each series of debt securities affected by such supplemental indenture then outstanding, add any provisions to, or change in any manner, eliminate or modify in any way the provisions of, the indenture or any supplemental indenture or modify in any manner the rights of the holders of the debt securities. We and the trustee may not, however, without the consent of the holder of each outstanding debt security affected thereby:

• extend the final maturity of any debt security;

• reduce the principal amount or premium, if any;

• reduce the rate or extend the time of payment of interest;

• reduce the amount of the principal of any debt security issued with an original issue discount that is payable upon acceleration;

• change the currency in which the principal, and any premium or interest, is payable;

• impair the right to institute suit for the enforcement of any payment on any debt security when due;

• if applicable, adversely affect the right of a holder to convert or exchange a debt security; or

• reduce the percentage of holders of debt securities of any series whose consent is required for any modification of the indenture or for waivers of compliance with or defaults under the indenture with respect to debt securities of that series.

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The indenture provides that the holders of not less than a majority in aggregate principal amount of the then outstanding debt securities of any series, by notice to the relevant trustee, may on behalf of the holders of the debt securities of that series waive any default and its consequences under the indenture except:

• a default in the payment of, any premium and any interest on, or principal of, any such debt security held by a nonconsenting holder; or

• a default in respect of a covenant or provision of the indenture that cannot be modified or amended without the consent of the holder of each outstanding debt security of each series affected.

Concerning the Trustee

The indenture provides that there may be more than one trustee under the indenture, each for one or more series of debt securities. If there are different trustees for different series of debt securities, each trustee will be a trustee of a trust under the indenture separate and apart from the trust administered by any other trustee under that indenture. Except as otherwise indicated in this prospectus or any prospectus supplement, any action permitted to be taken by a trustee may be taken by such trustee only on the one or more series of debt securities for which it is the trustee under the indenture. Any trustee under the indenture may resign or be removed from one or more series of debt securities. All payments of principal of, and any premium and interest on, and all registration, transfer, exchange, authentication and delivery of, the debt securities of a series will be effected by the trustee for that series at an office designated by the trustee in New York, New York.

The indenture provides that, except during the continuance of an event of default, the trustee will perform only such duties as are specifically set forth in the indenture. During the existence of an event of default, the trustee will exercise those rights and powers vested in it under the indenture and 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.

If the trustee becomes a creditor of ours, the indenture places limitations on the right of the trustee to obtain payment of claims or to realize on property received in respect of any such claim as security or otherwise. The trustee may engage in other transactions. If it acquires any conflicting interest relating to any duties concerning the debt securities, however, it must eliminate the conflict or resign as trustee.

No Individual Liability of Incorporators, Stockholders, Officers or Directors

The indenture provides that no past, present or future director, officer, stockholder or employee of ours, any of our affiliates, or any successor corporation, in their capacity as such, shall have any individual liability for any of our obligations, covenants or agreements under the debt securities or the indenture.

Governing Law

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

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DESCRIPTION OF CAPITAL STOCK

This section describes the general terms and provisions of the shares of our common stock, par value $0.00001 per share, and preferred stock. This description is only a summary. Our amended and restated certificate of incorporation (the “Certificate of Incorporation”) and our amended and restated bylaws (the “Bylaws”) have been filed as exhibits to our periodic reports filed with the SEC, which are incorporated by reference in this prospectus. You should read our Certificate of Incorporation and our Bylaws for additional information before you buy any of our common stock, preferred stock or other securities. See “Where You Can Find More Information.”

Authorized Capital Stock

Under the Certificate of Incorporation, the Company’s authorized capital stock consists of 500,000,000 shares of common stock and 100,000,000 shares of undesignated preferred stock, $0.00001 par value per share.

Common Stock

Common Stock Outstanding. The outstanding shares of common stock are duly authorized, validly issued, fully paid and nonassessable.

Voting Rights. Each holder of common stock is entitled to one vote for each share held of record on the applicable record date on all matters submitted to a vote of stockholders, including the election of directors. Holders of common stock do not have cumulative voting rights in the election of directors.

Dividend Rights. Subject to preferences that may be applicable to any then outstanding preferred stock, holders of common stock are entitled to receive dividends, if any, as may be declared from time to time by the Company’s board of directors out of legally available funds.

Rights upon Liquidation. In the event of a liquidation, dissolution or winding up of the Company, holders of common stock will be entitled to share ratably in the net assets legally available for distribution to stockholders after the payment of all of the Company’s debts and other liabilities and the satisfaction of any liquidation preference granted to the holders of any then outstanding shares of preferred stock.

Other Rights. Holders of common stock have no preemptive, conversion, subscription or other rights, and there are no redemption or sinking fund provisions applicable to common stock. The rights, preferences and privileges of the holders of common stock are subject to and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that the Company may designate and issue in the future.

Listing. Our common stock is listed on the New York Stock Exchange under the symbol “ATEN.”

Transfer Agent and Registrar. The Transfer Agent and Registrar for our common stock is Computershare Trust Company.

Preferred Stock

Under the Certificate of Incorporation, without further stockholder action, the Company’s board of directors is authorized to issue from time to time up to 100,000,000 shares of preferred stock in one or more series and to fix the rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of such series, any or all of which may be greater than the rights of common stock. The issuance of preferred stock by the Company could adversely affect the voting power of holders of common stock and the likelihood that such holders will receive dividend payments and payments upon liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing a change of control of the Company or other corporate action.

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The particular terms of any series of preferred stock, and the transfer agent and registrar for that series, will be described in a prospectus supplement. Any material United States federal income tax consequences and other special considerations with respect to any preferred stock offered under this prospectus will also be described in the applicable prospectus supplement.

Anti-Takeover Effects of Delaware Law, the Certificate of Incorporation and the Bylaws

Certain provisions of Delaware law, the Certificate of Incorporation and the Bylaws may have the effect of delaying, deferring or discouraging another person from acquiring control of the Company. These provisions, which are summarized below, may have the effect of discouraging takeover bids, coercive or otherwise. They are also designed, in part, to encourage persons seeking to acquire control of the Company to negotiate first with the Company’s board of directors.

Delaware Law. The Company is governed by the provisions of Section 203 of the Delaware General Corporation Law, or Section 203. In general, Section 203 prohibits a publicly held Delaware corporation from engaging in a “business combination” with an “interested stockholder” for a period of three years after the date of the transaction in which the person became an interested stockholder, unless the business combination is approved in a prescribed manner. A “business combination” includes mergers, asset sales or other transactions resulting in a financial benefit to the interested stockholder. An “interested stockholder” is a person who, together with affiliates and associates, owns, or within three years did own, 15% or more of the corporation’s outstanding voting stock. These provisions may have the effect of delaying, deferring or preventing a change in control.

Board of Directors Vacancies. The Certificate of Incorporation and Bylaws authorize only the Company’s board of directors to fill vacant directorships, including newly created seats. In addition, the number of directors constituting the Company’s board of directors is permitted to be set only by a resolution adopted by a majority vote of the board of directors. These provisions would prevent a stockholder from increasing the size of the Company’s board of directors and then gaining control of the board of directors by filling the resulting vacancies with its own nominees. This makes it more difficult to change the composition of the Company’s board of directors but promotes continuity of management.

Limits on Ability of Stockholders to Act by Written Consent or Call a Special Meeting. The Certificate of Incorporation provides that stockholders may not take action by written consent. This limit on the ability of stockholders to act by written consent may lengthen the amount of time required to take stockholder actions. As a result, the holders of a majority of the Company’s capital stock would not be able to amend the Bylaws or remove directors without holding a meeting of stockholders called in accordance with the Bylaws. The Bylaws further provide that special meetings of stockholders may be called only by a majority of the Company’s board of directors, the chairperson of the board of directors, the chief executive officer or the president (in the absence of a chief executive officer), thus prohibiting a stockholder from calling a special meeting. These provisions might delay the ability of stockholders to force consideration of a proposal or for stockholders controlling a majority of the Company’s capital stock to take any action, including the removal of directors.

Requirements for Advance Notification of Stockholder Nominations and Proposals. The Bylaws provide advance notice procedures for stockholders seeking to bring business before an annual meeting of stockholders or to nominate candidates for election as directors at an annual meeting of stockholders. The Bylaws also specify certain requirements regarding the form and content of a stockholder’s notice. These provisions might preclude stockholders from bringing matters before an annual meeting of stockholders or from making nominations for directors at an annual meeting of stockholders if the proper procedures are not followed. These provisions may also discourage or deter a potential acquirer from conducting a solicitation of proxies to elect the acquirer’s own slate of directors or otherwise attempting to obtain control of the Company.

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DESCRIPTION OF DEPOSITARY SHARES

The following description of the depositary shares does not purport to be complete and is subject to and qualified in its entirety by the relevant deposit agreement and the depositary receipts with respect to the depositary shares relating to any particular series of preferred stock. You should read these documents as they, and not this description, will define your rights as a holder of depositary shares. Forms of these documents will be filed with the SEC in connection with the offering of depositary shares.

General

If we elect to offer fractional interests in shares of preferred stock, we will provide for the issuance by a depositary to the public of receipts for depositary shares. Each depositary share will represent fractional interests of preferred stock. We will deposit the shares of preferred stock underlying the depositary shares under a deposit agreement between us and a bank or trust company selected by us. The bank or trust company must have its principal office in the United States and a combined capital and surplus of at least $50 million. The depositary receipts will evidence the depositary shares issued under the deposit agreement.

The deposit agreement will contain terms applicable to the holders of depositary shares in addition to the terms stated in the depositary receipts. Each owner of depositary shares will be entitled to all the rights and preferences of the preferred stock underlying the depositary shares in proportion to the applicable fractional interest in the underlying shares of preferred stock. The depositary will issue the depositary receipts to individuals purchasing the fractional interests in shares of the related preferred stock according to the terms of the offering described in a prospectus supplement.

Dividends and Other Distributions

The depositary will distribute all cash dividends or other cash distributions received for the preferred stock to the entitled record holders of depositary shares in proportion to the number of depositary shares that the holder owns on the relevant record date. The depositary will distribute only an amount that can be distributed without attributing to any holder of depositary shares a fraction of one cent. The depositary will add the undistributed balance to and treat it as part of the next sum received by the depositary for distribution to holders of depositary shares.

If there is a non-cash distribution, the depositary will distribute property received by it to the entitled record holders of depositary shares, in proportion, insofar as possible, to the number of depositary shares owned by the holders, unless the depositary determines, after consultation with us, that it is not feasible to make such distribution. If this occurs, the depositary may, with our approval, sell such property and distribute the net proceeds from the sale to the holders. The deposit agreement also will contain provisions relating to how any subscription or similar rights that we may offer to holders of the preferred stock will be available to the holders of the depositary shares.

Conversion, Exchange, Redemption and Liquidation

If any series of preferred stock underlying the depositary shares may be converted or exchanged, each record holder of depositary receipts will have the right or obligation to convert or exchange the depositary shares represented by the depositary receipts.

The terms on which the depositary shares relating to the preferred stock of any series may be redeemed, and any amounts distributable upon our liquidation, dissolution or winding up, will be described in the relevant prospectus supplement.

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Voting

When the depositary receives notice of a meeting at which the holders of the preferred stock are entitled to vote, the depositary will mail the particulars of the meeting to the record holders of the depositary shares. Each record holder of depositary shares on the record date may instruct the depositary on how to vote the shares of preferred stock underlying the holder’s depositary shares. The depositary will try, if practical, to vote the number of shares of preferred stock underlying the depositary shares according to the instructions. We will agree to take all reasonable action requested by the depositary to enable it to vote as instructed.

Amendments

We and the depositary may agree to amend the deposit agreement and the depositary receipt evidencing the depositary shares. Any amendment that (a) imposes or increases certain fees, taxes or other charges payable by the holders of the depositary shares as described in the deposit agreement or that (b) otherwise prejudices any substantial existing right of holders of depositary shares, will not take effect until 30 days after the depositary has mailed notice of the amendment to the record holders of depositary shares. Any holder of depositary shares that continues to hold its shares at the end of the 30-day period will be deemed to have agreed to the amendment.

Termination

We may direct the depositary to terminate the deposit agreement by mailing a notice of termination to holders of depositary shares at least 30 days prior to termination. In addition, a deposit agreement will automatically terminate if:

• the depositary has redeemed all related outstanding depositary shares, or

• we have liquidated, terminated or wound up our business and the depositary has distributed the preferred stock of the relevant series to the holders of the related depositary shares.

Payment of Fees and Expenses

We will pay all fees, charges and expenses of the depositary, including the initial deposit of the preferred stock and any redemption of the preferred stock. Holders of depositary shares will pay transfer and other taxes and governmental charges and any other charges as are stated in the deposit agreement for their accounts.

Resignation and Removal of Depositary

At any time, the depositary may resign by delivering notice to us, and we may remove the depositary. Resignations or removals will take effect upon the appointment of a successor depositary and its acceptance of the appointment. The successor depositary must be appointed within 60 days after delivery of the notice of resignation or removal and must be a bank or trust company having its principal office in the United States and having a combined capital and surplus of at least $50 million.

Reports

The depositary will forward to the holders of depositary shares all reports and communications from us that are delivered to the depositary and that we are required by law, the rules of an applicable securities exchange or our Certificate of Incorporation to furnish to the holders of the preferred stock. Neither we nor the depositary will be liable if the depositary is prevented or delayed by law or any circumstances beyond its control in performing its obligations under the deposit agreement. The deposit agreement limits our obligations and the depositary’s obligations to performance in good faith of the duties stated in the deposit agreement. Neither we nor the depositary will be obligated to prosecute or defend any legal proceeding connected with any depositary shares or

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preferred stock unless the holders of depositary shares requesting us to do so furnish us with satisfactory indemnity. In performing our obligations, we and the depositary may rely upon the written advice of our counsel or accountants, on any information that competent people provide to us and on documents that we believe are genuine.

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DESCRIPTION OF WARRANTS

We may issue warrants for the purchase of debt securities, preferred stock, common stock, depositary shares, or any combination thereof. We may issue warrants independently or together with any other securities offered by any prospectus supplement and may be attached to or separate from the other offered securities. Each series of warrants may be issued under a separate warrant agreement to be entered into by us with a warrant agent. The applicable warrant agent will act solely as our agent in connection with the warrants and will not assume any obligation or relationship of agency or trust for or with any holders or beneficial owners of warrants. Further terms of the warrants and the applicable warrant agreements will be set forth in the applicable prospectus supplement.

The applicable prospectus supplement relating to any particular issue of warrants will describe the terms of the warrants, including, as applicable, the following:

• the title of the warrants;

• the aggregate number of the warrants;

• the price or prices at which the warrants will be issued;

• the designation, terms and number of shares of debt securities, preferred stock or common stock purchasable upon exercise of the warrants;

• the designation and terms of the offered securities, if any, with which the warrants are issued and the number of the warrants issued with each offered security;

• the date, if any, on and after which the warrants and the related debt securities, preferred stock or common stock will be separately transferable;

• the price at which each share of debt securities, preferred stock or common stock purchasable upon exercise of the warrants may be purchased;

• the date on which the right to exercise the warrants shall commence and the date on which that right shall expire;

• the minimum or maximum amount of the warrants which may be exercised at any one time;

• information with respect to book-entry procedures, if any;

• a discussion of certain federal income tax considerations; and

• any other terms of the warrants, including terms, procedures and limitations relating to the exchange and exercise of the warrants.

We and the applicable warrant agent may amend or supplement the warrant agreement for a series of warrants without the consent of the holders of the warrants issued thereunder to effect changes that are not inconsistent with the provisions of the warrants and that do not materially and adversely affect the interests of the holders of the warrants.

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FORMS OF SECURITIES

Each debt security, depositary share and warrant will be represented either by a certificate issued in definitive form to a particular investor or by one or more global securities representing the entire issuance of securities. Unless the applicable prospectus supplement provides otherwise, certificated securities will be issued in definitive form and global securities will be issued in registered form. Definitive securities name you or your nominee as the owner of the security, and in order to transfer or exchange these securities or to receive payments other than interest or other interim payments, you or your nominee must physically deliver the securities to the trustee, registrar, paying agent or other agent, as applicable. Global securities name a depositary or its nominee as the owner of the debt securities, depositary shares or warrants represented by these global securities. The depositary maintains a computerized system that will reflect each investor’s beneficial ownership of the securities through an account maintained by the investor with its broker/dealer, bank, trust company or other representative, as we explain more fully below.

Registered Global Securities

We may issue the registered debt securities, depositary shares and warrants in the form of one or more fully registered global securities that will be deposited with a depositary or its nominee identified in the applicable prospectus supplement and registered in the name of that depositary or nominee. In those cases, one or more registered global securities will be issued in a denomination or aggregate denominations equal to the portion of the aggregate principal or face amount of the securities to be represented by registered global securities. Unless and until it is exchanged in whole for securities in definitive registered form, a registered global security may not be transferred except as a whole by and among the depositary for the registered global security, the nominees of the depositary or any successors of the depositary or those nominees.

If not described below, any specific terms of the depositary arrangement with respect to any securities to be represented by a registered global security will be described in the prospectus supplement relating to those securities. We anticipate that the following provisions will apply to all depositary arrangements.

Ownership of beneficial interests in a registered global security will be limited to persons, called participants, that have accounts with the depositary or persons that may hold interests through participants. Upon the issuance of a registered global security, the depositary will credit, on its book-entry registration and transfer system, the participants’ accounts with the respective principal or face amounts of the securities beneficially owned by the participants. Any underwriters, dealers or agents participating in the distribution of the securities will designate the accounts to be credited. Ownership of beneficial interests in a registered global security will be shown on, and the transfer of ownership interests will be effected only through, records maintained by the depositary, with respect to interests of participants, and on the records of participants, with respect to interests of persons holding through participants. The laws of some states may require that some purchasers of securities take physical delivery of these securities in definitive form. These laws may impair your ability to own, transfer or pledge beneficial interests in registered global securities.

So long as the depositary, or its nominee, is the registered owner of a registered global security, that depositary or its nominee, as the case may be, will be considered the sole owner or holder of the securities represented by the registered global security for all purposes under the applicable indenture, deposit agreement or warrant agreement. Except as described below, owners of beneficial interests in a registered global security:

• will not be entitled to have the securities represented by the registered global security registered in their names;

• will not receive or be entitled to receive physical delivery of the securities in definitive form; and

• will not be considered the owners or holders of the securities under the applicable indenture, deposit agreement or warrant agreement.

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Accordingly, each person owning a beneficial interest in a registered global security must rely on the procedures of the depositary for that registered global security and, if that person is not a participant, on the procedures of the participant through which the person owns its interest, to exercise any rights of a holder under the applicable indenture, deposit agreement or warrant agreement.

We understand that under existing industry practices, if we request any action of holders or if an owner of a beneficial interest in a registered global security desires to give or take any action that a holder is entitled to give or take under the applicable indenture, deposit agreement or warrant agreement, the depositary for the registered global security would authorize the participants holding the relevant beneficial interests to give or take that action, and the participants would authorize beneficial owners owning through them to give or take that action or would otherwise act upon the instructions of beneficial owners holding through them.

We will make payments of principal, premium, if any, and interest, if any, on debt securities, and any payments to holders with respect to depositary shares or warrants, represented by a registered global security registered in the name of a depositary or its nominee to the depositary or its nominee, as the case may be, as the registered owner of the registered global security. None of us, the trustees, the depositaries for depositary shares, the warrant agents, or any other agent of ours, agent of the trustees, agent of such depositaries or agent of the warrant agents will have any responsibility or liability for any aspect of the records relating to, or payments made on account of, beneficial ownership interests in the registered global security or for maintaining, supervising or reviewing any records relating to those beneficial ownership interests.

We expect that the depositary for any of the securities represented by a registered global security, upon receipt of any payment of principal, premium, interest or other distribution of underlying securities or other property to holders on that registered global security, will immediately credit participants’ accounts in amounts proportionate to their respective beneficial interests in that registered global security as shown on the records of the depositary. We also expect that standing customer instructions and customary practices will govern payments by participants to owners of beneficial interests in a registered global security held through the participants, as is now the case with the securities held for the accounts of customers registered in “street name.” We also expect that any of these payments will be the responsibility of those participants.

If the depositary for any of the securities represented by a registered global security is at any time unwilling or unable to continue as depositary or ceases to be a clearing agency registered under the Securities Exchange Act of 1934, or Exchange Act, and a successor depositary registered as a clearing agency under the Exchange Act is not appointed by us within 90 days, we will issue securities in definitive form in exchange for the registered global security that had been held by the depositary. Any securities issued in definitive form in exchange for a registered global security will be registered in the name or names that the depositary gives to the relevant trustee, warrant agent or other relevant agent of ours or theirs. It is expected that the depositary’s instructions will be based upon directions received by the depositary from participants with respect to ownership of beneficial interests in the registered global security that had been held by the depositary.

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SELLING SECURITYHOLDERS

Information about selling securityholders, where applicable, will be set forth in a prospectus supplement, in a post-effective amendment, or in filings we make with the SEC under the Exchange Act that are incorporated by reference.

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PLAN OF DISTRIBUTION

We or any selling securityholder may sell the securities offered by this prospectus from time to time:

• through underwriters or dealers;

• through agents;

• directly to one or more purchasers;

• in short or long transactions; or

• through a combination of any of these methods of sale.

The accompanying prospectus supplement will set forth the terms of the offering and the method of distribution and will identify any firms acting as underwriters, dealers or agents in connection with the offering, including:

• the name or names of any underwriters, dealers or agents;

• the purchase price of the securities and the proceeds to us or any selling securityholder from the sale;

• any underwriting discounts and other items constituting compensation to underwriters, dealers or agents;

• any public offering price;

• any discounts or concessions allowed or reallowed or paid to dealers; and

• any securities exchange or market on which the securities offered in the prospectus supplement may be listed.

Only those underwriters identified in such prospectus supplement are deemed to be underwriters in connection with the securities offered in the prospectus supplement.

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LEGAL MATTERS

The validity of any securities offered by this prospectus will be passed upon for us by Pillsbury Winthrop Shaw Pittman LLP, Palo Alto, California.

EXPERTS

The audited financial statements and management’s assessment of the effectiveness of internal control over financial reporting incorporated by reference in this prospectus and elsewhere in the registration statement have been so incorporated by reference in reliance upon the reports of Grant Thornton LLP, independent registered public accountants, upon the authority of said firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We have filed a registration statement on Form S-3 with the SEC under the Securities Act of 1933. This prospectus is part of the registration statement but the registration statement includes and incorporates by reference additional information and exhibits. We file annual, quarterly and current reports, proxy statements and other information with the SEC. The SEC maintains a website that contains reports, proxy and information statements and other information regarding companies, such as ours, that file documents electronically with the SEC. The address of that website is http://www.sec.gov. The information on the SEC’s website is not part of this prospectus, and any references to this website or any other website are inactive textual references only.

The SEC permits us to “incorporate by reference” the information contained in documents we file with the SEC, which means that we can disclose important information to you by referring you to those documents rather than by including them in this prospectus. Information that is incorporated by reference is considered to be part of this prospectus and you should read it with the same care that you read this prospectus. Later information that we file with the SEC will automatically update and supersede the information that is either contained, or incorporated by reference, in this prospectus, and will be considered to be a part of this prospectus from the date those documents are filed. We have filed with the SEC, and incorporate by reference in this prospectus:

• our Annual Report on Form 10-K for the fiscal year ended December  31, 2025, filed with the SEC on February 25, 2026;

• our Quarterly Reports on Form 10-Q for the quarterly period ended March  31, 2026, filed with the SEC on May 7, 2026, and quarterly period ended June  30, 2026, filed with the SEC on August 6, 2026;

• our Current Reports on Form 8-K filed on February  4, 2026 (to the extent filed under Item 8.01), April  23, 2026, April  28, 2026 (to the extent filed under Item 8.01), May  1, 2026, May  7, 2026, August  5, 2026 (to the extent filed under Items 1.01, 3.02 and 9.01), August 5, 2026 (to the extent filed under Item 8.01) and August 6, 2026;

• the description of our Common Stock contained in Exhibit 4.3 to our Annual Report on Form 10-K filed on March 10, 2020, including any amendment or report filed for the purpose of updating such description.

We also incorporate by reference all additional documents that we file with the SEC under the terms of Section 13(a), 13(c), 14 or 15(d) of the Exchange Act after the filing date of the registration statement of which this prospectus is a part, as well as between the date of this prospectus and the termination of any offering of securities offered by this prospectus. We are not, however, incorporating, in each case, any documents or information that we are deemed to furnish and not file in accordance with SEC rules.

You may request a copy of any or all of the documents incorporated by reference but not delivered with this prospectus, at no cost, by writing or telephoning us at the following address and number: Chief Financial Officer,

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A10 Networks, Inc., 2300 Orchard Parkway, San Jose, California 95131, telephone (408) 325-8668. We will not, however, send exhibits to those documents, unless the exhibits are specifically incorporated by reference in those documents.

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PART II

Information Not Required In Prospectus

Item 14. Other Expenses of Issuance and Distribution.

The following is a statement of estimated expenses in connection with the issuance and distribution of the securities being registered, other than underwriting discounts and commission.

SEC registration fee		$	*
The New York Stock Exchange listing fees*			*	*
Transfer agent and registrar, trustee and depositary fees*			*	*
Printing expenses*			*	*
Legal fees and expenses*			*	*
Accounting fees and expenses*			*	*
Miscellaneous*			*	*
		$		**

* To be deferred pursuant to Rule 456(b) and calculated in connection with the offering of securities under this registration statement pursuant to Rule 457(r).

** Estimated expenses not presently known.

Item 15. Indemnification of Directors and Officers.

Section 145 of the General Corporation Law of the State of Delaware (the “DGCL”) provides for the indemnification of officers, directors, and other corporate agents in terms sufficiently broad to indemnify such persons under certain circumstances for liabilities (including reimbursement for expenses incurred) arising under the Securities Act of 1933. The Certificate of Incorporation and the Bylaws provide for indemnification of the Registrant’s directors, officers, employees and other agents to the maximum extent permitted by the DGCL. The Registrant has also entered into indemnification agreements with its directors and officers that will require the Registrant, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers to the fullest extent not prohibited by law.

Item 16. Exhibits.

Exhibit No.		Description
1.1*		Form of Underwriting Agreement.
4.1		Form of Indenture relating to debt securities.
4.2*		Form of supplemental indenture or other instrument establishing the issuance of one or more series of debt securities (including the form of such debt security).
4.3		Form of common stock certificate of the Registrant (incorporated by reference to Exhibit 4.1 to Amendment No.1 to the Registrant’s Registration Statement on Form S-1/A filed on March 10, 2014).
4.4*		Form of Specimen Preferred Stock Certificate.
4.5*		Form of Deposit Agreement.
4.6*		Form of Depositary Receipt (included in Exhibit 4.5).
4.9*		Form of Warrant Agreement and Warrant Certificate.
5.1		Opinion of Pillsbury Winthrop Shaw Pittman LLP.
23.1		Consent of Pillsbury Winthrop Shaw Pittman LLP (included in Exhibit 5.1).

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Exhibit No.		Description
23.2		Consent of Grant Thornton LLP, Independent Registered Public Accounting Firm.
24.1		Power of Attorney (included on the signature page hereof).
25.1+		Form T-1 Statement of Eligibility of the trustee for the debt securities.
107		Filing Fee Table

* To be filed by amendment or pursuant to a report to be filed pursuant to Section 13 or 15(d) of the Exchange Act, if applicable, and incorporated herein by reference.

+ To be filed by amendment or pursuant to Trust Indenture Act Section 305(b)(2), if applicable.

Item 17. Undertakings.

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 Securities and Exchange Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than a 20% change in the maximum aggregate offering price set forth in the “Calculation of Filing Fees Tables” or “Calculation of Registration Fee” table, as applicable, in the effective registration statement; and

(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 (i), (ii) and (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 Securities and Exchange 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:

(A) 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

(B) 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)(1)(i), (vii), or (x) for the purpose of providing the information required by section 10(a) of the Securities Act of

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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.

(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.

(6) 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 section 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.

(7) 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 in accordance with the rules and regulations prescribed by the Securities and Exchange Commission under section 305(b)(2) of the Trust Indenture Act.

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 any charter provision, by law 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 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

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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 Securities Act of 1933 and will be governed by the final adjudication of such issue.

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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 San Jose, State of California, on August 6, 2026.

A10 Networks, Inc.
By:		/s/ Dhrupad Trivedi
		Dhrupad Trivedi
		President and Chief Executive Officer

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below hereby constitutes and appoints Dhrupad Trivedi, Michelle Caron and Scott Weber, and each of them individually, as his or her true and lawful attorneys-in-fact and agents, with full power of substitution and resubstitution, for him or her and in his or her name, place and stead, in any and all capacities, to sign any and all amendments, including post-effective amendments, to this Registration Statement, and any registration statement relating to the offering covered by this Registration Statement and filed pursuant to Rule 462(b) under the Securities Act of 1933, and to file the same, with exhibits thereto and other documents 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 for all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that the said attorneys-in-fact and agents, or his or her substitute or substitutes may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated.

Signature		Title		Date
/s/ Dhrupad Trivedi Dhrupad Trivedi		President and Chief Executive Officer, Director (Principal Executive Officer)		August 6, 2026
/s/ Michelle Caron Michelle Caron		Chief Financial Officer (Principal Financial Officer and Principal Accounting Officer)		August 6, 2026
/s/ Tor R. Braham Tor R. Braham		Director		August 6, 2026
/s/ Peter Y. Chung Peter Y. Chung		Director		August 6, 2026
/s/ Eric B. Singer Eric B. Singer		Director		August 6, 2026
/s/ Dana Wolf Dana Wolf		Director		August 6, 2026

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