ALTR Altair Engineering Inc

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-231948

The information in this preliminary prospectus supplement is not complete and may be changed. A registration statement relating to the securities has become effective under the Securities Act of 1933, as amended. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell the securities and are not soliciting an offer to buy the securities in any jurisdiction where the offer or sale is not permitted.

Subject to completion, dated June 4, 2019

Prospectus supplement

(To prospectus dated June 4, 2019)

$175,000,000

    % Convertible Senior Notes due 2024

Interest payable June 1 and December 1

We are offering $175,000,000 principal amount of our     % Convertible Senior Notes due 2024 (the “notes”). The notes will bear interest at a rate of     % per year, payable semiannually in arrears on June 1 and December 1 of each year, beginning on December 1, 2019. The notes will mature on June 1, 2024, unless earlier repurchased, redeemed or converted. This prospectus supplement and the accompanying prospectus also register the offering and sale of the shares of common stock issuable upon conversion of the notes.

Holders may convert their notes at their option at any time prior to the close of business on the business day immediately preceding December 1, 2023 only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on September 30, 2019 (and only during such calendar quarter), if the last reported sale price of our Class A common stock, par value $0.0001 per share (“Class A common stock”), for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five business day period after any five consecutive trading day period (the “measurement period”) in which the trading price (as defined in this prospectus supplement) per $1,000 principal amount of notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of our Class A common stock and the conversion rate on each such trading day; (3) if we call any or all of the notes for redemption, at any time prior to the close of business on the scheduled trading day immediately preceding the redemption date; or (4) upon the occurrence of specified corporate events. On or after December 1, 2023 until the close of business on the business day immediately preceding the maturity date, holders may convert their notes at any time, regardless of the foregoing circumstances. Upon conversion, we will pay or deliver, as the case may be, cash, shares of our Class A common stock or a combination of cash and shares of our Class A common stock, at our election, as described in this prospectus supplement.

The conversion rate will initially be                  shares of Class A common stock per $1,000 principal amount of notes (equivalent to an initial conversion price of approximately $             per share of Class A common stock). The conversion rate will be subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date or if we deliver a notice of redemption, we will, in certain circumstances, increase the conversion rate for a holder who elects to convert its notes in connection with such a corporate event or redemption, as the case may be.

We may not redeem the notes prior to June 6, 2022. We may redeem for cash all or any portion of the notes, at our option, on or after June 6, 2022 if the last reported sale price of our Class A common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive), during any 30 consecutive trading day period (including the last trading day of such period) ending on, and including, the trading day immediately preceding the date on which we provide notice of redemption at a redemption price equal to 100% of the principal amount of the notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. No sinking fund is provided for the notes.

If we undergo a fundamental change, as defined in this prospectus supplement, holders may require us to repurchase for cash all or any portion of their notes at a fundamental change repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

The notes will be our senior unsecured obligations and will rank senior in right of payment to any of our indebtedness that is expressly subordinated in right of payment to the notes; equal in right of payment to any of our unsecured indebtedness that is not so subordinated; effectively junior in right of payment to any of our secured indebtedness to the extent of the value of the assets securing such indebtedness; and structurally junior to all indebtedness and other liabilities (including trade payables) of our subsidiaries.

We do not intend to apply to list the notes on any securities exchange or any automated dealer quotation system. Our Class A common stock is listed on the Nasdaq Global Select Market under the symbol “ALTR.” The last reported sale price of our Class A common stock on the Nasdaq Global Select Market on June 3, 2019 was $36.82 per share.

Investing in the notes involves a high degree of risk. See “ Risk factors ” beginning on page S-10 of this prospectus supplement and the documents incorporated by reference herein for a discussion of certain risks that you should consider in connection with an investment in the notes.

We have granted the underwriters the right to purchase, exercisable within a 30-day period, up to an additional $26,250,000 principal amount of notes.

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

We expect that delivery of the notes will be made to investors in book-entry form through The Depository Trust Company on or about June     , 2019.

June     , 2019

Table of contents

Prospectus supplement

All references in this prospectus supplement and the accompanying prospectus to “Altair,” “the Company,” “we,” “us,” “our” and similar terms refer to Altair Engineering Inc. and its subsidiaries, unless we state otherwise or the context otherwise requires.

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About this prospectus supplement

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. The second part, the accompanying prospectus, gives more general information, some of which may not apply to this offering. You should read this prospectus supplement and the accompanying prospectus, including the information incorporated by reference herein and therein and any free writing prospectus we have authorized for use in connection with this offering, in their entirety before making an investment decision.

If anyone provides you with different or inconsistent information, you should not rely on it. You should assume that the information in this prospectus supplement, the accompanying prospectus, any document incorporated by reference herein or therein and any free writing prospectus we have authorized for use in connection with this offering are accurate or complete only as of their respective dates, regardless of the time of delivery of this prospectus supplement, the accompanying prospectus and any authorized free writing prospectus. Our business, financial condition, results of operations and prospects may have changed since those dates.

In this prospectus supplement, as permitted by law, we “incorporate by reference” information from other documents that we file with the Securities and Exchange Commission (the “SEC”). This means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be a part of this prospectus supplement and the accompanying prospectus and should be read with the same care. When we update the information contained in this prospectus supplement in documents that have been incorporated by reference herein by making future filings with the SEC, that are incorporated by reference herein, the information included or incorporated by reference in this prospectus supplement is considered to be automatically updated and superseded. In other words, in case of a conflict or inconsistency between information contained in this prospectus supplement and information in the accompanying prospectus or incorporated by reference into this prospectus supplement, you should rely on the information contained in the document that was filed with the SEC later. See “Incorporation of certain documents by reference” in this prospectus supplement.

We are not, and the underwriters are not, making an offer to sell the securities in any jurisdiction where the offer or sale is not permitted or in which the person making such offer or solicitation is not qualified to do so or to any person to whom it is unlawful to make such offer or solicitation.

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

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Cautionary note regarding forward-looking statements

This prospectus supplement and the accompanying prospectus, including the documents incorporated by reference into this prospectus supplement and the accompanying prospectus, and any free writing prospectus we authorize for use in connection with this offering may contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), which are subject to risks and uncertainties. These forward-looking statements include statements with respect to our beliefs, plans, objectives, goals, expectations, anticipations, assumptions, estimates, intentions and future performance, and involve known and unknown risks, uncertainties and other factors, which may be beyond our control, and which may cause our actual results, performance or achievements to be materially different from future results, performance or achievements expressed or implied by such forward-looking statements. All statements other than statements of historical fact are statements that could be forward-looking statements. You can identify these forward-looking statements through our use of words such as “may,” “can,” “anticipate,” “assume,” “should,” “indicate,” “would,” “believe,” “contemplate,” “expect,” “seek,” “estimate,” “continue,” “plan,” “point to,” “project,” “predict,” “could,” “intend,” “target,” “potential”, the negative and plural of these words and other similar words and expressions of the future. There are a number of important factors that could cause the actual results to differ materially from those expressed in any forward-looking statement made by us. These factors include, but are not limited to:

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Forward-looking statements are not guarantees of future performance and involve risks and uncertainties. Such forward-looking statements included or incorporated by reference in this prospectus supplement, the accompanying prospectus or any applicable free writing prospectus are based on information available to us as of the date such statements were made and our then-current expectations about future events, which are inherently subject to change and involve risks and uncertainties. All forward-looking statements are expressly qualified in their entirety by this cautionary notice. You should not place undue reliance on these forward-looking statements. Actual events or results may differ materially from those expressed or implied by these statements due to various factors, including but not limited to the factors discussed under the heading “Item 1A. Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2018 (the “2018 Form 10-K”) and under the heading “Risk factors” in this prospectus supplement and the accompanying prospectus.

We do not undertake any obligation to update any forward-looking statements included or incorporated by reference in this prospectus supplement or the accompanying prospectus or any applicable free writing prospectus, whether as a result of new information, future events, or otherwise, except as required by law. All such forward-looking statements should be read as of the time the statements were made and with the recognition that these forward-looking statements may not be complete or accurate at a later date. We have expressed our expectations, beliefs and projections in good faith and we believe they have a reasonable basis. However, we cannot assure you that our expectations, beliefs or projections will result or be achieved or accomplished.

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Risk factors

Investing in our notes involves a high degree of risk. In addition to the other information contained in this prospectus supplement, the accompanying prospectus and in the documents that we incorporate by reference herein and therein, you should carefully consider the risks discussed below and under the heading “Item IA. Risk Factors” in our 2018 Form 10-K before making a decision about investing in the notes. The risks and uncertainties discussed below and in our 2018 Form 10-K are not the only ones facing us. Additional risks and uncertainties not presently known to us, or that we currently see as immaterial, may also harm our business. If any of these risks occur, our business, financial condition and operating results could be harmed, the trading price of the notes and our Class A common stock could decline and you could lose part or all of your investment.

Risks related to the notes

The notes are effectively subordinated to our secured debt and any liabilities of our subsidiaries.

The notes will rank senior in right of payment to any of our indebtedness that is expressly subordinated in right of payment to the notes; equal in right of payment to any of our liabilities that are not so subordinated; effectively junior in right of payment to any of our secured indebtedness (including all amounts outstanding under our revolving credit facility) to the extent of the value of the assets securing such indebtedness; and structurally junior to all indebtedness and other liabilities (including trade payables) of our subsidiaries. In the event of our bankruptcy, liquidation, reorganization or other winding up, our assets that secure debt ranking senior or equal in right of payment to the notes (including all amounts outstanding under our revolving credit facility) will be available to pay obligations on the notes only after the secured debt has been repaid in full from these assets, and the assets of our subsidiaries will be available to pay obligations on the notes only after all claims senior to the notes have been repaid in full. There may not be sufficient assets remaining to pay amounts due on any or all of the notes then outstanding. The indenture governing the notes will not prohibit us from incurring additional senior debt or secured debt, nor does it prohibit any of our subsidiaries from incurring additional liabilities.

As of March 31, 2019, we and our subsidiaries had total consolidated indebtedness of $16.2 million, of which an aggregate of $14.8 million was secured indebtedness of ours. As of March 31, 2019, our subsidiaries had $98.0 million of indebtedness and other liabilities (including trade payables, but excluding intercompany obligations and liabilities of a type not required to be reflected on a balance sheet of such subsidiaries in accordance with GAAP) to which the notes would have been structurally subordinated. After giving effect to the issuance of the notes (assuming no exercise of the underwriters’ option to purchase additional notes) and the use of proceeds therefrom, our total consolidated indebtedness as of March 31, 2019 would have been $176.4 million.

The notes are our obligations only and a substantial portion of our operations are conducted through, and a substantial portion of our consolidated assets are held by, our subsidiaries.

The notes are our obligations exclusively and are not guaranteed by any of our operating subsidiaries. A substantial portion of our operations is conducted through, and a substantial portion of our consolidated assets is held by, our subsidiaries. Accordingly, our ability to service our debt, including the notes, depends in part on the results of operations of our subsidiaries and upon the ability of such subsidiaries to provide us with cash, whether in the form of dividends, loans or otherwise, to pay amounts due on our obligations, including the notes. Our subsidiaries are separate and distinct legal entities and have no obligation, contingent or otherwise, to make payments on the notes or to make any funds available for that purpose. In addition, dividends, loans or other distributions to us from such subsidiaries may be subject to contractual and other restrictions and are subject to other business considerations.

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After this offering, servicing our debt will require a significant amount of cash, and we may not have sufficient cash flow from our business to pay our substantial debt.

Our ability to make scheduled payments of the principal of, to pay interest on or to refinance our future indebtedness, including the amounts payable under our revolving credit facility and the notes, depends on our future performance, which is subject to economic, financial, competitive and other factors beyond our control. Our business may not continue to generate cash flow from operations in the future sufficient to service our debt and make necessary capital expenditures. If we are unable to generate such cash flow, we may be required to adopt one or more alternatives, such as selling assets, restructuring debt or obtaining additional equity capital on terms that may be onerous or highly dilutive. Our ability to refinance our indebtedness will depend on the capital markets and our financial condition at such time. We may not be able to engage in any of these activities or engage in these activities on desirable terms, which could result in a default on our debt obligations. In addition, any of our future debt agreements may contain restrictive covenants that may prohibit us from adopting any of these alternatives. Our failure to comply with these covenants could result in an event of default which, if not cured or waived, could result in the acceleration of our debt.

Recent and future regulatory actions and other events may adversely affect the trading price and liquidity of the notes.

We expect that many investors in, and potential purchasers of, the notes will employ, or seek to employ, a convertible arbitrage strategy with respect to the notes. Investors would typically implement such a strategy by selling short the Class A common stock underlying the notes and dynamically adjusting their short position while continuing to hold the notes. Investors may also implement this type of strategy by entering into swaps on our Class A common stock in lieu of or in addition to short selling the Class A common stock.

The SEC and other regulatory and self-regulatory authorities have implemented various rules and taken certain actions, and may in the future adopt additional rules and take other actions, that may impact those engaging in short selling activity involving equity securities (including our Class A common stock) and securities convertible or exchangeable for equity securities (including the notes). Such rules and actions include Rule 201 of SEC Regulation SHO, the adoption by the Financial Industry Regulatory Authority, Inc. and the national securities exchanges of a “Limit Up-Limit Down” program, the imposition of market-wide circuit breakers that halt trading of securities for certain periods following specific market declines, and the implementation of certain regulatory reforms required by the Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010. Any governmental or regulatory action that restricts the ability of investors in, or potential purchasers of, the notes to effect short sales of our Class A common stock, borrow our Class A common stock or enter into swaps on our Class A common stock could adversely affect the trading price and the liquidity of the notes.

Hedging or arbitrage trading or volatility in the market price and trading volume of our Class A common stock could adversely impact the trading price of the notes.

We expect that the trading price of the notes will be significantly affected by the market price of our Class A common stock. The stock market in recent years has experienced significant price and volume fluctuations that have often been unrelated to the operating performance of companies. The market price of our Class A common stock could fluctuate significantly for many reasons, including in response to the risks described in this section, elsewhere in this prospectus supplement or the documents we have incorporated by reference in this prospectus supplement or for reasons unrelated to our operations, such as reports by industry analysts, investor perceptions or negative announcements by our customers, competitors or suppliers regarding their own performance, as well as industry conditions and general financial, economic and political instability. A decrease in the market price of our Class A common stock would likely adversely impact the trading price of the notes. The market price of our Class A common stock could also be affected by possible sales of our Class A

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common stock by investors who view the notes as a more attractive means of equity participation in us and by hedging or arbitrage trading activity that we expect to develop involving our Class A common stock. This hedging or arbitrage trading activity could, in turn, affect the trading price of the notes.

We may still incur substantially more debt or take other actions which would intensify the risks discussed above.

We and our subsidiaries may be able to incur substantial additional debt in the future, subject to the restrictions contained in our debt instruments, some of which may be secured debt. We will not be restricted under the terms of the indenture governing the notes from incurring additional debt, securing existing or future debt, recapitalizing our debt or taking a number of other actions that are not limited by the terms of the indenture governing the notes that could have the effect of diminishing our ability to make payments on the notes when due. Our existing revolving credit facility restricts our ability to incur additional indebtedness, including secured indebtedness, but if the facility matures or is repaid, we may not be subject to such restrictions under the terms of any subsequent indebtedness.

We may not have the ability to raise the funds necessary to settle conversions of the notes in cash or to repurchase the notes upon a fundamental change, and our current debt contains, and our future debt may contain, limitations on our ability to pay cash upon conversion or repurchase of the notes.

Holders of the notes will have the right to require us to repurchase their notes upon the occurrence of a fundamental change at a fundamental change repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus accrued and unpaid interest, if any, as described under “Description of notes—Fundamental change permits holders to require us to repurchase notes.” In addition, upon conversion of the notes, unless we elect to deliver solely shares of our Class A common stock to settle such conversion (other than paying cash in lieu of delivering any fractional share), we will be required to make cash payments in respect of the notes being converted as described under “Description of notes—Conversion rights—Settlement upon conversion.” However, we may not have enough available cash or be able to obtain financing at the time we are required to make repurchases of notes surrendered therefor or notes being converted.

In addition, our ability to repurchase the notes or to pay cash upon conversions of the notes may be limited by law, by regulatory authority or by agreements governing our indebtedness including our existing revolving credit facility. Our failure to repurchase notes at a time when the repurchase is required by the indenture or to pay any cash payable on future conversions of the notes as required by the indenture would constitute a default under the indenture. A default under the indenture or the occurrence of a fundamental change itself would likely also lead to a default under our revolving credit facility, and may lead to a default under agreements governing our future indebtedness. If the repayment of the related indebtedness were to be accelerated after any applicable notice or grace periods, we may not have sufficient funds to repay the indebtedness and repurchase the notes or make cash payments upon conversions thereof.

Redemption may adversely affect your return on the notes.

We may not redeem the notes prior to June 6, 2022. We may redeem for cash all or any portion of the notes, at our option, on or after June 6, 2022 if the last reported sale price of our Class A common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period (including the last trading day of such period) ending on, and including, the trading day immediately preceding the date on which we provide notice of redemption at a redemption price equal to 100% of the principal amount of the notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. As a result, we may choose to redeem some or all of the notes, including at times when prevailing interest rates are relatively low. As a result, you may not be able to reinvest the proceeds

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you receive from the redemption in a comparable security at an effective interest rate as high as the interest rate on your notes being redeemed. See “Description of notes—Optional redemption.”

Our revolving credit facility limits our ability to pay any cash amount upon the conversion or repurchase of the notes.

Our existing revolving credit facility prohibits us from making any cash payments on the conversion or repurchase of the notes if a default under such credit facility exists or would be created thereby. In addition, our ability to make cash payments on the conversion or repurchase of the notes will be limited to the extent we do not satisfy certain financial covenant tests after giving effect to such payments. Any new credit facility that we may enter into may have similar restrictions. Our failure to make cash payments upon the conversion or repurchase of the notes as required under the terms of the notes would permit holders of the notes to accelerate our obligations under the notes.

The conditional conversion feature of the notes, if triggered, may adversely affect our financial condition and operating results.

In the event the conditional conversion feature of the notes is triggered, holders of notes will be entitled to convert the notes at any time during specified periods at their option. See “Description of notes—Conversion rights.” If one or more holders elect to convert their notes, unless we elect to satisfy our conversion obligation by delivering solely shares of our Class A common stock (other than paying cash in lieu of delivering any fractional share), we would be required to settle a portion or all of our conversion obligation through the payment of cash, which could adversely affect our liquidity. In addition, even if holders of notes do not elect to convert their notes, we could be required under applicable accounting rules to reclassify all or a portion of the outstanding principal of the notes as a current rather than long-term liability, which would result in a material reduction of our net working capital.

The accounting method for convertible debt securities that may be settled in cash, such as the notes, could have a material effect on our reported financial results.

Under Financial Accounting Standards Board Accounting Standards Codification 470-20, Debt with Conversion and Other Options (“ASC 470-20”), an entity must separately account for the liability and equity components of the convertible debt instruments (such as the notes) that may be settled entirely or partially in cash upon conversion in a manner that reflects the issuer’s economic interest cost. The effect of ASC 470-20 on the accounting for the notes is that the equity component is required to be included in the additional paid-in capital section of stockholders’ equity on our consolidated balance sheet, and the value of the equity component would be treated as debt discount for purposes of accounting for the debt component of the notes. As a result, we will be required to record a greater amount of non-cash interest expense in current periods presented as a result of the amortization of the discounted carrying value of the notes to their face amount over the term of the notes. We will report larger net losses (or lower net income) in our financial results because ASC 470-20 will require interest to include both the current period’s amortization of the debt discount and the instrument’s coupon interest, which could adversely affect our reported or future financial results, the trading price of our Class A common stock and the trading price of the notes.

In addition, under certain circumstances, convertible debt instruments (such as the notes) that may be settled entirely or partly in cash are currently accounted for utilizing the treasury stock method, the effect of which is that the shares issuable upon conversion of the notes are not included in the calculation of diluted earnings per share except to the extent that the conversion value of the notes exceeds their principal amount. Under the treasury stock method, for diluted earnings per share purposes, the transaction is accounted for as if the number of shares of Class A common stock that would be necessary to settle such excess, if we elected to settle such excess in shares, are issued. We cannot be sure that the accounting standards in the future will continue to

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permit the use of the treasury stock method. If we are unable to use the treasury stock method in accounting for the shares issuable upon conversion of the notes, then our diluted earnings per share would be adversely affected.

Future sales of our Class A common stock or equity-linked securities in the public market, could lower the market price for our Class A common stock and adversely impact the trading price of the notes.

In the future, we may sell shares of our Class A common stock or equity-linked securities to raise capital. In addition, a substantial number of shares of our Class A common stock are reserved for issuance upon the exercise of our outstanding stock options, settlement of other equity incentive awards, and conversion of the notes. We cannot predict the size of future issuances or the effect, if any, that they may have on the market price for our Class A common stock. The issuance and sale of substantial amounts of Class A common stock or equity-linked securities, or the perception that such issuances and sales may occur, could adversely affect the trading price of the notes and the market price of our Class A common stock and impair our ability to raise capital through the sale of additional equity or equity-linked securities.

Holders of notes will not be entitled to any rights with respect to our Class A common stock, but they will be subject to all changes made with respect to them to the extent our conversion obligation includes shares of our Class A common stock.

Holders of notes will not be entitled to any rights with respect to our Class A common stock (including, without limitation, voting rights and rights to receive any dividends or other distributions on our Class A common stock) prior to the conversion date relating to such notes (if we have elected to settle the relevant conversion by delivering solely shares of our Class A common stock (other than paying cash in lieu of delivering any fractional share)) or the last trading day of the relevant observation period (if we elect to pay and deliver, as the case may be, a combination of cash and shares of our Class A common stock in respect of the relevant conversion), but holders of notes will be subject to all changes affecting our Class A common stock. For example, if an amendment is proposed to our certificate of incorporation or bylaws requiring stockholder approval and the record date for determining the stockholders of record entitled to vote on the amendment occurs prior to the conversion date related to a holder’s conversion of its notes (if we have elected to settle the relevant conversion by delivering solely shares of our Class A common stock (other than paying cash in lieu of delivering any fractional share)) or the last trading day of the relevant observation period (if we elect to pay and deliver, as the case may be, a combination of cash and shares of our Class A common stock in respect of the relevant conversion), such holder will not be entitled to vote on the amendment, although such holder will nevertheless be subject to any changes affecting our Class A common stock.

The conditional conversion feature of the notes could result in your receiving less than the value of our Class A common stock into which the notes would otherwise be convertible.

Prior to the close of business on the business day immediately preceding December 1, 2023, you may convert your notes only if specified conditions are met. If the specific conditions for conversion are not met, you will not be able to convert your notes, and you may not be able to receive the value of the cash, Class A common stock or a combination of cash and Class A common stock, as applicable, into which the notes would otherwise be convertible.

Upon conversion of the notes, you may receive less valuable consideration than expected because the value of our Class A common stock may decline after you exercise your conversion right but before we settle our conversion obligation.

Under the notes, a converting holder will be exposed to fluctuations in the value of our Class A common stock during the period from the date such holder surrenders notes for conversion until the date we settle our conversion obligation.

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Upon conversion of the notes, we have the option to pay or deliver, as the case may be, cash, shares of our Class A common stock, or a combination of cash and shares of our Class A common stock. If we elect to satisfy our conversion obligation in cash or a combination of cash and shares of our Class A common stock, the amount of consideration that you will receive upon conversion of your notes will be determined by reference to the volume-weighted average price of our Class A common stock for each trading day in a 50 trading day observation period. As described under “Description of notes—Conversion rights—Settlement upon conversion,” this period would be (i) subject to clause (ii), if the relevant conversion date occurs prior to December 1, 2023, the 50 consecutive trading day period beginning on, and including, the second trading day immediately succeeding such conversion date; (ii) if the relevant conversion date occurs during a redemption period with respect to the notes as described under “Description of notes—Optional redemption,” the 50 consecutive trading days beginning on, and including, the 51st trading day immediately preceding such redemption date; and (iii) if the relevant conversion date occurs on or after December 1, 2023, the 50 consecutive trading days beginning on, and including, the 51st trading day immediately preceding the maturity date. Accordingly, if the price of our Class A common stock decreases during this period, the amount and/or value of consideration you receive will be adversely affected. In addition, if the market price of our Class A common stock at the end of such period is below the average of the daily volume-weighted average prices of our Class A common stock during such period, the value of any shares of our Class A common stock that you will receive in satisfaction of our conversion obligation will be less than the value used to determine the number of shares that you will receive.

If we elect to satisfy our conversion obligation solely in shares of our Class A common stock upon conversion of the notes, we will be required to deliver the shares of our Class A common stock, together with cash for any fractional share, on the second business day following the relevant conversion date. Accordingly, if the price of our Class A common stock decreases during this period, the value of the shares that you receive will be adversely affected and would be less than the conversion value of the notes on the conversion date.

The notes are not protected by restrictive covenants.

The indenture governing the notes will not contain any financial or operating covenants or restrictions on the payments of dividends (other than in connection with adjustments to the conversion rate), the incurrence of indebtedness or the issuance or repurchase of securities by us or any of our subsidiaries. The indenture will not contain any covenants or other provisions to afford protection to holders of the notes in the event of a fundamental change or other corporate transaction involving us except to the extent described under “Description of notes—Fundamental change permits holders to require us to repurchase notes,” “Description of notes—Conversion rights—Increase in conversion rate upon conversion upon a make-whole fundamental change or during a redemption period” and “Description of notes—Consolidation, merger and sale of assets.”

The increase in the conversion rate for notes converted in connection with a make-whole fundamental change or during a redemption period may not adequately compensate you for any lost value of your notes as a result of such transaction or redemption.

If a make-whole fundamental change occurs prior to the maturity date or upon our issuance of a notice of redemption, under certain circumstances, we will increase the conversion rate by a number of additional shares of our Class A common stock for notes converted in connection with such make-whole fundamental change or during the related redemption period. The increase in the conversion rate will be determined based on the date on which the specified corporate transaction becomes effective or the date of the redemption notice, as applicable, and the price paid (or deemed to be paid) per share of our Class A common stock in such transaction or on such redemption notice date, as described below under “Description of notes—Conversion rights—Increase in conversion rate upon conversion upon a make-whole fundamental change or during a redemption period.” The increase in the conversion rate for notes converted in connection with a make-whole fundamental change

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or during a redemption period, as applicable, may not adequately compensate you for any lost value of your notes as a result of such transaction or in connection with the relevant redemption, as applicable. In addition, if the price per share of our Class A common stock paid (or deemed paid) in the transaction or in connection with the relevant redemption, as applicable, is greater than $         per share or less than $         per share (in each case, subject to adjustment), no additional shares will be added to the conversion rate. Moreover, in no event will the conversion rate per $1,000 principal amount of notes as a result of this adjustment exceed              shares of Class A common stock, subject to adjustment in the same manner as the conversion rate as set forth under “Description of notes—Conversion rights—Conversion rate adjustments.”

Our obligation to increase the conversion rate for notes converted in connection with a make-whole fundamental change or during a redemption period could be considered a penalty, in which case the enforceability thereof would be subject to general principles of reasonableness and equitable remedies.

Upon any redemption of the notes on or after June 6, 2022, the cash comprising the redemption price may not fully compensate you for future interest payments or the lost time value of your notes.

On or after June 6, 2022, we may redeem for cash all or any portion of the notes, at our option, if the last reported sale price of our Class A common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period (including the last trading day of such period) ending on, and including, the trading day immediately preceding the date on which we provide notice of redemption at a redemption price equal to 100% of the principal amount of the notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. Upon such redemption, the cash comprising the redemption price may not fully compensate you for any future interest payments that you would have otherwise received or any other lost time value of your notes. See “Description of notes—Optional redemption.”

The conversion rate of the notes may not be adjusted for all dilutive events.

The conversion rate of the notes is subject to adjustment for certain events, including, but not limited to, the issuance of certain stock dividends on our Class A common stock, the issuance of certain rights or warrants, subdivisions, combinations, distributions of capital stock, indebtedness, or assets, cash dividends and certain issuer tender or exchange offers as described under “Description of notes—Conversion rights—Conversion rate adjustments.” However, the conversion rate will not be adjusted for other events, such as a third-party tender or exchange offer or an issuance of Class A common stock for cash, that may adversely affect the trading price of the notes or our Class A common stock. An event that adversely affects the value of the notes may occur, and that event may not result in an adjustment to the conversion rate.

Some significant restructuring transactions may not constitute a fundamental change, in which case we would not be obligated to offer to repurchase the notes.

Upon the occurrence of a fundamental change, you have the right to require us to repurchase your notes. However, the fundamental change provisions will not afford protection to holders of notes in the event of other transactions that could adversely affect the notes. For example, transactions such as leveraged recapitalizations, refinancings, restructurings, or acquisitions initiated by us may not constitute a fundamental change requiring us to offer to repurchase the notes. In the event of any such transaction, the holders would not have the right to require us to repurchase the notes, even though each of these transactions could increase the amount of our indebtedness, or otherwise adversely affect our capital structure or any credit ratings, thereby adversely affecting the holders of notes.

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We cannot assure you that an active trading market will develop for the notes.

Prior to this offering, there has been no trading market for the notes, and we do not intend to apply to list the notes on any securities exchange or to arrange for quotation on any automated dealer quotation system. We have been informed by the underwriters that they intend to make a market in the notes after the offering is completed. However, the underwriters may cease their market-making at any time without notice. In addition, the liquidity of the trading market in the notes, and the market price quoted for the notes, may be adversely affected by changes in the overall market for this type of security and by changes in our financial performance or prospects or in the prospects for companies in our industry generally. As a result, we cannot assure you that an active trading market will develop for the notes. We believe that historically the market for non-investment grade debt has been subject to severe disruptions that have caused substantial volatility in the prices of securities similar to the notes. The market, if any, for the notes may experience similar disruptions and any such disruptions may materially adversely affect the liquidity in that market or the prices at which you may sell your notes. In addition, subsequent to the initial issuance of the notes, the notes may trade at a discount from their initial offering price, depending upon prevailing interest rates, the market for similar notes, our performance and other factors. If an active trading market does not develop or is not maintained, the market price and liquidity of the notes may be adversely affected. In that case you may not be able to sell your notes at a particular time or you may not be able to sell your notes at a favorable price.

Any adverse rating of the notes may cause their trading price to fall.

We do not intend to seek a rating on the notes. However, if a rating service were to rate the notes and if such rating service were to lower its rating on the notes below the rating initially assigned to the notes or otherwise announces its intention to put the notes on credit watch, the trading price of the notes could decline.

You may be subject to tax if we make or fail to make certain adjustments to the conversion rate of the notes even though you do not receive a corresponding cash distribution.

The conversion rate of the notes is subject to adjustment in certain circumstances, including the payment of cash dividends. If the conversion rate is adjusted as a result of a distribution that is taxable to our Class A common stockholders, such as a cash dividend, you may be deemed to have received a dividend subject to U.S. federal income tax without the receipt of any cash. In addition, a failure to adjust (or to adjust adequately) the conversion rate after an event that increases your proportionate interest in us could be treated as a deemed taxable dividend to you. If a make-whole fundamental change occurs prior to the maturity date or we issue a notice of redemption, under some circumstances, we will increase the conversion rate for notes converted in connection with the make-whole fundamental change or during the related redemption period. Such increase may also be treated as a distribution subject to U.S. federal income tax as a dividend. See “Material U.S. federal income tax considerations.” If you are a non-U.S. holder (as defined in “Material U.S. federal income tax considerations”), any deemed dividend would generally be subject to U.S. federal withholding tax at a 30% rate, or such lower rate as may be specified by an applicable treaty, which may be set off against subsequent payment on the notes. See “Material U.S. federal income tax considerations.”

Our management has broad discretion in the use of the net proceeds from this offering, and our use of the net proceeds may not enhance our operating results or the price of the notes and our Class A common stock.

We intend to use the net proceed from this offering to repay outstanding indebtedness under our revolving credit facility, for acquisitions of, or investments in, technologies, solutions or businesses that complement our business and for other general corporate purposes, including working capital, developing and building an addition adjacent to our corporate headquarters facilities and related real estate development matters, sales and marketing activities, general and administrative matters and capital expenditures. While we do not have agreements or binding commitments for any specific acquisitions at this time, we continually evaluate potential

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acquisition candidates to enhance our product offerings. Accordingly, our management will have considerable discretion over the specific use of the net proceeds that we receive in this offering and might not be able to obtain a significant return, if any, on investment of these net proceeds. You will not have the opportunity as part of your investment decision to assess whether the net proceeds are being used appropriately. Investors in this offering will need to rely upon the judgment of our management with respect to the use of proceeds. Until the net proceeds are used, they may be placed in investments that do not produce significant income, may be held in demand deposit accounts, or in investments intended to be highly liquid that may nevertheless lose value. If we do not use the net proceeds that we receive in this offering effectively, our business and prospects could be harmed, and the market price of the notes and our Class A common stock could decline.

Because the notes will initially be held in book-entry form, holders must rely on DTC’s procedures to receive communications relating to the notes and exercise their rights and remedies.

We will initially issue the notes in the form of one or more global notes registered in the name of Cede & Co., as nominee of DTC. Beneficial interests in global notes will be shown on, and transfers of global notes will be effected only through, the records maintained by DTC. Except in limited circumstances, we will not issue certificated notes. See “Description of notes—Book-entry, settlement and clearance.” Accordingly, if you own a beneficial interest in a global note, then you will not be considered an owner or holder of the notes. Instead, DTC or its nominee will be the sole holder of the notes. Unlike persons who have certificated notes registered in their names, owners of beneficial interests in global notes will not have the direct right to act on our solicitations for consents or requests for waivers or other actions from holders. Instead, those beneficial owners will be permitted to act only to the extent that they have received appropriate proxies to do so from DTC or, if applicable, a DTC participant. The applicable procedures for the granting of these proxies may not be sufficient to enable owners of beneficial interests in global notes to vote on any requested actions on a timely basis. In addition, notices and other communications relating to the notes (including any notice of redemption) will be sent to DTC. We expect DTC to forward any such communications to DTC participants, which in turn would forward such communications to indirect DTC participants. But we can make no assurances that you will timely receive any such communications.

Risks related to our Class A common stock

An active public trading market for our Class A common stock may not be sustained.

Prior to our initial public offering in the fourth quarter of 2017, there had been no public market or active private market for trading shares of our Class A common stock. Our Class A common stock is listed on the Nasdaq Global Select Market under the symbol “ALTR.” However, we cannot assure you that an active trading market will be sustained. The lack of an active market may impair your ability to sell your shares at the time you wish to sell them or at a price that you consider reasonable. The lack of an active market may also reduce the price of shares of Class A common stock. We may need additional financing to execute on our current or future business strategies, including to develop new or enhance existing products and services, acquire businesses and technologies, or otherwise to respond to competitive pressure. An inactive market may impair our ability to raise capital by selling shares and our ability to use our capital stock to acquire other companies or technologies. We cannot predict the prices at which our Class A common stock will trade.

The market price of our Class A common stock can be volatile.

The market price of our Class A common stock has fluctuated substantially since our IPO. Our market price may continue to fluctuate substantially depending on a number of factors, many 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 Class A common stock, since you might not be able to sell your shares at or above the

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price you paid for our Class A common stock. Factors that could cause fluctuations in the market price of our Class A common stock include the following:

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In addition, the stock market in general, and the market for technology companies in particular, have experienced extreme price and volume fluctuations that have often been unrelated or disproportionate to the operating performance of those companies. Broad market and industry factors may affect the market price of our Class A common stock, regardless of our actual operating performance. In the past, following periods of volatility in the overall market and the market prices of a particular company’s securities, securities class action litigation has often been instituted against that company. We may become the target of this type of litigation in the future. Securities litigation, if instituted against us, could result in substantial costs and divert our management’s attention and resources from our business.

Any future sales of substantial amounts of our Class A common stock or equity-linked securities in the public markets, or the perception that such sales might occur, could reduce the price that our Class A common stock might otherwise attain and may dilute the voting power and ownership interest in us of our then-existing stockholders.

We have registered the offer and sale of an aggregate of 19,960,830 shares of Class A common stock that have been issued or reserved for future issuance under our equity compensation plans on a Form S-8 registration statement. These shares can be freely sold in the public market upon issuance, unless they are held by “affiliates,” as that term is defined in Rule 144 of the Securities Act. Additionally, the number of shares of Class A common stock available for grant and issuance under our 2017 Equity Incentive Plan is subject to an automatic annual increase on January 1 of each year by an amount equal to the lesser of (i) 3% of the number of shares of all classes of our common stock outstanding on December 31 of the preceding calendar year or (ii) a lesser number of shares of Class A common stock determined by our board of directors. We also intend to register the offer and sale of any shares of Class A common stock resulting from such increases. If the holders of these shares choose to sell a large number of shares, they could adversely affect the market price for our Class A common stock.

In addition, in the future, we may sell additional shares of our Class A common stock or equity-linked securities to raise capital. Furthermore, a substantial number of shares of our Class A common stock are reserved for issuance upon conversion of the notes, exercise of our outstanding stock options, or the settlement of other equity incentive awards. We cannot predict the size of future issuances or the effect, if any that they may have on the market price for our Class A common stock. The issuance and sale of substantial amounts of Class A common stock or equity-linked securities, or the perception that such issuances and sales may occur, could adversely affect the trading price of our Class A common stock and the market price of our Class A common stock and impair our ability to raise capital through the sale of additional equity or equity-linked securities.

Subject to certain exceptions described under the caption “Underwriting (conflicts of interest),” we, our directors and our executive officers have agreed not to offer, sell or agree to sell, directly or indirectly, any shares of our common stock or securities convertible into or exercisable or exchangeable for our common stock without the permission of J.P. Morgan Securities LLC, as representative of the underwriters (the “Representative”), for a period of 60 days from the date of this prospectus supplement. When the lock-up period expires, we, such stockholders and our directors and executive officers will be able to sell our shares of common stock in the public market. In addition, the Representative may, in its sole discretion, release all or some portion of the shares of common stock subject to lock-up agreements prior to expiration of the lock-up period. Sales of a substantial number of such shares upon expiration, or the perception that such sales may occur, or early release, of the lock-up could cause our share price to decline or make it more difficult for holders of our Class A common stock to sell such Class A common stock at a time and price that they deem appropriate. Subject to certain limitations, we also may issue our shares of Class A common stock or securities convertible into our Class A common stock from time to time in connection with a financing, an acquisition, investments or otherwise. Any such issuance could result in substantial dilution to our existing stockholders and cause the trading price of our Class A common stock to decline.

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We do not intend to pay dividends in the foreseeable future. As a result, your ability to achieve a return on your investment in our Class A common stock will depend on appreciation in the price of our Class A common stock.

We have never declared or paid any cash dividends on our Class A common stock. We currently intend to retain all available funds and any future earnings for use in the operation of our business and do not anticipate paying any dividends on our Class A common stock in the foreseeable future. Any determination to pay dividends in the future will be at the discretion of our board of directors. Consequently, your only opportunity to achieve a return on your investment in our company will be if the market price of our Class A common stock appreciates and you sell your shares at a profit. There is no guarantee that the price of our Class A common stock will prevail in the market will ever exceed the price that you paid.

Our management team has limited experience managing a public company.

Most members of our management team have limited experience managing a publicly-traded company, interacting with public company investors, and complying with laws pertaining to public companies. Our management team may not successfully or efficiently manage our role as a public company subject to significant regulatory oversight and reporting obligations under the federal securities laws and the continuous scrutiny of securities analysts and investors. These obligations and constituents require significant attention from our senior management and may divert their attention away from the day-to-day management of our business, which could adversely affect our business, financial condition, and operating results.

We are incurring increased costs and devote additional management time as a result of operating as a public company.

As a public company, we are incurring legal, accounting and other expenses that we did not incur as a private company. We are subject to the reporting requirements of the Securities Exchange Act of 1934, as amended, or the Exchange Act, and are required to comply with the applicable requirements of the Sarbanes-Oxley Act of 2002, or SOX, and the Dodd-Frank Wall Street Reform and Consumer Protection Act, or Dodd-Frank, as well as rules and regulations subsequently implemented by the SEC and the Nasdaq Global Select Market, including the establishment and maintenance of effective disclosure and financial controls and changes in corporate governance practices.

As of December 31, 2018, we ceased to be an “emerging growth company”, as defined by the Jumpstart Our Business Startups Act, or JOBS Act, which has the effect of expanding disclosure and other obligations applicable to us, including, but not limited to, enhanced disclosure obligations regarding executive compensation in our periodic reports and proxy statements and the requirements of holding a nonbinding advisory vote on executive compensation and stockholder approval of any golden parachute payments not previously approved, along with accelerated compliance with SOX and earlier implementation of certain changes in GAAP such as revenue recognition and leasing standards. Compliance with these requirements increases our legal and financial compliance costs and makes some activities more time consuming and costly. In addition, our management and other personnel need to divert attention from operational and other business matters to devote time to these public company requirements. In particular, we have incurred, and expect to continue to incur, additional expenses and have devoted, and expect to continue to devote, additional management effort toward ensuring compliance with the requirements of Section 404 of SOX, as a result of our ceasing to be an emerging growth company. Although we have already hired additional employees to help comply with these requirements, we may need to further expand our legal and finance departments in the future, which will increase our costs and expenses.

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If we fail to maintain effective internal controls, we may not be able to report financial results accurately or on a timely basis, or to detect fraud, which could have a material adverse effect on our business or share price.

Effective internal controls are necessary for us to provide reasonable assurance with respect to our financial reports and to effectively prevent financial fraud. Pursuant to SOX, we are required to periodically evaluate the effectiveness of the design and operation of our internal controls. Internal controls over financial reporting may not prevent or detect misstatements because of inherent limitations, including the possibility of human error or collusion, the circumvention or overriding of controls, or fraud. If we fail to maintain an effective system of internal controls, our business and operating results could be harmed, and we could fail to meet our reporting obligations, which could have a material adverse effect on our business and our share price.

As a public company, we are required to maintain internal controls over financial reporting and to report any material weaknesses in such internal controls. Section 404 of SOX requires annual management assessments of the effectiveness of our internal controls over financial reporting beginning with our 2018 Form 10-K. We have designed, implemented and tested the internal control over financial reporting required to comply with this obligation, which was and is time consuming, costly, and complicated. We have identified material weaknesses in our internal controls over financial reporting for the fiscal years ended December 31, 2016 and 2017, one of which has not been remediated as of our fiscal year 2018. If we identify material weaknesses in our internal control over financial reporting in the future or if we are unable to successfully remediate the identified material weaknesses or, if we are unable to comply with the requirements of Section 404 in a timely manner or assert that our internal control over financial reporting is effective, investors may lose confidence in the accuracy and completeness of our financial reports and the market price of our Class A common stock could be negatively affected, and we could become subject to investigations by the stock exchange on which our securities are listed, the SEC, or other regulatory authorities, which could require additional financial and management resources.

We are a “controlled company” within the meaning of the rules of the Nasdaq Global Select Market and, as a result, we qualify for, but do not currently intend to rely on, exemptions from certain corporate governance requirements. In the event that we were to rely on these exemptions in the future, you would not have the same protections as are afforded to stockholders of companies that are subject to such requirements.

Upon completion of this offering, our co-founders, James R. Scapa, also our chairman and chief executive officer, and George Christ, will continue to control a majority of the combined voting power of our company. As a result, we may be deemed to be a “controlled company” within the meaning of the Nasdaq corporate governance standards. Under the Nasdaq rules, a company of which more than 50% of the voting power is held by an individual, group or another company is a “controlled company” and need not comply with certain requirements, including the requirement that a majority of the Board consist of independent directors and the requirements that our compensation and nominating and governance committees be composed entirely of independent directors. Since our initial public offering, we have not taken advantage of, and following this offering we do not intend to take advantage of, these exemptions. However, for so long as we qualify as a “controlled company,” we have the authority to utilize some or all of these exemptions. If we utilize these exemptions, among other things, we may not have a majority of independent directors and our compensation and nominating and governance committees may not consist entirely of independent directors. Thus, in the event that we were to rely on these exemptions in the future, you would not have the same protections as are afforded to stockholders of companies that are subject to all of the corporate governance requirements of Nasdaq.

The dual class structure of our common stock has the effect of concentrating voting control with certain stockholders who hold shares of our Class B common stock, including our founders, certain of our directors and executive officers and affiliates, who will hold in the aggregate 91% of the voting power of our capital stock

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following the completion of this offering. This will limit or preclude your ability to influence corporate matters, including the election of directors, amendments of our organizational documents, and any merger, consolidation, sale of all or substantially all of our assets, or other major corporate transaction requiring stockholder approval.

Our Class B common stock has ten votes per share, and our Class A common stock, which is the common stock that underlies the notes we are offering pursuant to this prospectus, has one vote per share. Following this offering, our Class B stockholders, including our founders, certain of our directors and executive officers, and affiliates, will hold, in the aggregate 91% of the voting power of our capital stock. The ten-to-one voting ratio between our Class B and Class A common stock, results in the holders of our Class B common stock collectively controlling a majority of the combined voting power of our common stock and therefore being able to control all matters submitted to our stockholders for approval until 2029, or upon the occurrence of a triggering event at which time all shares of our Class B common stock will automatically convert into shares of our Class A common stock, or on an earlier date, as set forth in our certificate of incorporation.

This concentrated control will limit or preclude your ability to influence corporate matters for the foreseeable future, including the election of directors, amendments of our organizational documents, and any merger, consolidation, sale of all or substantially all of our assets, or other major corporate transaction requiring stockholder approval. In addition, this may prevent or discourage unsolicited acquisition proposals or offers for our capital stock that you may feel are in your best interest as one of our stockholders.

Future transfers by holders of our Class B common stock will generally result in those shares converting to Class A common stock, subject to the specific exceptions set forth in our certificate of incorporation, such as certain transfers effected for estate planning purposes and between or among our founders. The conversion of Class B common stock to Class A common stock will have the effect, over time, of increasing the relative voting power of those holders of Class B common stock who retain their shares in the long-term. For a description of the dual class structure, see the section entitled “Description of Capital Stock—Class A and Class B Common Stock – Voting rights” in the accompanying prospectus.

We cannot predict the impact our capital structure may have on our stock price.

In July 2017, S&P Dow Jones, a provider of widely followed stock indices, announced that companies with multiple share classes, such as ours, will not be eligible for inclusion in certain of their indices. As a result, our Class A common stock will likely not be eligible for these stock indices. Additionally, FTSE Russell, another provider of widely followed stock indices, has stated that it plans to require new constituents of its indices to have at least five percent of their voting rights in the hands of public stockholders. Many investment funds are precluded from investing in companies that are not included in such indices, and these funds would be unable to purchase our Class A common stock. We cannot assure you that other stock indices will not take a similar approach to S&P Dow Jones or FTSE Russell in the future. Given the sustained flow of investment funds into passive strategies that seek to track certain indexes, exclusion from indices could make our Class A common stock less attractive to investors. As a result, the market price of our Class A common stock could be adversely affected.

If financial or industry analysts do not publish research or reports about our business or if they issue inaccurate or unfavorable commentary or downgrade our Class A common stock, our stock price and trading volume could decline.

The trading market for our Class A common stock may be influenced by the research and reports that industry or financial analysts publish about us or our business. We do not control these analysts, or the content and opinions included in their reports. As a relatively new public company, we may be slow to attract research coverage, and the analysts who publish information about our Class A common stock still have relatively little

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experience with our company, which could affect their ability to accurately forecast our results and make it more likely that we fail to meet their estimates. If any of the analysts who cover us issue an inaccurate or unfavorable opinion regarding our stock price, our stock price would likely decline. In addition, the stock prices of many companies in the technology industry have declined significantly after those companies have failed to meet, or often times failed to exceed, the financial guidance publicly announced by the companies or the expectations of analysts. If our financial results fail to meet, or fail to significantly exceed, our announced guidance or the expectations of analysts or public investors, analysts could downgrade our Class A common stock or publish unfavorable research about us. If one or more of these analysts cease coverage of our company or fail to publish reports on us regularly, we could lose visibility in the financial markets, which in turn could cause our stock price or trading volume to decline.

Certain provisions in our charter documents and Delaware law could prevent an acquisition of our company, limit attempts by our stockholders to replace or remove members of our board of directors or current management and may adversely affect the market price of our Class A common stock.

Our certificate of incorporation and bylaws contain provisions that could delay or prevent a change in control of our company that stockholders may consider favorable, including transactions in which stockholders might otherwise receive a premium for their shares. These provisions may also prevent or delay attempts by stockholders to replace or remove our current management or members of our board of directors. These provisions include:

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In addition, as a Delaware corporation, we are subject to the provisions of Section 203 of the Delaware General Corporation Law. These provisions may prohibit large stockholders, in particular those owning 15% or more of our outstanding voting stock, from merging or combining with us for a certain period of time.

These and other provisions in our certificate of incorporation, our bylaws and under Delaware law could discourage potential takeover attempts, reduce the price that investors might be willing to pay for shares of our Class A common stock in the future and result in the market price being lower than it would be without these provisions.

Our bylaws designate courts in the State of Delaware as the sole and exclusive forums for certain types of actions and proceedings that may be initiated by our stockholders, which could limit our stockholders’ ability to obtain a favorable judicial forum for disputes with us or our directors, officers, or employees.

Our bylaws provide that, subject to limited exceptions, a state or federal court located within the State of Delaware will be the sole and exclusive forums for:

Any person or entity purchasing or otherwise acquiring any interest in shares of our capital stock are deemed to have notice of and to have consented to these provisions. These provisions may limit a stockholder’s ability to bring a claim in a judicial forum that it finds favorable for disputes with us or our directors, officers, or other employees, which may discourage such lawsuits against us and our directors, officers, and employees. Alternatively, if a court were to find these provisions of our bylaws inapplicable to, or unenforceable in respect of, one or more of the specified types of actions or proceedings, we may incur additional costs associated with resolving such matters in other jurisdictions, which could adversely affect our business and financial condition.

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Use of proceeds

We estimate that the net proceeds from the sale of the notes in this offering will be approximately $168.6 million, after deducting estimated underwriting discounts and offering expenses payable by us. If the underwriters’ option to purchase additional notes in this offering is exercised in full, we estimate that the net proceeds from this offering will be approximately $194.0 million, after deducting estimated underwriting discounts and offering expenses payable by us.

We intend to use a portion of the net proceeds we receive from this offering to repay outstanding indebtedness under our $150.0 million revolving credit facility, which was approximately $14.8 million as of March 31, 2019. We intend to use the remaining net proceeds to us from this offering for acquisitions of, or investments in, technologies, solutions or businesses that complement our business and for other general corporate purposes, including working capital, developing and building an addition adjacent to our corporate headquarters facilities and related real estate development matters, sales and marketing activities, general and administrative matters and capital expenditures. We do not have any agreements or binding commitments for any such acquisitions or investments at this time.

As of March 31, 2019, we had approximately $14.8 million outstanding under our revolving credit facility provided for under our 2017 amended and restated credit agreement with JPMorgan Chase Bank, N.A., as administrative agent, and a syndicate of lenders. Borrowings under the Credit Agreement bear interest at a rate per annum equal to an agreed upon applicable margin plus, at our option, either the alternate base rate (defined as the greatest of (i) the Prime Rate (as defined in our revolving credit facility) in effect on such day, (ii) the NYFRB Rate (as defined in our revolving credit facility) in effect on such day plus 1/2 of 1.00% or (iii) the Adjusted LIBO Rate (as defined in our revolving credit facility) for a one month interest period ending on such day (or if such day is not a business day, the immediately preceding business day) plus 1.00%) or the Adjusted LIBO Rate. The applicable margin for borrowings under the revolving credit facility is based on our most recently tested consolidated total net leverage ratio and will vary from (a) in the case of Eurodollar loans, 1.25% to 2.00%, and (b) in the case of ABR Loans (as defined in our revolving credit facility) or swingline loans, 0.25% to 1.00%. We pay a commitment fee ranging from 0.15% to 0.30% on the unused portion of the revolving credit facility.

Affiliates of J.P. Morgan Securities LLC and RBC Capital Markets, LLC are lenders under our revolving credit facility and will receive their pro rata portions of any amounts repaid under such facility from the proceeds of this offering. See “Underwriting (conflicts of interest)—Conflicts of interest.”

We will have broad discretion over the uses of the net proceeds in this offering. Pending these uses, we may invest the net proceeds from this offering in short-term, investment-grade interest-bearing securities such as money market accounts, certificates of deposit, commercial paper and guaranteed obligations of the U.S. government.

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Market information for our Class A common stock

Our Class A common stock is listed on the Nasdaq Global Select Market under the symbol “ALTR.” On June 3, 2019, the last reported sale price of our Class A common stock on the Nasdaq Global Select Market was $36.82 per share. As of April 29, 2019, we had approximately 84 registered stockholders of record of our Class A common stock and four registered stockholders of record of our Class B common stock, and we believe a substantially greater number of beneficial owners who hold shares of Class A common stock through brokers, banks or other nominees through the facilities of DTC.

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Dividend policy

We have never declared or paid any cash dividends on our common stock, including our Class A common stock. We currently intend to retain all available funds and any future earnings for use in the operation of our business and do not anticipate paying any dividends on our Class A common stock in the foreseeable future. The terms of our revolving credit facility also restrict our ability to pay dividends, and we may also enter into credit agreements or other borrowing arrangements in the future that will restrict our ability to declare or pay cash dividends on our capital stock. Any future determination regarding the declaration and payment of dividends, if any, will be at the discretion of our board of directors and will depend on then-existing conditions, including our financial condition, operating results, contractual restrictions, capital requirements, business prospects, and other factors our board of directors may deem relevant. There can be no assurance that any dividends will be paid in the future.

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