424B7

424B7 1 d115604d424b7.htm 424B7 424B7

Filed Pursuant to Rule 424(b)(7)
Registration No. 333-298099

LOGO

PROSPECTUS SUPPLEMENT

To Prospectus Dated August 6, 2026

A10 Networks, Inc.

153,962 Shares of Common Stock

This prospectus supplement relates to the offer and sale from time to time of up to 153,962 of shares (the “Shares”) of common stock, par value $0.00001 per share (“Common Stock”), of A10 Networks, Inc. (“we,” the “Company” or “A10”) by the selling stockholders listed in the section of this prospectus supplement entitled “Selling Stockholders”, or their donees, pledgees, transferees, or other successors in interest, including those who receive any of the shares as a gift, pledge, distribution, redemption, repurchase, cancellation, or other non-sale related transfer (the “Selling Stockholders”). The Shares were issued by us to the Selling Stockholders on June 15, 2026 as partial consideration for our acquisition of all of the outstanding shares of TrojAI Inc., a corporation incorporated under the Canada Business Corporations Act (the “Target”), pursuant to a Share Purchase Agreement, dated as of June 12, 2026, by and among A10 Networks Canada Inc., a corporation incorporated under the Business Corporations Act (Ontario) and a wholly owned subsidiary of the Company (the “Buyer”), the Company, the Target, the shareholders of the Target (including the Selling Stockholders) and Shareholder Representative Services LLC, a Colorado limited liability company, as seller representative (the “Share Purchase Agreement”).

Our registration for resale of the Shares covered by this prospectus supplement does not mean that the Selling Stockholders will offer or sell any of the Shares. The Selling Stockholders may sell the Shares covered by this prospectus supplement in a number of different ways and at varying prices. For additional information on the possible methods of sale that may be used by the Selling Stockholders, you should refer to the section of this prospectus supplement entitled “Plan of Distribution” beginning on page S-10 of this prospectus supplement. We will not receive any of the proceeds from the sale of Shares by the Selling Stockholders. The Selling Stockholders will bear all commissions and discounts, if any, attributable to their sale of Shares.

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

Investing in our Common Stock involves a high degree of risk. You should review carefully the risks and uncertainties described in the section entitled “Risk Factors” contained on page S-3 of this prospectus supplement as well as any other risk factors and information contained in any other documents that are incorporated by reference herein or therein.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement and the accompanying prospectus are truthful or complete. Any representation to the contrary is a criminal offense. The securities are not being offered in any jurisdiction where the offer is not permitted.

The date of this prospectus supplement is August 6, 2026.

TABLE OF CONTENTS

PROSPECTUS SUPPLEMENT


	Page
ABOUT THIS PROSPECTUS SUPPLEMENT		S-1
THE COMPANY		S-2
RISK FACTORS		S-3
DISCLOSURE REGARDING FORWARD-LOOKING STATEMENTS		S-5
USE OF PROCEEDS		S-6
SELLING STOCKHOLDERS		S-7
PLAN OF DISTRIBUTION		S-10
LEGAL MATTERS		S-13
EXPERTS		S-13
WHERE YOU CAN FIND MORE INFORMATION		S-13
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE		S-14

PROSPECTUS


	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

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ABOUT THIS PROSPECTUS SUPPLEMENT

You should rely only on the information contained or incorporated by reference into this prospectus supplement and the accompanying prospectus. We have not authorized anyone to provide you with information different from that contained in this prospectus supplement, the accompanying prospectus and any free writing prospectus prepared by on behalf of us and the selling stockholders or any information incorporated by reference herein and therein. No dealer, salesperson or other person is authorized to give any information or to represent anything not contained in this prospectus supplement or the accompanying prospectus. You should not rely on any unauthorized information or representation.

This prospectus supplement and the accompanying prospectus is an offer to sell only the securities offered hereby and thereby, but only under circumstances and in jurisdictions where it is lawful to do so. You should assume that the information in this prospectus supplement and the accompanying prospectus is accurate only as of the date on the front of the document and that any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus supplement and the accompanying prospectus or any sale of a security.

The distribution of this prospectus supplement and the accompanying prospectus and the issuance of the securities herein and therein may be restricted by law in certain jurisdictions. Persons outside the United States who come into possession of this prospectus supplement and the accompanying prospectus must inform themselves about, and observe any restrictions relating to, the issuance of the securities herein and therein and the distribution of the prospectus supplement and the accompanying prospectus outside the United States. This prospectus supplement and the accompanying prospectus does not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, the securities offered by this prospectus supplement and the accompanying prospectus by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

This prospectus supplement and the accompanying prospectus is part of an automatic shelf registration statement that we filed with the Securities and Exchange Commission (the “SEC”) as a “well-known seasoned issuer” as defined in Rule 405 under the Securities Act of 1933, as amended (the “Securities Act”), utilizing a “shelf” registration process. This document is in two parts that are bound together: (1) this prospectus supplement, which describes the specific details regarding this offering; and (2) the accompanying prospectus, which provides general information, some of which may not apply to this offering. You should read the entire prospectus supplement, as well as the accompanying prospectus and the documents incorporated by reference that are described in the section entitled “Incorporation of Certain Information by Reference.” These documents contain important information you should consider when making your investment decision. Under this shelf registration process, the Selling Stockholders may, from time to time, sell the securities offered by them described in this prospectus supplement through any means described in the section entitled “Plan of Distribution.” Any applicable prospectus supplement may add, update, or change information contained in this prospectus supplement and accompanying prospectus. We will not receive any proceeds from the sale by such Selling Stockholders of the securities offered by them described in this prospectus supplement.

Except as otherwise indicated herein or as the context otherwise requires, references in this prospectus supplement to “A10,” “the Company,” “we,” “us,” “our,” and similar references refer to A10 Networks, Inc. and, unless the context requires otherwise, its subsidiaries.

S-1

THE COMPANY

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 (“AI”) 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. Our service provider customers rely on scalable, efficient, and secure networks to deliver connectivity, cloud and other services that may generate revenue to their customers. Our enterprise customers require secure application delivery, AI-ready infrastructure, and are increasingly concerned about the landscape of cybersecurity threats across their complex networks and emerging AI workloads. Our end-customers operate in a variety of industries, including telecommunications, technology, industrial, retail, financial, gaming, education and government.

For a complete description of our business, financial condition, results of operations and other important information, we refer you to our filings with the SEC that are incorporated by reference in this prospectus supplement and the accompanying prospectus, including our Annual Report on Form 10-K for the year ended December 31, 2025. For instructions on how to find copies of these documents, see the sections entitled “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.”

Our principal executive offices are located at 2300 Orchard Parkway, San Jose, California 95131, and our telephone number at that location is (408) 325-8668. Our Internet address is www.a10networks.com. Except for the documents incorporated by reference in this prospectus supplement and the accompanying prospectus, the information contained on our website is not part of this prospectus supplement or the prospectus supplement and should not be relied upon in connection with making an investment decision.

S-2

RISK FACTORS

Investing in shares of our Common Stock involves a high degree of risk. Before making an investment decision, you should carefully consider the risks described under “Risk Factors” in our most recent Annual Report on Form 10-K, or any updates in our Quarterly Reports on Form 10-Q, together with all of the other information appearing in or incorporated by reference into this prospectus supplement and the accompanying prospectus, before deciding whether to purchase any of the Common Stock being offered. The risks described in these documents are not the only ones we face, but those that we consider to be material. There may be other unknown or unpredictable economic, business, competitive, regulatory or other factors that could have material adverse effects on our future results. Past financial performance may not be a reliable indicator of future performance, and historical trends should not be used to anticipate results or trends in future periods. Our business, financial condition or results of operations could be materially adversely affected by any of these risks. The trading price of shares of our Common Stock could decline due to any of these risks, and you may lose all or part of your investment. Please also read carefully the section entitled “Disclosure Regarding Forward-Looking Statements.”

Risks Relating to our Common Stock

Our stock price may fluctuate significantly.

Technology stocks have historically experienced high levels of volatility. The trading price of our Common Stock has been and is likely to continue to be volatile and subject to fluctuations in response to many factors, some of which are beyond our control and may not be related to our operating performance. These fluctuations could cause you to lose all or part of your investment in our Common Stock. Factors that could cause fluctuations in the trading price of our Common Stock include the following:

•

announcements of new products, services or technologies, commercial relationships, acquisitions or other events by us or our competitors;

•

price and volume fluctuations in the overall stock market from time to time;

•

significant volatility in the market price and trading volume of technology companies in general and of companies in our industry;

•

fluctuations in the trading volume of our shares or the size of our public float;

•

actual or anticipated changes or fluctuations in our results of operations;

•

whether our results of operations meet the expectations of securities analysts or investors;

•

actual or anticipated changes in the expectations of investors or securities analysts;

•

litigation or investigations involving us, our industry, or both;

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regulatory developments in the U.S., foreign countries or both;

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general economic conditions and trends;

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major catastrophic events, including pandemics, acts of terrorism or war, or other events affecting the global economy, and the responses thereto;

•

cyber-attacks and other information or security breaches;

•

sales of large blocks of our Common Stock; or

•

departures of key personnel.

In addition, if the market for technology stocks or the stock market in general experiences a loss of investor confidence, the trading price of our Common Stock could decline for reasons unrelated to our business, results of operations or financial condition. The trading price of our Common Stock might also decline in reaction to events

S-3

that affect other companies in our industry even if these events do not directly affect us. In the past, following periods of volatility in the market price of a company’s securities, securities class action litigation has often been brought against that company. We have experienced securities class action and related derivative litigation and SEC investigations. Future securities litigation, including any related shareholder derivative litigation, or investigations could result in substantial costs and divert our management’s attention and resources from our business. This could have a material adverse effect on our business, results of operations and financial condition

The future sales, or the perception of future sales, of shares by existing stockholders may adversely affect the market price of our Common Stock.

Sales of a substantial number of shares of Common Stock in the public market could occur at any time. If our existing stockholders sell substantial amounts of Common Stock in the public market, or the market perceives that they intend to do so, the market price of our Common Stock could decline. The registration of shares of Common Stock for resale creates the possibility of a significant increase in the supply of our Common Stock in the market. The increased supply, coupled with the potential disparity in purchase prices, may lead to heightened selling pressure, which could negatively affect the public trading price of our Common Stock.

If securities or industry analysts do not publish research or reports about our business, or publish inaccurate or unfavorable research reports about our business, our share price and trading volume could decline.

The market for our Common Stock, to some extent, depends on the research and reports that securities or industry analysts publish about us or our business. If analysts covering us should downgrade our share value or change their opinion of our share value, our share price would likely decline. If analysts should cease coverage of our company or fail to regularly publish reports on us based on current publicly available information, we could lose visibility in the financial markets, which would cause our share price or trading volume to decline.

A reduction in or suspension or elimination of our dividend payments could have a negative effect on our stock price.

On October 28, 2021, we announced that our Board of Directors approved a capital allocation strategy for our stockholders. As part of this strategy, the Board of Directors began declaring quarterly cash dividends. The declaration, amount and timing of any cash dividends are subject to capital availability and determinations by our Board of Directors that cash dividends are in the best interest of our stockholders and are in compliance with all respective laws and our agreements applicable to the declaration and payment of cash dividends. Our ability to pay dividends will depend upon, among other factors, our cash flows from operations, our available capital and potential future capital requirements as well as our results of operations, financial condition and other factors beyond our control that our Board of Directors may deem relevant. A reduction in or suspension or elimination of our dividend payments could have a negative effect on our stock price.

S-4

DISCLOSURE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). The words “believe,” “may,” “will,” “potentially,” “estimate,” “continue,” “anticipate,” “intend,” “could,” “would,” “project,” “plan,” “expect,” “forecasts,” “projections,” and similar expressions that convey uncertainty of future events or outcomes are intended to identify forward-looking statements. These forward-looking statements include, but are not limited to, statements concerning:

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our expectations with respect to demand for our products and services, including AI-ready infrastructure solutions;

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our quarterly cash dividends;

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the volatility of the price of our Common Stock;

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the potential impacts of future sales of our Common Stock by existing stockholders;

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the potential impacts of research and reports that securities or industry analysts publish about us or our business; and

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the risks and uncertainties detailed in the section titled “Risk Factors” in this prospectus supplement, the accompanying prospectus and in our Annual Report on Form 10-K for the year ended December 31, 2025 and our Quarterly Reports on Form 10-Q, which are incorporated by reference herein.

These forward-looking statements are subject to a number of risks, uncertainties, and assumptions, including those described in “Risk Factors” in this prospectus supplement, the accompanying prospectus, as well as in the documents incorporated by reference herein, including our Annual Report on Form 10-K for the year ended December 31, 2025 and any subsequently filed Quarterly Reports on Form 10-Q. We operate in a very competitive and rapidly changing environment, and new risks emerge from time to time. It is not possible for our management to predict all risks, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements we may make. In light of these risks, uncertainties, and assumptions, the forward-looking events and trends discussed in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein may not occur and actual results could differ materially and adversely from those anticipated or implied in the forward-looking statements. Past financial performance may not be a reliable indicator of future performance, and historical trends should not be used to anticipate results or trends in future periods.

You should not rely upon forward-looking statements as predictions of future events. Although we believe that the expectations reflected in the forward-looking statements are reasonable, we cannot guarantee that the future results, levels of activity, performance or events and circumstances reflected in the forward-looking statements will be achieved or occur. Any forward-looking statements made by us in this prospectus supplement, the accompanying prospectus, or in the documents incorporated by reference herein speak only as of the date of the document in which the statement is made, and we do not intend to update these forward-looking statements, except as required by law. Subsequent written and oral forward-looking statements attributable to us or persons acting on our behalf are expressly qualified in their entirety by the cautionary statements contained in this section.

S-5

USE OF PROCEEDS

All of the Shares covered by this prospectus supplement are being offered and sold by the Selling Stockholders. We will not receive any proceeds from the sale of the Shares by the Selling Stockholders.

The Selling Stockholders will pay any underwriting fees, discounts and commissions attributable to the sale of the Shares and any similar expenses it incurs in disposing of the Shares. We will bear all other costs, fees and expenses incurred in effecting the registration of the Shares covered by this prospectus supplement. These may include, without limitation, all registration and filing fees, printing fees and fees and expenses of our legal counsel and accountants in connection with the registration of the Shares covered by this prospectus supplement.

S-6

SELLING STOCKHOLDERS

Unless the context otherwise requires, as used in this prospectus supplement, “Selling Stockholders” includes the Selling Stockholders listed below and donees, pledgees, permitted transferees or other successors-in-interest selling shares received after the date of this prospectus supplement from the Selling Stockholders as a gift, pledge, distribution, redemption, repurchase, cancellation, or other non-sale related transfer.

We have prepared this prospectus supplement to allow the Selling Stockholders or their successors, assignees or other permitted transferees to sell or otherwise dispose of, from time to time, up to 153,962 Shares. On June 15, 2026, we acquired all of the outstanding shares of TrojAI Inc., a corporation incorporated under the Canada Business Corporations Act (the “Target”), from the shareholders of the Target pursuant to a Share Purchase Agreement, dated as of June 12, 2026 (the “Share Purchase Agreement”), by and among the Buyer, the Company, the Target, the shareholders of the Target (including the Selling Stockholders) and Shareholder Representative Services LLC, a Colorado limited liability company, as seller representative. The Shares were issued by the Company in reliance on the exemption from securities registration in Section 4(a)(2) of the Securities Act and/or Regulation D promulgated thereunder.

Pursuant to the Share Purchase Agreement, we agreed to use commercially reasonable efforts to file a shelf registration statement with the SEC covering the resale of the Shares and to keep such registration statement effective for at least one year following the closing of the acquisition.

The Shares to be offered by the Selling Stockholders pursuant to this prospectus supplement are “restricted” securities under applicable federal and state securities laws and are being registered under the Securities Act to give the Selling Stockholders the opportunity to sell the Shares publicly. The registration of the Shares does not require that any of the Shares be offered or sold by the Selling Stockholders.

No estimate can be given as to the amount or percentage of Common Stock that will be held by the Selling Stockholders after any sales of Shares are made pursuant to this prospectus supplement because the Selling Stockholders are not required to sell any of the Shares being registered hereunder. The table below assumes that the Selling Stockholders will sell all of the Shares listed in this prospectus supplement and that they do not purchase additional shares of Common Stock.

Unless otherwise indicated in the footnotes to the table below, the Selling Stockholders have not had any material relationship with us or any of our affiliates within the past three years other than as a security holder.

We have prepared the table below based on written representations and information furnished to us by or on behalf of the Selling Stockholders. Since the date on which the Selling Stockholders provided this information, the Selling Stockholders may have sold, transferred or otherwise disposed of all or a portion of the shares of Common Stock in a transaction exempt from the registration requirements of the Securities Act. Unless otherwise indicated in the footnotes to the table below, we believe that (1) the Selling Stockholders are not broker-dealers or affiliates of a broker-dealer, (2) the Selling Stockholders do not have direct or indirect agreements or understandings with any person to distribute its respective Shares, and (3) the Selling Stockholders have sole voting and investment power with respect to all Shares beneficially owned. To the extent any Selling Stockholder is, or is affiliated with, a broker-dealer, it could be deemed to be, under SEC Staff interpretations, an “underwriter” within the meaning of the Securities Act. Information about the Selling Stockholders may change over time. Any changed information will be set forth in amendments or supplements to this prospectus supplement and the accompanying prospectus, if required.

Unless otherwise indicated, the address of each Selling Stockholder listed in the table below is c/o A10 Networks, Inc., 2300 Orchard Parkway, San Jose, California 95131. The following table sets forth information with respect to the beneficial ownership of our Common Stock held, as of June 15, 2026, by the Selling Stockholders and the number of Shares being offered hereby and information with respect to shares of Common

S-7

Stock to be beneficially owned by the Selling Stockholders after completion of this offering. The percentages in the following table reflect the shares of Common Stock beneficially owned by the Selling Stockholders as a percentage of the total number of shares of Common Stock outstanding as of June 15, 2026.


Name of Beneficial Owner	Shares of Common Stock Beneficially Owned Prior to the Offering⁽¹⁾		Percent of Common Stock Before the Offering		Maximum Number of Shares That may be Offered		Shares of Common Stock Beneficially Owned After the Offering		Percent of Common Stock After the Offering⁽¹⁾⁽²⁾
Stephen Goddard 2023 Family Trust⁽³⁾		26,636		*		26,636		—		—
James Stewart 2023 Family Trust⁽⁴⁾		26,636		*		26,636		—		—
Alteryx, Inc.⁽⁵⁾		1,283		*		1,283		—		—
Atlantic Canada Regional Venture Fund II Limited Partnership⁽⁶⁾		21,592		*		21,592		—		—
Blue Acre Capital Inc.⁽⁷⁾		363		*		363		—		—
Concrete Ventures Fund Limited Partnership⁽⁸⁾		6,985		*		6,985		—		—
Flybridge 2022, L.P.⁽⁹⁾		15,292		*		15,292		—		—
Flybridge Associates 2022, L.P.⁽⁹⁾		752		*		752		—		—
Flying Fish Fund II, LP⁽¹⁰⁾		1,608		*		1,608		—		—
Flying Fish Fund II QP, LP⁽¹⁰⁾		13,494		*		13,494		—		—
NestEarn Inc.⁽¹¹⁾		181		*		181		—		—
New Brunswick Innovation Foundation Inc.⁽¹²⁾		16,044		*		16,044		—		—
Techstars Montréal 2018 L.P.⁽¹³⁾		4,424		*		4,424		—		—
Techstars Ventures 2017, L.P.⁽¹⁴⁾		521		*		521		—		—
Techstars Ventures 2022, L.P.⁽¹⁵⁾		192		*		192		—		—
University of New Brunswick⁽¹⁶⁾		445		*		445		—		—
Lee Weiner⁽¹⁷⁾		16,381		*		16,381		—		—
Stan Petley⁽¹⁸⁾		1,133		*		1,133		—		—

*	Less than 1%

(1)

Based on 72,454,319 shares of Common Stock outstanding as of June 15, 2026. Pursuant to SEC rules, a person is deemed to be the “beneficial owner” of a voting security if such person has (or shares) either investment power or voting power over such security or has (or shares) the right to acquire such security within 60 days by any of a number of means, including upon the exercise of options or warrants, the conversion of convertible securities or the vesting of restricted stock units. A beneficial owner’s percentage ownership is determined by assuming that options, warrants, convertible securities and restricted stock units that are held by the beneficial owner, but not those held by any other person, and which are exercisable or convertible within 60 days, have been exercised or converted.

(2)

Assumes that the Selling Stockholders dispose of all of the Shares and do not acquire beneficial ownership of any additional shares of Common Stock. The registration of these Shares does not necessarily mean that the Selling Stockholders will sell all or any portion of the Shares covered by this prospectus supplement.

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(3)

Stephen Goddard, Susan Bolger, Emily Blanchet are the trustees of the Stephen Goddard 2023 Family Trust (the “SG Trust”) and have voting and investment control of the shares held by the SG Trust. Mr. Goddard served as the Chief Operating Officer and director of the Target and has continued with the Company as an advisor.

(4)	James Stewart is the sole trustee of the James Stewart 2023 Family Trust (the “JS Trust”) and has voting and investment control of the shares held by the JS Trust. Mr. Stewart served as the Chief Technology Officer of the Target and has continued with the Company as Sr. Director, AI Platform.

(5)

Andy MacMillan is the Chief Executive Officer of Alteryx, Inc. (“Alteryx”). Jon Pexton is the Chief Financial Officer of Alteryx. Nali Giliana is the Chief Strategy Officer and Chief of Staff of Alteryx. Mr. MacMillan, Mr. Pexton, and Mr. Giliana have voting and investment power with respect to the shares held by Alteryx. The business address is 3347 Michelson Drive, Suite 400, Irvine, California, 92612.

(6)	Build Ventures II GP Inc. is the general partner of Atlantic Canada Regional Venture Fund II Limited Partnership (“Atlantic Canada”). Build Ventures II GP Inc. has voting and investment control of the shares held by Atlantic Canada. The business address is 957 Young Ave., Halifax NS, B3H2V9.

(7)

Aris Economopoulos is the President of Blue Acre Capital Inc. (“Blue Acre”). Merv D’Souza is the Secretary and Co-Founder of Blue Acre. Meerah Azhar is a director of Blue Acre. Mr. Economopoulos, Mr. D’Souza, and Ms. Azhar have voting and investment control of the shares held by Blue Acre. The business address is 58 Browning Avenue, Toronto, ON, M4K 1V9.

(8)

Concrete Ventures Fund GP Inc. is the general partner of Concrete Ventures Fund Limited Partnership (“Concrete Ventures”). Patrick Hankinson, Partner, has voting and investment control of the shares held by Concrete Ventures. The business address is PO Box 379, Meteghan, Nova Scotia, Canada, B0W 2J0.

(9)

Flybridge 2022 G.P., L.L.C. is the general partner of Flybridge 2022, L.P. and Flybridge Associates 2022, L.P.(each, a “Flybridge 2022 Entity”). Flybridge 2022 G.P., L.L.C. has voting and investment control of the shares held by each Flybridge 2022 Entity. The business address of each Flybridge 2022 Entity is PO Box 369, Norwell, MA 02061.

(10)

Flying Fish Fund II GP, LLC is the general partner of Flying Fish Fund II, LP and Flying Fish Fund II QP, LP (each, a “Flying Fish Entity”). Flying Fish Management LLC is the manager of each Flying Fish Entity. Flying Fish Management LLC has voting and investment control of the shares held by each Flying Fish Entity. The business address of each Flying Fish Entity is 2003 Western Avenue, Suite 510, Seattle, WA 98121.

(11)	Fabian Dsouza, director of NestEarn Inc. (“NestEarn”), has voting and investment control of the shares held by NestEarn. The business address is 788 Stargazer Drive, Mississauga, ON, L5V 0C1.

(12)	The voting directors of New Brunswick Innovation Foundation Inc. (“NBIF”) have voting and investment control of the shares held by NBIF. The business address is 40 Crowther Lane, Suite 110, Fredericton NB E3C 0J1, Canada.

(13)

Techstars Montreal 2018 GP LLC (“Techstars Montreal GP”) is the general partner of Techstars Montréal 2018 L.P. (“Techstars 2018”). Techstars Investments Management LLC is the manager of Techstars Montreal GP. David Cohen, the Chief Executive Officer of Techstars 2018, and Andrew Cleland, the Chief Investment Officer of Techstars 2018, have voting and investment control of the shares held by Techstars 2018. The business address is 228 Park Ave. S., PMB 99696, New York, New York 10003-1502.

(14)

Techstars Ventures GP 2017, LLC is the general partner of Techstars Ventures 2017, L.P. (“Techstars 2017”). David Cohen, the Chief Executive Officer of Techstars 2017, and Andrew Cleland, the Chief Investment Officer of Techstars 2017, have voting and investment control of the shares held by Techstars 2017. The business address is 228 Park Ave. S., PMB 99696, New York, New York 10003-1502.

(15)

Techstars Ventures GP 2022, LLC is the general partner of Techstars Ventures 2022, L.P. (“Techstars 2022”). David Cohen, the Chief Executive Officer of Techstars 2022, and Andrew Cleland, the Chief Investment Officer of Techstars 2022, have voting and investment control of the shares held by Techstars 2022. The business address is 228 Park Ave. S., PMB 99696, New York, New York 10003-1502.

(16)	The business address is PO Box 4400, 8 Bailey Drive, Fredericton, NB E3B 5A3.

(17)	Mr. Weiner served as Chief Executive Officer and a director of the Target and has continued with the Company as Head of AI & Security.

(18)	Mr. Petley served as the Director, Software Engineering of the Target and has continued with the Company as AI Field Technical Lead.

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PLAN OF DISTRIBUTION

We are registering the Shares to permit the resale of the Shares by the holder thereof from time to time after the date of this prospectus supplement. We will not receive any of the proceeds from the sale by the Selling Stockholders of the Shares. We will bear all costs, fees and expenses incurred in effecting the registration of the Shares covered by this prospectus supplement.

Each Selling Stockholder may sell all or a portion of the Shares beneficially owned by it and offered hereby from time to time directly or through one or more underwriters, broker-dealers or agents. If the Shares are sold through underwriters or broker-dealers, such Selling Stockholder will be responsible for underwriting fees, discounts or commissions or agent’s commissions. The Shares may be sold in one or more transactions at fixed prices, at prevailing market prices at the time of the sale, at varying prices determined at the time of sale, or at negotiated prices. The Selling Stockholders will act independently of us in making decisions with respect to the timing, manner and size of each sale of Shares. These sales may be effected in transactions, which may involve cross or block transactions. The Selling Stockholders may use one or more of the following methods when disposing of the Shares or interests therein:

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on any national securities exchange or quotation service on which the securities may be listed or quoted at the time of sale;

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in the over-the-counter market;

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in transactions otherwise than on these exchanges or systems or in the over-the-counter market;

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through the writing or settlement of options or other hedging transactions (including the issuance by the Selling Stockholders of derivative securities), whether such options or such other derivative securities are listed on an options exchange or otherwise;

•

in ordinary brokerage transactions and transactions in which the broker-dealer solicits purchasers;

•

in block trades in which the broker-dealer will attempt to sell the Shares as agent but may position and resell a portion of the block as principal to facilitate the transaction;

•

through purchases by a broker-dealer as principal and resale by the broker-dealer for its account;

•

in an exchange distribution in accordance with the rules of the applicable exchange;

•

in privately negotiated transactions;

•

in short sales;

•

in a public auction;

•

through the distribution of the Shares by such Selling Stockholder to its partners, members or stockholders;

•

through one or more underwritten offerings on a firm commitment or best efforts basis;

•

in sales pursuant to Rule 144 under the Securities Act;

•

whereby broker-dealers may agree with such Selling Stockholder to sell a specified number of such Shares at a stipulated price per share;

•

an offering at other than a fixed price on or through the facilities of any stock exchange on which the shares are then listed or to or through a market maker other than on that stock exchange;

•

in a combination of any such methods of sale; and

•

in any other method permitted pursuant to applicable law.

In addition, a Selling Stockholder that is an entity may elect to make a pro rata in-kind distribution of securities to its members, partners or stockholders pursuant to the registration statement of which this prospectus

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supplement and the accompanying prospectus are a part by delivering a prospectus supplement and the accompanying prospectus with a plan of distribution. Such members, partners or stockholders would thereby receive freely tradeable securities pursuant to the distribution through a registration statement. To the extent a distributee is an affiliate of ours (or to the extent otherwise required by law), we may file a prospectus supplement in order to permit the distributees to use the prospectus supplement to resell the securities acquired in the distribution.

If any Selling Stockholder effects such transactions by selling Shares to or through underwriters, broker-dealers or agents, such underwriters, broker-dealers or agents may receive commissions in the form of discounts, concessions or commissions from such Selling Stockholder or commissions from purchasers of the Shares for whom they may act as agent or to whom they may sell as principal (which discounts, concessions or commissions as to particular underwriters, broker-dealers or agents may be in excess of those customary in the types of transactions involved). In connection with sales of the Shares or otherwise, the Selling Stockholders may enter into hedging transactions with broker-dealers, which may in turn engage in short sales of the Shares in the course of hedging in positions they assume. The Selling Stockholders may also sell the Shares short and deliver Shares covered by this prospectus supplement and the accompanying prospectus to close out short positions and to return borrowed shares of Common Stock in connection with such short sales. The Selling Stockholders may also loan or pledge Shares to broker-dealers that in turn may sell such Shares.

Each Selling Stockholder may pledge, hypothecate or grant a security interest in some or all of the Shares owned by it and, if it defaults in the performance of its secured obligations, the pledgees, secured parties or persons to whom the shares have been hypothecated may offer and sell the Shares from time to time pursuant to this prospectus supplement and the accompanying prospectus or any amendment hereto and thereto under Rule 424(b)(3) or other applicable provision of the Securities Act by amending, if necessary, the list of Selling Stockholders to include the pledgee, transferee or other successors in interest as a Selling Stockholder. Each Selling Stockholder also may transfer and donate the Shares owned by it in other circumstances in which case the transferees, donees, pledgees or other successors in interest will be the selling beneficial owners for purposes of this prospectus supplement.

The Selling Stockholders and any broker-dealer participating in the distribution of the Shares may be deemed to be “underwriters” within the meaning of the Securities Act, and any commission paid, or any discounts or concessions allowed to, any such broker-dealer may be deemed to be underwriting commissions or discounts under the Securities Act. At the time a particular offering of the Shares is made, a prospectus supplement, if required, will be distributed which will set forth the aggregate amount of Shares being offered and the terms of the offering, including the name or names of any broker-dealers or agents, any discounts, commissions and other terms constituting compensation from the Selling Stockholders and any discounts, commissions or concessions allowed or reallowed or paid to broker-dealers. The Selling Stockholders may indemnify any broker-dealer that participates in transactions involving the sale of the Shares against certain liabilities, including liabilities arising under the Securities Act.

The Selling Stockholders or their respective underwriters, broker-dealers, or agents may make sales of the Shares that are deemed to be an at-the-market offering as defined in Rule 415 of the Securities Act, which includes sales of such Shares made directly on or through any stock exchange on which the Shares are listed, the existing trading market for the shares, or in the over-the-counter market or otherwise.

We may indemnify, in certain circumstances, the Selling Stockholders against certain liabilities to which they may become subject in connection with the sale of the Shares offered by them pursuant to this prospectus supplement, including liabilities arising under the Securities Act. Each of the Selling Stockholders may indemnify us in certain circumstances against certain liabilities to which we may become subject in connection with the sale of such Shares, including liabilities arising under the Securities Act. We and the Selling Stockholders may agree to indemnify underwriters, dealers and agents who participate in the distribution of the Shares offered pursuant to this prospectus supplement and the accompanying prospectus against certain liabilities

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to which they may become subject in connection with the sale of such Shares, including liabilities arising under the Securities Act. We have also agreed that if the indemnification described above is held by a court or government agency of competent jurisdiction to be unavailable to any indemnified party or is insufficient to hold them harmless in respect of any losses, then each such indemnifying party, in lieu of indemnifying such indemnified party, shall contribute to the amount paid or payable by such indemnified party as a result of such loss in such proportion as is appropriate to reflect the relative fault of the indemnifying party on the one hand and of such indemnified party on the other in connection with the statements or omissions that resulted in such losses, as well as any other relevant equitable considerations.

Under the securities laws of some states of the United States, the Shares may be sold in such states only through registered or licensed brokers or dealers. In addition, in some states of the United States, the Shares may not be sold unless such Shares have been registered or qualified for sale in such state or an exemption from registration or qualification is available and is complied with.

The aggregate proceeds to the Selling Stockholders from the sale of the Shares offered will be the purchase price of the Shares less discounts or commissions, if any. The Selling Stockholders reserve the right to accept and, together with its agents from time to time, to reject, in whole or in part, any proposed purchase of Shares to be made directly or through agents. There can be no assurance that the Selling Stockholders will sell any or all of the Shares registered hereunder.

The Selling Stockholders and any other person participating in such distribution will be subject to applicable provisions of the Exchange Act and the rules and regulations thereunder, including, without limitation, Regulation M of the Exchange Act, which may limit the timing of purchases and sales of any of the Shares by the Selling Stockholders and any other participating person. Regulation M may also restrict the ability of any person engaged in the distribution of the Shares to engage in market-making activities with respect to the shares of Common Stock. All of the foregoing may affect the marketability of the Shares and the ability of any person or entity to engage in market-making activities with respect to the shares of Common Stock.

We will pay all expenses of the registration of the Shares pursuant to the Share Purchase Agreement, including, without limitation, SEC filing fees and expenses of compliance with state securities or “Blue Sky” laws; provided, however, that the Selling Stockholders will pay all underwriting fees, discounts or commissions attributable to the sale of the Shares and any legal fees and expenses of counsel to the Selling Stockholders. We may be indemnified by the Selling Stockholders against certain liabilities, including certain liabilities under the Securities Act or the Exchange Act, that may arise from any written information furnished to us by the Selling Stockholders specifically for use in this prospectus supplement.

Once sold under the registration statement, of which this prospectus supplement and the accompanying prospectus form a part, the Shares will be freely tradable in the hands of persons, other than our affiliates.

In connection with offerings of securities under the registration statement of which this prospectus supplement and accompanying prospectus form a part and in compliance with applicable law, underwriters, brokers or dealers may engage in transactions that stabilize or maintain the market price of the securities at levels above those that might otherwise prevail in the open market. Specifically, underwriters, brokers or dealers may over-allot in connection with offerings, creating a short position in the securities for their own accounts. For the purpose of covering a syndicate short position or stabilizing the price of the securities, the underwriters, brokers or dealers may place bids for the securities or effect purchases of the securities in the open market. Finally, the underwriters may impose a penalty whereby selling concessions allowed to syndicate members or other brokers or dealers for distribution of the securities in offerings may be reclaimed by the syndicate if the syndicate repurchases previously distributed securities in transactions to cover short positions, in stabilization transactions or otherwise. These activities may stabilize, maintain or otherwise affect the market price of the securities, which may be higher than the price that might otherwise prevail in the open market, and, if commenced, may be discontinued at any time. These transactions may be effected on or through any stock exchange on which the shares are listed, the existing trading market for the shares, or in the over-the-counter market or otherwise.

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LEGAL MATTERS

Unless otherwise indicated, the validity of the Shares offered by this prospectus supplement will be passed upon for us by Pillsbury Winthrop Shaw Pittman LLP, Palo Alto, California.

EXPERTS

The consolidated financial statements of A10 Networks, Inc. appearing in A10 Networks, Inc.’s Annual Report on Form 10-K for the fiscal year ended December 31, 2025 have been audited by Grant Thornton LLP, San Jose, California, independent registered public accounting firm, as set forth in their report thereon, included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such reports given on the authority of such firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We have filed a registration statement on Form S-3, including exhibits, under the Securities Act, with respect to the securities offered by this prospectus supplement. This prospectus supplement and the accompanying prospectus are part of the registration statement, but the registration statement includes and incorporates by reference additional information an exhibits. This prospectus supplement and the accompanying prospectus do not contain all of the information set forth in the registration statement and its exhibits and schedules, portions of which have been omitted as permitted by the rules and regulations of the SEC. For further information pertaining to us and our securities, you should refer to the registration statement of which this prospectus supplement is a part and the exhibits to such registration statement. The descriptions in this prospectus supplement and the accompanying prospectus of the provisions of documents filed as exhibits to this prospectus supplement and the accompanying prospectus are only summaries of those documents’ material terms. You can read copies of such documents, along with copies of reports, proxy statements and other information filed by us with the SEC at the SEC’s website at http://www.sec.gov.

We are subject to the informational requirements of the Exchange Act and are required to file annual, quarterly and current reports, proxy statements and other information with the SEC. Any information we file with the SEC, including the documents incorporated by reference into this prospectus supplement and the accompanying prospectus, is also available on the SEC’s website at www.sec.gov. We also make these documents publicly available, free of charge, on our website at www.a10networks.com as soon as reasonably practicable after filing such documents with the SEC. The information contained in, or that can be accessed through, our website is not part of this prospectus supplement or the accompanying prospectus.

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INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information into this prospectus supplement and the accompanying prospectus, which means that we can disclose important information to you by referring you to another document filed separately with the SEC. The documents incorporated by reference into this prospectus supplement and the accompanying prospectus contain important information that you should read about us. Because we are incorporating by reference future filings with the SEC, this prospectus supplement and the accompanying prospectus are continually updated and those future filings may modify or supersede some of the information included or incorporated in this prospectus supplement and the accompanying prospectus. This means that you must look at all of the SEC filings that we incorporate by reference to determine if any of the statements in this prospectus supplement, the accompanying prospectus or in any document previously incorporated by reference herein or therein have been modified or superseded. This prospectus supplement and the accompanying prospectus incorporate by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (other than information deemed furnished and not filed in accordance with SEC rules, including Items 2.02 and 7.01 of Form 8-K) until the offering of the securities offered hereby is terminated or completed:

The following documents are incorporated by reference into this prospectus supplement and the accompanying 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 the 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, April 23, 2026, April 28, 2026, May 1, 2026, May 7, 2026, August 5, 2026, August 5, 2026 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.

All documents subsequently filed by us (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items unless such Form 8-K expressly provides to the contrary) with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, including those made after the date of the initial filing of the registration statement of which this prospectus supplement forms a part and prior to effectiveness of such registration statement, are deemed to be incorporated by reference into this prospectus supplement and the accompanying prospectus. Such future filings will become a part of this prospectus supplement and the accompanying prospectus from the respective dates that such documents are filed with the SEC.

Any statement contained herein or in a document incorporated or deemed to be incorporated by reference herein shall be deemed to be modified or superseded for purposes hereof to the extent that such statement contained herein or in any other subsequently filed document, which is also incorporated or deemed to be incorporated herein, modifies or supersedes such statement. Any such statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement or the accompanying prospectus.

The documents incorporated by reference into this prospectus supplement and the accompanying prospectus are also available on our corporate website at www.a10networks.com under the heading “Investor Relations.” Information contained on, or that can be accessed through, our website is not part of this prospectus supplement or the accompanying prospectus, and you should not consider information on our website to be part of this report unless specifically incorporated herein by reference. You may obtain copies of any or all of the documents

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incorporated by reference in this prospectus supplement or the accompanying prospectus from us free of charge by requesting them in writing or by telephone at the following address:

Chief Financial Officer

A10 Networks, Inc.

2300 Orchard Parkway, San Jose, California 95131

Telephone: (408) 325-8668

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PROSPECTUS

LOGO

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

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.

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.

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.

A10 NETWORKS, INC.

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.

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.

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.

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;

•

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;

•

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.

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:

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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

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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.

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:

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evidence the assumption by a successor entity of our obligations;

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

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add any additional events of default;

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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;

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add guarantees with respect to or secure any debt securities;

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

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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;

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

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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

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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:

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extend the final maturity of any debt security;

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reduce the principal amount or premium, if any;

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

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

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

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

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

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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.

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:

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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

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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.

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.

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.

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.

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:

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the depositary has redeemed all related outstanding depositary shares, or

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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

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.

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:

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the title of the warrants;

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the aggregate number of the warrants;

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

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

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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;

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

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

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

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

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

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a discussion of certain federal income tax considerations; and

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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.

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:

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

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

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

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.

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.

PLAN OF DISTRIBUTION

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

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through underwriters or dealers;

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through agents;

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directly to one or more purchasers;

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in short or long transactions; or

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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:

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

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

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

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any public offering price;

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

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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.

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:

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

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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;

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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;

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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,

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.

LOGO

A10 NETWORKS, INC.

153,962 Shares of Common Stock

PROSPECTUS SUPPLEMENT

August 6, 2026