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

Prospectus

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.

S-i

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.

S-ii

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:

S-iii

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.

S-iv

S-1

S-2

S-3

S-4

S-5

S-6

S-7

S-8

S-9

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.

S-10

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

S-11

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

S-12

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

S-13

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.

S-14

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

S-15

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.

S-16

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

S-17

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

S-18

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:

S-19

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.

S-20

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.

S-21

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

S-22

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

S-23

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:

S-24

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.

S-25

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.

S-26

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.

S-27

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.

S-28

Capitalization

The following table sets forth our consolidated cash and cash equivalents and capitalization as of March 31, 2019:

You should read this table in conjunction with “Use of proceeds” as well as our “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and our consolidated financial statements, including the related notes, included in our Quarterly Report on Form 10-Q for the quarter ended March 31, 2019, which is incorporated by reference herein.

S-29

S-30

Description of notes

We will issue the     % Convertible Senior Notes due 2024 (the “notes”) under a base indenture (the “base indenture”) and a supplemental indenture with respect to the notes (the “supplemental indenture” and together with the base indenture, the “indenture”), each to be dated as of the date of initial issuance of the notes, and in each case between us and U.S. Bank National Association, as trustee (the “trustee”). This description of the notes supplements and, to the extent it is inconsistent, replaces the description of the general provisions of the notes and the base indenture in the accompanying prospectus. The terms of the notes include those expressly set forth in the indenture and those made part of the indenture by reference to the Trust Indenture Act of 1939, as amended (the “Trust Indenture Act”).

You may request a copy of the indenture from us as described under “Where you can find more information.”

The following description is a summary of the material provisions of the notes and the indenture and does not purport to be complete. This summary is subject to and is qualified by reference to all of the provisions of the notes and the indenture, including the definitions of certain terms used in the indenture. We urge you to read these documents because they, and not this description, define your rights as a holder of the notes.

For purposes of this description, references to “we,” “our” and “us” refer only to Altair Engineering Inc. and not to its subsidiaries. We use the terms “Class A common stock” in this prospectus supplement to refer to our Class A common stock, par value $0.0001 per share, and “Class B common stock” to refer to our Class B common stock, par value $0.0001 per share.

General

The notes will:

S-31

Subject to satisfaction of certain conditions and during the periods described below, the notes may be converted at an initial conversion rate of                 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 is subject to adjustment if certain events occur.

We will settle conversions of notes by paying or delivering, 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 under “—Conversion rights—Settlement upon conversion.” You will not receive any separate cash payment for interest, if any, accrued and unpaid to the conversion date except under the limited circumstances described below.

The indenture will not limit the amount of debt, including secured debt, that may be issued by us or our subsidiaries under the indenture or otherwise. The indenture will not contain any financial covenants and will not prevent us from paying dividends or issuing or repurchasing our securities or from repaying indebtedness. Other than restrictions described under “—Fundamental change permits holders to require us to repurchase notes” and “—Consolidation, merger and sale of assets” below and except for the provisions set forth under “—Conversion rights—Increase in conversion rate upon conversion upon a make-whole fundamental change or during a redemption period,” the indenture will not contain any covenants or other provisions designed to afford holders of the notes protection in the event of a highly leveraged transaction involving us or in the event of a decline in our credit rating as the result of a takeover, recapitalization, highly leveraged transaction or similar restructuring involving us that could adversely affect such holders.

We may, without the consent of, or notice to, the holders, reopen the indenture for the notes and issue additional notes under the indenture with the same terms as the notes offered hereby (other than differences in the issue date, the issue price and interest accrued prior to the issue date of such additional notes) in an unlimited aggregate principal amount; provided that if any such additional notes are not fungible with the notes initially offered hereby for U.S. federal income tax purposes, such additional notes will have one or more separate CUSIP numbers.

We do not intend to list the notes on any securities exchange or any automated dealer quotation system.

Except to the extent the context otherwise requires, we use the term “notes” in this prospectus supplement to refer to each $1,000 principal amount of notes. References in this prospectus supplement to a “holder” or “holders” of notes that are held through The Depository Trust Company (“DTC”) are references to owners of beneficial interests in such notes, unless the context otherwise requires. However, we and the trustee will treat the person in whose name the notes are registered (Cede & Co., in the case of notes held through DTC) as the owner of such notes for all purposes. References herein to the “close of business” refer to 5:00 p.m., New York City time, and to the “open of business” refer to 9:00 a.m., New York City time.

Purchase and cancellation

We will cause all notes surrendered for payment, repurchase (including as described below), redemption, registration of transfer or exchange or conversion, if surrendered to any person that we control other than the trustee (including any of our agents, subsidiaries or affiliates), to be delivered to the trustee for cancellation. All notes delivered to the trustee shall be cancelled promptly by the trustee. Except for notes surrendered for transfer or exchange, no notes shall be authenticated in exchange for any notes cancelled as provided in the indenture.

S-32

We may, to the extent permitted by law, and directly or indirectly (regardless of whether such notes are surrendered to us), repurchase notes in the open market or otherwise, whether by us or our subsidiaries or through a private or public tender or exchange offer or through counterparties to private agreements, including by cash-settled swaps or other derivatives, in each case, without prior written notice to or consent of the holders of the notes. We will cause any notes so repurchased (other than notes repurchased pursuant to cash-settled swaps or other derivatives) to be surrendered to the trustee for cancellation, and they will no longer be considered “outstanding” under the indenture upon their repurchase, and upon receipt of a written order from us, the trustee will cancel all notes so surrendered.

Payments on the notes; paying agent and registrar; transfer and exchange

We will pay or cause the paying agent to pay the principal of, and interest on, notes in global form registered in the name of or held by DTC or its nominee by wire transfer in immediately available funds to DTC or its nominee, as the case may be, as the registered holder of such global note.

We will pay or cause the paying agent to pay the principal of any certificated notes at the office or agency designated by us for that purpose. We have initially designated the trustee as our paying agent and registrar and its corporate trust office located in the United States of America as a place where notes may be presented for payment or for registration of transfer. We may, however, change the paying agent or registrar without prior notice to the holders of the notes, and we may act as paying agent or registrar. Interest on certificated notes will be payable (i) to holders having an aggregate principal amount of $5,000,000 or less, by check mailed to the holders of these notes and (ii) to holders having an aggregate principal amount of more than $5,000,000, either by check mailed to each holder or, upon application by such a holder to the registrar not later than the relevant regular record date, by wire transfer in immediately available funds to that holder’s account within the United States if such holder has provided the trustee or paying agent (if other than the trustee) with the requisite information necessary to make such wire transfer, which application shall remain in effect until the holder notifies, in writing, the registrar of the notes to the contrary.

A holder of notes may transfer or exchange notes at the office of the registrar in accordance with the indenture. The registrar and the trustee may require a holder, among other things, to furnish appropriate endorsements and transfer documents. No service charge will be imposed by us, the trustee or the registrar for any registration of transfer or exchange of notes, but we may require a holder to pay a sum sufficient to cover any transfer tax or other similar governmental charge required by law or permitted by the indenture. We are not required to transfer or exchange any note selected for redemption or surrendered for conversion or required repurchase upon a fundamental change. A holder of a beneficial interest in a note in global form may transfer or exchange such beneficial interest in accordance with the indenture and the applicable procedures of DTC. See “—Book-entry, settlement and clearance.”

The registered holder of a note will be treated as its owner for all purposes.

Interest

The notes will bear cash interest at a rate of     % per year until maturity. Interest on the notes will accrue from June     , 2019 or from the most recent date on which interest has been paid or duly provided for. Interest will be payable semiannually in arrears on June 1 and December 1 of each year, beginning on December 1, 2019.

Interest will be paid to the person in whose name a note is registered at the close of business on May 15 or November 15 (whether or not a business day), as the case may be, immediately preceding the relevant interest payment date (each, a “regular record date”). Interest on the notes will be computed on the basis of a 360-day year composed of twelve 30-day months and, for partial months, on the basis of the number of days actually elapsed in a 30-day month.

S-33

If any interest payment date, the maturity date or any earlier required repurchase date upon a fundamental change of a note falls on a day that is not a business day, the required payment will be made on the next succeeding business day with the same force and effect as if made on the relevant scheduled payment date, and no interest on such payment will accrue in respect of the delay. The term “business day” means, with respect to any note, any day other than a Saturday, a Sunday or a day on which the Federal Reserve Bank of New York is authorized or required by law or executive order to close or be closed.

Unless the context otherwise requires, all references to interest in this prospectus supplement include additional interest, if any, payable at our election as the sole remedy relating to the failure to comply with our reporting obligations as described under “—Events of default.”

Ranking

The notes will be our general unsecured obligations that rank senior in right of payment to all of our indebtedness that is expressly subordinated in right of payment to the notes. The notes will rank equal in right of payment with all of our liabilities that are not so subordinated. The notes will effectively rank 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. Although our revolving credit facility currently contains such limitations, the indenture governing the notes will not by itself limit our ability to incur additional indebtedness in the future, including secured indebtedness, and such indebtedness may be substantial. In the event of our bankruptcy, liquidation, reorganization or other winding up, our assets that secure secured debt will be available to pay obligations on the notes only after all indebtedness under such secured debt has been repaid in full from such assets. We advise you that there may not be sufficient assets remaining to pay amounts due on any or all of the notes then outstanding.

The notes will rank structurally junior to all indebtedness and other liabilities of our subsidiaries (including trade payables). A substantial portion of our operations is conducted through our subsidiaries. The notes will not be guaranteed by any of our current or future subsidiaries. Our subsidiaries are separate and distinct legal entities and have no obligation, contingent or otherwise, to pay amounts due with respect to the notes or to make any funds available therefor, whether by dividends, loans or other payments. Our right to receive any assets of any of our subsidiaries upon such subsidiary’s bankruptcy, liquidation or reorganization, and, therefore, the right of the holders of notes to participate in those assets, will be subject to prior claims of creditors of the subsidiary, including trade creditors, and such subsidiary may not have sufficient assets remaining to make any payments to us as a shareholder or otherwise. We advise you that there may not be sufficient assets remaining to pay amounts due on any or all the notes then outstanding.

As of March 31, 2019, our total consolidated indebtedness was approximately $16.2 million, of which an aggregate of approximately $14.8 million was secured indebtedness of ours. As of March 31, 2019, our subsidiaries had approximately $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 from this offering as described in “Use of proceeds,” our total consolidated indebtedness as of March 31, 2019 would have been $176.4 million.

The ability of our subsidiaries to pay dividends and make other payments to us may be restricted by, among other things, our future debt instruments, applicable corporate and other laws and regulations as well as agreements to which our subsidiaries may become a party. We may not be able to pay the cash portion of any settlement amount upon conversion of the notes, or to pay cash for the fundamental change repurchase price if a holder requires us to repurchase notes upon a fundamental change as described below. See “Risk factors—

S-34

Risks related to the notes—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.”

Optional redemption

No “sinking fund” is provided for the notes, which means we are not required to redeem or retire the notes periodically. Prior to June 6, 2022, the notes will not be redeemable. On or after June 6, 2022, we may redeem all or part of the notes, at our option, if the last reported sale price (as defined under “—Conversion rights—Settlement upon conversion”) 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 the holders written notice of redemption (a “redemption notice date”). In the case of any optional redemption, we will provide not less than 60 nor more than 75 scheduled trading days’ written notice before the redemption date (provided that if we elect physical settlement (as defined under “—Conversion rights—Settlement upon conversion”) for conversions that occur during the related redemption period, we may provide not less than 10 nor more than 30 scheduled trading days’ written notice) to the trustee, the conversion agent (if other than the trustee), the paying agent and each holder of notes, and we will redeem the notes at a redemption price equal to 100% of the principal amount of such notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. Any notes redeemed by us will be paid for in cash. The redemption date must be a business day and we may not specify a redemption date that falls on or after December 1, 2023.

Notwithstanding the foregoing, if we set a redemption date between a regular record date and the corresponding interest payment date, we will not pay accrued interest to any holder of notes to be redeemed, and will instead pay the full amount of the relevant interest payment on such interest payment date to the holder of record on such regular record date, and the redemption price will be 100% of the principal amount of the notes to be redeemed.

With respect to any notes that are converted during a redemption period as described under “—Conversion Rights—General,” we will, under certain circumstances, increase the conversion rate for the notes so surrendered for conversion by a number of additional shares as described under “—Conversion rights—Increase in conversion rate upon conversion upon a make-whole fundamental change or during a redemption period.”

If we decide to redeem fewer than all of the outstanding notes, the notes to be redeemed will be selected according to DTC’s applicable procedures, in the case of notes represented by a global note, or, in the case of notes in certificated form, the trustee shall select, pro rata or by lot or in such other manner as it shall deem appropriate and fair, notes to be redeemed in whole or in part.

If the trustee selects a portion of your notes for redemption and you convert a portion of such notes, the converted portion will be deemed to be from the portion selected for redemption.

In the event of any redemption in part, we will not be required to register the transfer of or exchange any note so selected for redemption, in whole or in part, except the unredeemed portion of any such note being redeemed in part.

No notes may be redeemed if the principal amount of the notes has been accelerated, and such acceleration has not been rescinded, on or prior to the redemption date (except in the case of an acceleration resulting from a default by us in the payment of the redemption price with respect to such notes).

S-35

Conversion rights

General

Prior to the close of business on the business day immediately preceding December 1, 2023, the notes will be convertible only upon satisfaction of one or more of the conditions described under the headings “—Conversion upon satisfaction of sale price condition,” “—Conversion upon satisfaction of trading price condition,” “—Conversion upon redemption,” and “—Conversion upon 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 all or any portion of their notes at the conversion rate at any time irrespective of the foregoing conditions.

The conversion rate for the notes 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 is subject to adjustment if certain events occur. The conversion price at any given time will be computed by dividing $1,000 by the applicable conversion rate at such time. Accordingly, an adjustment to the conversion rate will result in a corresponding (but inverse) adjustment to the conversion price.

Upon conversion of a note, we will satisfy our conversion obligation by paying or delivering, 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, all as set forth below under “—Settlement upon conversion.” If we satisfy our conversion obligation solely in cash or through payment and delivery, as the case may be, of a combination of cash and shares of our Class A common stock, the amount of cash and shares of Class A common stock, if any, due upon conversion will be based on a daily conversion value (as defined below) calculated on a proportionate basis for each trading day in a 50 trading day observation period (as defined below under “—Settlement upon conversion”). The trustee will initially act as the conversion agent.

A holder may convert fewer than all of such holder’s notes so long as the notes converted are in minimum denominations of $1,000 or integral multiples of $1,000 in excess thereof.

If we call notes for redemption, a holder of notes may convert all or any portion of its notes only until the close of business on the scheduled trading day immediately preceding the redemption date unless we fail to pay the redemption price (in which case a holder of notes may convert such notes until the redemption price has been paid or duly provided for). If a holder elects to convert notes from, and including, the redemption notice date until the close of business on the scheduled trading day immediately preceding the related redemption date (any such period, a “redemption period”), we will, under certain circumstances, increase the conversion rate for the notes as described under “—Increase in conversion rate upon conversion upon a make-whole fundamental change or during a redemption period.” If a holder of notes has submitted notes for purchase upon a fundamental change, the holder may convert those notes only if that holder first validly withdraws its fundamental change purchase notice.

Upon conversion, you will not receive any separate cash payment for accrued and unpaid interest, if any, except as described below, and we will not adjust the conversion rate for any accrued and unpaid interest on the notes. We will not issue fractional shares of our Class A common stock upon conversion of notes. Instead, we will pay cash in lieu of delivering any fractional share as described under “—Settlement upon conversion.” Our payment and delivery, as the case may be, to you of the cash, shares of our Class A common stock or a combination thereof, as the case may be, into which a note is convertible will be deemed to satisfy in full our obligation to pay:

S-36

As a result, accrued and unpaid interest, if any, to, but excluding, the relevant conversion date will be deemed to be paid in full rather than cancelled, extinguished or forfeited. Upon a conversion of notes into a combination of cash and shares of our Class A common stock, accrued and unpaid interest will be deemed to be paid first out of the cash paid upon such conversion.

Notwithstanding the immediately preceding paragraph, if notes are converted after the close of business on a regular record date for the payment of interest and prior to the open of business on the corresponding interest payment date, holders of such notes at the close of business on such regular record date will receive the full amount of interest payable on such notes on the corresponding interest payment date notwithstanding the conversion. Notes surrendered for conversion during the period from the close of business on any regular record date to the open of business on the immediately following interest payment date, however, must be accompanied by funds equal to the amount of interest payable on the notes so converted on the corresponding interest payment date (regardless of whether the converting holder was the holder of record on such regular record date); provided that no such payment need be made:

Therefore, for the avoidance of doubt, all record holders on the regular record date immediately preceding the maturity date, any redemption date and any fundamental change repurchase date described in the bullets in the preceding paragraph will receive and retain the full interest payment due on the maturity date or other applicable interest payment date regardless of whether their notes have been converted following such regular record date.

If a holder converts notes, we will pay any documentary, stamp or similar issue or transfer tax due on any issuance of any shares of our Class A common stock upon the conversion, unless the tax is due because the holder requests such shares to be issued in a name other than the holder’s name, in which case the holder will pay that tax.

Holders may surrender their notes for conversion only under the following circumstances:

Conversion upon satisfaction of sale price condition

Prior to the close of business on the business day immediately preceding December 1, 2023, a holder may surrender all or any portion of its notes for conversion at any time 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 the Class A common stock for at least 20 trading days (whether or not consecutive) during the 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.

The “last reported sale price” of our Class A common stock on any date means the closing sale price per share (or if no closing sale price is reported, the average of the bid and ask prices or, if more than one in either case,

S-37

the average of the average bid and the average ask prices) on that date as reported in composite transactions for the principal U.S. national or regional securities exchange on which our Class A common stock is traded. If our Class A common stock is not listed for trading on a U.S. national or regional securities exchange on the relevant date, the “last reported sale price” will be the last quoted bid price per share for our Class A common stock in the over-the-counter market on the relevant date as reported by OTC Markets Group Inc. or a similar organization. If our Class A common stock is not so quoted, the “last reported sale price” will be the average of the mid-point of the last bid and ask prices per share for our Class A common stock on the relevant date from each of at least three nationally recognized independent investment banking firms selected by us for this purpose. The “last reported sale price” will be determined without regard to after-hours trading or any other trading outside of regular trading session hours.

Except for determining amounts due upon conversion, “trading day” means a day on which (i) trading in our Class A common stock (or other security for which a closing sale price must be determined) generally occurs on The Nasdaq Global Select Market or, if our Class A common stock (or such other security) is not then listed on The Nasdaq Global Select Market, on the principal other U.S. national or regional securities exchange on which our Class A common stock (or such other security) is then listed or, if our Class A common stock (or such other security) is not then listed on a U.S. national or regional securities exchange, on the principal other market on which our Class A common stock (or such other security) is then traded, and (ii) a last reported sale price for our Class A common stock (or closing sale price for such other security) is available on such securities exchange or market. If our Class A common stock (or such other security) is not so listed or traded, “trading day” means a “business day.”

Conversion upon satisfaction of trading price condition

Prior to the close of business on the business day immediately preceding December 1, 2023, a holder of notes may surrender all or any portion of its notes for conversion at any time during the five business day period after any five consecutive trading day period (the “measurement period”) in which the “trading price” per $1,000 principal amount of notes, as determined following a request by a holder of notes in accordance with the procedures described below, 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 (the “trading price condition”).

The “trading price” of the notes on any date of determination means the average of the secondary market bid quotations obtained by the bid solicitation agent for $2,000,000 principal amount of notes at approximately 3:30 p.m., New York City time, on such determination date from three independent nationally recognized securities dealers we select for this purpose; provided that if three such bids cannot reasonably be obtained by the bid solicitation agent but two such bids are obtained, then the average of the two bids shall be used, and if only one such bid can reasonably be obtained by the bid solicitation agent, that one bid shall be used. If the bid solicitation agent cannot reasonably obtain at least one bid for $2,000,000 principal amount of notes from a nationally recognized securities dealer, then the trading price per $1,000 principal amount of notes will be deemed to be less than 98% of the product of the last reported sale price of our Class A common stock and the conversion rate. If (x) we are not acting as bid solicitation agent, and we do not, when we are required to, instruct the bid solicitation agent in writing to obtain bids, or if we give such written instruction to the bid solicitation agent, and the bid solicitation agent fails to obtain such bids, or (y) we are acting as bid solicitation agent and we fail to obtain such bids, then, in either case, the trading price per $1,000 principal amount of notes will be deemed to be less than 98% of the product of the last reported sale price of our Class A common stock and the conversion rate on each trading day of such failure.

The bid solicitation agent (if other than us) shall have no obligation to solicit bids as described above unless we have requested such solicitation in writing; and we shall have no obligation to make such request (or, if we are

S-38

acting as bid solicitation agent, we shall have no obligation to solicit such bids) unless a holder of at least $1,000,000 aggregate principal amount of notes provides us with reasonable evidence that the trading price per $1,000 principal amount of notes would be less than 98% of the product of the last reported sale price of our Class A common stock and the conversion rate. At such time, we shall instruct the bid solicitation agent (if other than us) to solicit, or if we are acting as bid solicitation agent, we shall solicit, such bids beginning on the next trading day and on each successive trading day until the trading price per $1,000 principal amount of notes is greater than or equal to 98% of the product of the last reported sale price of our Class A common stock and the conversion rate and we shall instruct the three independent nationally recognized securities dealers to deliver bids to the bid solicitation agent. We will determine the trading price per $1,000 principal amount of the notes for each trading day in accordance with the bids so solicited. If the trading price condition has been met, we will so notify in writing the holders, the trustee and the conversion agent (if other than the trustee) on or within one business day of such determination. If, at any time after the trading price condition has been met, the trading price per $1,000 principal amount of notes is greater than or equal to 98% of the product of the last reported sale price of our Class A common stock and the conversion rate for such trading day, we will so notify the holders, the trustee and the conversion agent (if other than the trustee) in writing that the trading price condition is no longer met and thereafter neither we nor the bid solicitation agent (if other than us) shall be required to solicit bids again until another qualifying request is made as provided above.

We will initially act as the bid solicitation agent for the notes.

Conversion upon notice of redemption

If we call any or all of the notes for redemption prior to the close of business on the business day immediately preceding December 1, 2023, holders may convert all or any portion of their notes at any time prior to the close of business on the scheduled trading day prior to the redemption date, even if the notes are not otherwise convertible at such time. After that time, the right to convert such notes on account of our delivery of a notice of redemption will expire, unless we default in the payment of the redemption price, in which case a holder of notes may convert all or any portion of its notes until the redemption price has been paid or duly provided for.

Conversion upon specified corporate events

Certain distributions

If, prior to the close of business on the business day immediately preceding December 1, 2023, we elect to:

S-39

then, in either case, we must notify in writing the holders of the notes (with a copy to the trustee and the conversion agent (if other than the trustee) (such notification, the “Certain Distributions Notification”) (x) at least 60 scheduled trading days prior to or (y) if in the Certain Distributions Notification we elect physical settlement (as defined under “—Settlement upon conversion”) in respect of any conversions with conversion dates that occur after delivery to the holders of the Certain Distributions Notification until the Certain Distributions Conversion Period End Date (as defined below), at least 10 scheduled trading days prior to, in either case, the ex-dividend date for such issuance or distribution. Once we have given such notice, holders may surrender all or any portion of their notes for conversion at any time until the earlier of the close of business on the business day immediately preceding the ex-dividend date for such issuance or distribution and our announcement that such issuance or distribution will not take place, even if the notes are not otherwise convertible at such time (such earlier date and time, the “Certain Distributions Conversion Period End Date”).

Holders of the notes may not convert their notes pursuant to this provision if they participate (other than in the case of a share split or share combination), at the same time and upon the same terms as holders of our Class A common stock and solely as a result of holding the notes, in any of the transactions described above without having to convert their notes as if they held a number of shares of Class A common stock equal to the applicable conversion rate, multiplied by the principal amount (expressed in thousands) of notes held by such holder.

Certain corporate events

If (i) a transaction or event that constitutes a (x) “fundamental change” (as defined under “—Fundamental change permits holders to require us to repurchase notes”) or (y) a “make-whole fundamental change” (as defined under “—Increase in conversion rate upon conversion upon a make-whole fundamental change or during a redemption period”) occurs prior to the close of business on the business day immediately preceding December 1, 2023, regardless of whether a holder has the right to require us to repurchase the notes as described under “—Fundamental change permits holders to require us to repurchase notes,” or (ii) we are a party to a share exchange event (as defined under “— Recapitalizations, reclassifications and changes of our Class A common stock”) (other than a share exchange event that is solely for the purpose of changing our jurisdiction of organization that (x) does not constitute a fundamental change or a make-whole fundamental change and (y) results in a reclassification, conversion or exchange of outstanding shares of our Class A common stock solely into shares of common stock of the surviving entity and such common stock becomes reference property for the notes) that occurs prior to the close of business on the business day immediately preceding December 1, 2023 (each such fundamental change, make-whole fundamental change or share exchange event, a “corporate event”), then, in each case, all or any portion of a holder’s notes may be surrendered for conversion at any time from or after the effective date of such corporate event until the earlier of (a) 35 trading days after the effective date of such corporate event or, if such corporate event also constitutes a fundamental change, until the close of business on the business day immediately preceding the related fundamental change repurchase date and (b) the business day immediately preceding the maturity date. We will notify holders, the trustee and the conversion agent (if other than the trustee) in writing as promptly as practicable following the date we publicly announce such corporate event but in no event later than the effective date of such corporate event.

Conversions on or after December 1, 2023

On or after December 1, 2023, a holder may convert all or any portion of its notes at any time prior to the close of business on the business day immediately preceding the maturity date regardless of the foregoing conditions.

S-40

Conversion procedures

If you hold a beneficial interest in a global note, to convert you must comply with DTC’s procedures for converting a beneficial interest in a global note and, if required, pay funds equal to interest payable on the next interest payment date to which you are not entitled and, if required, pay all transfer or similar taxes, if any. As such, if you are a beneficial owner of the notes, you must allow for sufficient time to comply with DTC’s procedures if you wish to exercise your conversion rights.

If you hold a certificated note, to convert you must:

We will pay any documentary, stamp or similar issue or transfer tax on the issuance of any shares of our Class A common stock upon conversion of the notes, unless the tax is due because the holder requests such shares to be issued in a name other than the holder’s name, in which case the holder will pay the tax.

We refer to the date you comply with the relevant procedures for conversion described above as the “conversion date.”

If a holder has already delivered a repurchase notice as described under “—Fundamental change permits holders to require us to repurchase notes” with respect to a note, the holder may not surrender that note for conversion until the holder has withdrawn the repurchase notice in accordance with the relevant provisions of the indenture. If a holder submits its notes for required repurchase, the holder’s right to withdraw the fundamental change repurchase notice and convert the notes that are subject to repurchase will terminate at the close of business on the business day immediately preceding the relevant fundamental change repurchase date.

Settlement upon conversion

Upon conversion, we may choose to pay or deliver, as the case may be, either cash (“cash settlement”), shares of our Class A common stock (“physical settlement”) or a combination of cash and shares of our Class A common stock (“combination settlement”), as described below. We refer to each of these settlement methods as a “settlement method.”

All conversions for which the relevant conversion date occurs on or after December 1, 2023 or during a redemption period, will be settled using the same settlement method. Except for any conversions for which the relevant conversion date occurs during a redemption period and any conversions for which the relevant conversion date occurs on or after December 1, 2023, we will use the same settlement method for all conversions with the same conversion date, but we will not have any obligation to use the same settlement method with respect to conversions with different conversion dates. That is, prior to December 1, 2023 and other than during a redemption period, we may choose for notes converted on one conversion date to settle through physical settlement, and choose for notes converted on another conversion date to settle through cash settlement or combination settlement.

S-41

If we elect a settlement method, we will inform in writing holders so converting, the trustee and the conversion agent (if other than the trustee) of the settlement method we have selected no later than the close of business on the trading day immediately following the related conversion date (or in the case of any conversion for which the relevant conversion date occurs (i) during a redemption period as described under “—Optional redemption,” in the related notice of redemption or (ii) on or after December 1, 2023, no later than the close of business on the business day immediately preceding December 1, 2023). If we do not timely elect a settlement method as described in the preceding sentence, we will no longer have the right to elect cash settlement or physical settlement for such conversion or during such period and we will be deemed to have elected combination settlement in respect of our conversion obligation, as described below, and the specified dollar amount (as defined below) per $1,000 principal amount of notes will be equal to $1,000. If we timely elect combination settlement, but we do not timely notify converting holders, the trustee and the conversion agent (if other than the trustee) of the specified dollar amount per $1,000 principal amount of notes to be converted, such specified dollar amount will be deemed to be $1,000. Notwithstanding anything to the contrary in the foregoing, we will be permitted to irrevocably elect “physical settlement” in any Certain Distributions Notification as described above under “Conversion rights—Conversion upon specified corporate events—Certain distributions” and any such election would be applicable to conversions with conversion dates that occur after delivery to the holders of the Certain Distributions Notification until the Certain Distributions Conversion Period End Date. It is our current intent and policy to settle conversions of the notes through combination settlement with a specified dollar amount per $1,000 principal amount of notes of $1,000.

Settlement amounts will be computed as follows:

The “daily settlement amount,” for each of the 50 consecutive trading days during the observation period, shall consist of:

The “daily conversion value” means, for each of the 50 consecutive trading days during the observation period, 2.0% of the product of (1) the conversion rate on such trading day and (2) the daily VWAP for such trading day.

The “daily VWAP” means the per share volume-weighted average price as displayed under the heading “Bloomberg VWAP” on Bloomberg page “ALTR <equity> AQR” (or its equivalent successor if such page is not

S-42

available) in respect of the period from the scheduled open of trading until the scheduled close of trading of the primary trading session on such trading day (or if such volume-weighted average price is unavailable, the market value of one share of our Class A common stock on such trading day determined, using a volume-weighted average method, by a nationally recognized independent investment banking firm retained for this purpose by us). The “daily VWAP” will be determined without regard to after-hours trading or any other trading outside of the regular trading session trading hours.

The “observation period” with respect to any note surrendered for conversion means:

For the purposes of determining amounts due upon conversion only, “trading day” means a day on which (i) there is no “market disruption event” (as defined below) and (ii) trading in our Class A common stock generally occurs on The Nasdaq Global Select Market or, if our Class A common stock is not then listed on The Nasdaq Global Select Market, on the principal other U.S. national or regional securities exchange on which our Class A common stock is then listed or, if our Class A common stock is not then listed on a U.S. national or regional securities exchange, on the principal other market on which our Class A common stock is then listed or admitted for trading. If our Class A common stock is not so listed or admitted for trading, “trading day” means a “business day.”

“Scheduled trading day” means a day that is scheduled to be a trading day on the principal U.S. national or regional securities exchange or market on which our Class A common stock is listed or admitted for trading. If our Class A common stock is not so listed or admitted for trading, “scheduled trading day” means a “business day.”

For the purposes of determining amounts due upon conversion, “market disruption event” means (i) a failure by the primary U.S. national or regional securities exchange or market on which our Class A common stock is listed or admitted for trading to open for trading during its regular trading session or (ii) the occurrence or existence prior to 1:00 p.m., New York City time, on any scheduled trading day for our Class A common stock for more than one half-hour period in the aggregate during regular trading hours of any suspension or limitation imposed on trading (by reason of movements in price exceeding limits permitted by the relevant stock exchange or otherwise) in our Class A common stock or in any options contracts or futures contracts relating to our Class A common stock.

Except as described under “—Increase in conversion rate upon conversion upon a make-whole fundamental change or during a redemption period” and “—Recapitalizations, reclassifications and changes of our Class A common stock,” we will deliver the consideration due in respect of conversion on the second business day immediately following the relevant conversion date, if we elect to satisfy our conversion obligation through physical settlement, or on the second business day immediately following the last trading day of the relevant observation period, in the case of any other settlement method.

S-43

We will pay cash in lieu of delivering any fractional share of Class A common stock issuable upon conversion based on the daily VWAP for the relevant conversion date (in the case of physical settlement) or based on the daily VWAP for the last trading day of the relevant observation period (in the case of combination settlement).

Each conversion will be deemed to have been effected as to any notes surrendered for conversion on the conversion date; provided, however, that the person in whose name any shares of our Class A common stock shall be issuable upon such conversion will be treated as the holder of record of such shares as of the close of business on the conversion date (in the case of physical settlement) or the last trading day of the relevant observation period (in the case of combination settlement).

Exchange in lieu of conversion

When a holder surrenders its notes for conversion, we may, at our election, direct the conversion agent to surrender, on or prior to the trading day immediately following the conversion date, such notes to one or more financial institutions designated by us for exchange in lieu of conversion (an “exchange election”). To accept any notes surrendered for conversion, the designated financial institution must agree to timely pay or deliver, as the case may be, in exchange for such notes, the cash, shares of our Class A common stock, or combination of cash or shares of our Class A common stock that would otherwise be due on conversion as described above under the section titled “—Conversion rights— Settlement upon conversion” (the “conversion consideration”). If we make an exchange election, we will, by the close of business on the trading day following the relevant conversion date, notify in writing the trustee, the conversion agent (if other than the trustee) and the holder surrendering its notes for conversion that we have made the exchange election and will notify the designated financial institution of the settlement method we have elected with respect to such conversion and the relevant deadline for delivery of the conversion consideration.

Any notes exchanged by the designated financial institution will remain outstanding, subject to applicable DTC procedures. If the designated financial institution agrees to accept any notes for exchange but does not timely pay or deliver, as the case may be, the related conversion consideration, or if such designated financial institution does not accept the notes for exchange, we will pay or deliver, as the case may be, the relevant conversion consideration, as, and at the time, required pursuant to the indenture as if we had not made the exchange election.

Our designation of any financial institution to which the notes may be submitted for exchange does not require such financial institution to accept any notes.

Conversion rate adjustments

The conversion rate will be adjusted as described below, except that we will not make any adjustments to the conversion rate if holders of the notes participate (other than in the case of (x) a share split or share combination or (y) a tender or exchange offer), at the same time and upon the same terms as holders of our Class A common stock and solely as a result of holding the notes, in any of the transactions described below without having to convert their notes as if they held a number of shares of Class A common stock equal to the conversion rate, multiplied by the principal amount (expressed in thousands) of notes held by such holder.

S-44

where,

Any adjustment made under this clause (1) shall become effective immediately after the open of business on the ex-dividend date for such dividend or distribution, or immediately after the open of business on the effective date for such share split or share combination, as applicable. If any dividend or distribution of the type described in this clause (1) is declared but not so paid or made, the conversion rate shall be immediately readjusted, effective as of the date our board of directors or a committee thereof determines not to pay such dividend or distribution, to the conversion rate that would then be in effect if such dividend or distribution had not been declared.

where,

S-45

Any increase made under this clause (2) will be made successively whenever any such rights, options or warrants are issued and shall become effective immediately after the open of business on the ex-dividend date for such issuance. To the extent that such rights, options or warrants are not exercised prior to their expiration or shares of our Class A common stock are not delivered after the expiration of such rights, options or warrants, the conversion rate shall be decreased to the conversion rate that would then be in effect had the increase with respect to the issuance of such rights, options or warrants been made on the basis of delivery of only the number of shares of our Class A common stock actually delivered. If such rights, options or warrants are not so issued, the conversion rate shall be decreased to the conversion rate that would then be in effect if such ex-dividend date for such issuance had not occurred.

For the purpose of this clause (2), and for the purpose of the first bullet point under “—Conversion upon specified corporate events—Certain distributions,” in determining whether any rights, options or warrants entitle the holders of our Class A common stock to subscribe for or purchase shares of our Class A common stock at a price per share that is less than such average of the last reported sale prices of our Class A common stock for the 10 consecutive trading day period ending on, and including, the trading day immediately preceding the date of announcement of such issuance, and in determining the aggregate offering price of such shares of Class A common stock, there shall be taken into account any consideration received by us for such rights, options or warrants and any amount payable on exercise or conversion thereof, the value of such consideration, if other than cash, to be determined by our board of directors or a committee thereof.

then the conversion rate will be increased based on the following formula:

where,

S-46

Any increase made under the portion of this clause (3) above will become effective immediately after the open of business on the ex-dividend date for such distribution. If such distribution is not so paid or made, the conversion rate shall be decreased to be the conversion rate that would then be in effect if such distribution had not been declared. Notwithstanding the foregoing, if “FMV” (as defined above) is equal to or greater than “SP₀” (as defined above), in lieu of the foregoing increase, each holder of a note shall receive, in respect of each $1,000 principal amount thereof, at the same time and upon the same terms as holders of our Class A common stock, the amount and kind of our capital stock, evidences of our indebtedness, other assets or property of ours or rights, options or warrants to acquire our capital stock or other securities that such holder would have received if such holder owned a number of shares of Class A common stock equal to the conversion rate in effect on the ex-dividend date for the distribution.

With respect to an adjustment pursuant to this clause (3) where there has been a payment of a dividend or other distribution on our Class A common stock of shares of capital stock of any class or series, or similar equity interest, of or relating to a subsidiary or other business unit, that are, or, when issued, will be, listed or admitted for trading on a U.S. national securities exchange, which we refer to as a “spin-off,” the conversion rate will be increased based on the following formula:

where,

The increase to the conversion rate under the preceding paragraph will occur at the close of business on the last trading day of the valuation period; provided that (x) in respect of any conversion of notes for which physical settlement is applicable, if the relevant conversion date occurs during the valuation period, the reference to “10” in the preceding paragraph shall be deemed replaced with such lesser number of trading days as have elapsed between the ex-dividend date for such spin-off and such conversion date in determining the conversion rate and (y) in respect of any conversion of notes for which cash settlement or combination settlement is applicable, for any trading day that falls within the relevant observation period for such conversion and within the valuation period, the reference to “10” in the preceding paragraph shall be deemed replaced with such lesser number of trading days as have elapsed between the ex-dividend

S-47

date for such spin-off and such trading day in determining the conversion rate as of such trading day of such observation period. If any dividend or distribution that constitutes a spin-off is declared but not so paid or made, the conversion rate shall be immediately decreased, effective as of the date our board of directors or a committee thereof determines not to pay or make such dividend or distribution, to the conversion rate that would then be in effect if such dividend or distribution had not been declared or announced.

where,

Any increase made under this clause (4) shall become effective immediately after the open of business on the ex-dividend date for such dividend or distribution. If such dividend or distribution is not so paid, the conversion rate shall be decreased, effective as of the date our board of directors or a committee thereof determines not to make or pay such dividend or distribution, to be the conversion rate that would then be in effect if such dividend or distribution had not been declared.

Notwithstanding the foregoing, if “C” (as defined above) is equal to or greater than “SP₀” (as defined above), in lieu of the foregoing increase, each holder of a note shall receive, for each $1,000 principal amount of notes it holds, at the same time and upon the same terms as holders of shares of our Class A common stock, the amount of cash that such holder would have received if such holder owned a number of shares of our Class A common stock equal to the conversion rate in effect on the ex-dividend date for such cash dividend or distribution.

S-48

where,

The increase to the conversion rate under the preceding paragraph will occur at the close of business on the 10th trading day immediately following, and including, the trading day next succeeding the date such tender or exchange offer expires; provided that (x) in respect of any conversion of notes for which physical settlement is applicable, if the relevant conversion date occurs during the 10 trading days immediately following, and including, the trading day next succeeding the expiration date of any tender or exchange offer, references to “10” or “10th” in the preceding paragraph shall be deemed replaced with such lesser number of trading days as have elapsed from, and including, the trading day next succeeding such expiration date of such tender or exchange offer to, and including, such conversion date in determining the conversion rate and (y) in respect of any conversion of notes for which cash settlement or combination settlement is applicable, for any trading day that falls within the relevant observation period for such conversion and within the 10 trading days immediately following, and including, the trading day next succeeding the expiration date of any tender or exchange offer, references to “10” or “10th” in the preceding paragraph shall be deemed replaced with such lesser number of trading days as have elapsed from, and including, the trading day next succeeding such expiration date of such tender or exchange offer and such trading day in determining the conversion rate as of such trading day.

In the event that we or one of our subsidiaries is obligated to purchase shares of our Class A common stock pursuant to any such tender offer or exchange offer, but we are, or such subsidiary is, permanently prevented by applicable law from consummating any such purchases, or all such purchases are rescinded, then the conversion rate shall be decreased to be the conversion rate that would then be in effect if such tender offer or exchange offer had not been made or had been made only in respect of the purchases that have been consummated.

Notwithstanding the foregoing, if a conversion rate adjustment becomes effective on any ex-dividend date as described above, and a holder that has converted its notes on or after such ex-dividend date and on or prior to the related record date would be treated as the record holder of shares of our Class A common stock as of the related conversion date as described under “—Settlement upon conversion” based on an adjusted conversion rate for such ex-dividend date, then, notwithstanding the foregoing conversion rate adjustment provisions, the

S-49

conversion rate adjustment relating to such ex-dividend date will not be made for such converting holder. Instead, such holder will be treated as if such holder were the record owner of the shares of our Class A common stock on an unadjusted basis and participate in the related dividend, distribution or other event giving rise to such adjustment.

As used in this section, “ex-dividend date” means the first date on which the shares of our Class A common stock trade on the applicable exchange or in the applicable market, regular way, without the right to receive the issuance, dividend or distribution in question, from us or, if applicable, from the seller of our Class A common stock on such exchange or market (in the form of due bills or otherwise) as determined by such exchange or market, and “effective date” means the first date on which the shares of our Class A common stock trade on the applicable exchange or in the applicable market, regular way, reflecting the relevant share split or share combination, as applicable.

As used in this section, “record date” means, with respect to any dividend, distribution or other transaction or event in which the holders of our Class A common stock (or other applicable security) have the right to receive any cash, securities or other property or in which our Class A common stock (or such other security) is exchanged for or converted into any combination of cash, securities or other property, the date fixed for determination of holders of our Class A common stock (or such other security) entitled to receive such cash, securities or other property (whether such date is fixed by our board of directors or a duly authorized committee thereof, statute, contract or otherwise).

Subject to the applicable listing standards of The Nasdaq Global Select Market, we are permitted to increase the conversion rate of the notes by any amount for a period of at least 20 business days if our board of directors or a committee thereof determines that such increase would be in our best interest. Subject to the applicable listing standards of The Nasdaq Global Select Market, we may also (but are not required to) increase the conversion rate to avoid or diminish income tax to holders of our Class A common stock or rights to purchase shares of our Class A common stock in connection with a dividend or distribution of shares (or rights to acquire shares) or similar event.

A holder may, in some circumstances, including a distribution of cash dividends to holders of our shares of Class A common stock, be deemed to have received a distribution subject to U.S. federal income tax as a result of an adjustment or the nonoccurrence of an adjustment to the conversion rate. For a discussion of the U.S. federal income tax treatment of an adjustment to the conversion rate, see “Material U.S. federal income tax considerations.”

If we have a rights plan in effect upon conversion of the notes into Class A common stock, you will receive, in addition to any shares of Class A common stock received in connection with such conversion, the rights under the rights plan. However, if, prior to any conversion, the rights have separated from the shares of Class A common stock in accordance with the provisions of the applicable rights plan, the conversion rate will be adjusted at the time of separation as if we distributed to all or substantially all holders of our Class A common stock, shares of our capital stock, evidences of indebtedness, assets, property, rights, options or warrants as described in clause (3) above, subject to readjustment in the event of the expiration, termination or redemption of such rights.

Except as stated herein, we will not adjust the conversion rate for the issuance of shares of our Class A common stock or any securities convertible into or exchangeable for shares of our Class A common stock or the right to purchase shares of our common stock or such convertible or exchangeable securities. For example, the conversion rate will not be adjusted:

S-50

If an adjustment to the conversion rate otherwise required by the provisions described above would result in a change of less than 1% to the conversion rate, then, notwithstanding the foregoing, we may, at our election, defer and carry forward such adjustment, except that all such deferred adjustments must be given effect immediately upon the earliest to occur of the following: (i) when all such deferred adjustments would result in an aggregate change of at least 1% to the conversion rate; (ii) the conversion date of (if physical settlement applies to such conversion), or each trading day of the applicable observation period for (if cash settlement or combination settlement applies to such conversion), any note; (iii) the date a fundamental change or make-whole fundamental change occurs; and (iv) December 1, 2023. The provisions described in the preceding sentence are referred to as the “1% provision.”

Adjustments to the conversion rate will be calculated to the nearest 1/10,000th of a share.

Recapitalizations, reclassifications and changes of our Class A common stock

In the case of:

in each case, as a result of which our Class A common stock would be converted into, or exchanged for, stock, other securities, other property or assets (including cash or any combination thereof) (any such event, a “share exchange event”), then, at the effective time of the share exchange event, we or the successor or acquiring corporation, as the case may be, will execute with the trustee a supplemental indenture, without the consent of holders, providing that at and after the effective time of the share exchange event, the right to convert each $1,000 principal amount of notes will be changed into a right to convert such principal amount of notes into the kind and amount of shares of stock, other securities or other property or assets (including cash or any combination thereof) that a holder of a number of shares of Class A common stock equal to the conversion rate immediately prior to such share exchange event would have owned or been entitled to receive (the “reference

S-51

property”) upon such share exchange event. However, at and after the effective time of the share exchange event, (i) we or the successor or acquiring corporation, as the case may be, will continue to have the right to determine the form of consideration to be paid or delivered, as the case may be, upon conversion of notes, as set forth under “—Settlement upon conversion” and (ii)(x) any amount payable in cash upon conversion of the notes as set forth under “—Settlement upon conversion” will continue to be payable in cash, (y) any shares of our Class A common stock that we would have been required to deliver upon conversion of the notes as set forth under “—Settlement upon conversion” will instead be deliverable in the amount and type of reference property that a holder of that number of shares of our Class A common stock would have received in such share exchange event and (z) the daily VWAP will be calculated based on the value of a unit of reference property that a holder of one share of our Class A common stock would have received in such share exchange event. If the share exchange event causes our Class A common stock to be converted into, or exchanged for, the right to receive more than a single type of consideration (determined based in part upon any form of stockholder election), the reference property into which the notes will be convertible will be deemed to be the weighted average of the types and amounts of consideration actually received by the holders of our Class A common stock. If the holders of our Class A common stock receive only cash in such share exchange event, then for all conversions that occur after the effective date of such share exchange event (i) the consideration due upon conversion of each $1,000 principal amount of notes shall be solely cash in an amount equal to the conversion rate in effect on the conversion date (as may be increased as described under “—Increase in conversion rate upon conversion upon a make-whole fundamental change or during a redemption period”), multiplied by the price paid per share of Class A common stock in such share exchange event and (ii) we will satisfy our conversion obligation by paying such cash amount to converting holders on the second business day immediately following the conversion date. We will notify in writing holders, the trustee and the conversion agent (if other than the trustee) of the weighted average of the types and amounts of consideration received by the holders of our Class A common stock as soon as practicable after such determination is made.

The supplemental indenture providing that the notes will be convertible into reference property will also provide for anti-dilution and other adjustments that are as nearly equivalent as possible to the adjustments described under “—Conversion rate adjustments” above. If the reference property in respect of any such share exchange event includes shares of stock, securities or other property or assets (other than cash or cash equivalents) of a company other than us or the successor or purchasing corporation, as the case may be, in such share exchange event, such other company will also execute such supplemental indenture, and such supplemental indenture will contain such additional provisions to protect the interests of the holders, including the right of holders to require us to repurchase their notes upon a fundamental change as described under “—Fundamental change permits holders to require us to repurchase notes” below, as the board of directors reasonably considers necessary by reason of the foregoing. We will agree in the indenture not to become a party to any such share exchange event unless its terms are consistent with the foregoing.

Adjustments of prices

Whenever any provision of the indenture requires us to calculate the last reported sale prices, the daily VWAPs, the daily conversion values or the daily settlement amounts over a span of multiple days (including, without limitation, an observation period and the period, if any, for determining the “stock price” for purposes of a make-whole fundamental change), our board of directors or a committee thereof will make appropriate adjustments to each to account for any adjustment to the conversion rate that becomes effective, or any event requiring an adjustment to the conversion rate where the ex-dividend date, effective date or expiration date of the event occurs, at any time during the period when the last reported sale prices, the daily VWAPs, the daily conversion values or the daily settlement amounts are to be calculated.

S-52

Increase in conversion rate upon conversion upon a make-whole fundamental change or during a redemption period

If (i) the “effective date” (as defined below) of a “fundamental change” (as defined below and determined after giving effect to any exceptions to or exclusions from such definition, but without regard to the proviso in clause (2) of the definition thereof, a “make-whole fundamental change”) occurs prior to the maturity date of the notes, and a holder elects to convert its notes in connection with such make-whole fundamental change or (ii) we issue a notice of redemption as set forth under “—Optional redemption” and a holder elects to convert notes during the related redemption period, we will, under certain circumstances, increase the conversion rate for the notes so surrendered for conversion by a number of additional shares of Class A common stock (the “additional shares”), as described below. A conversion of notes will be deemed for these purposes to be “in connection with” such make-whole fundamental change if the relevant conversion date occurs during the period from, and including, the effective date of the make-whole fundamental change up to, and including, the close of business on the business day immediately prior to the related fundamental change repurchase date (or, in the case of a make-whole fundamental change that would have been a fundamental change but for the proviso in clause (2) of the definition thereof, the 35th trading day immediately following the effective date of such make-whole fundamental change) (such period, the “make-whole fundamental change period”).

Upon surrender of notes for conversion in connection with a make-whole fundamental change or during a redemption period, we will, at our option, satisfy our conversion obligation by physical settlement, cash settlement or combination settlement, based on the conversion rate as increased to reflect the additional shares pursuant to the table set forth below, as described under “—Settlement upon conversion.” However, if the consideration for our Class A common stock in any make-whole fundamental change described in clause (2) of the definition of fundamental change is composed entirely of cash, for any conversion of notes following the effective date of such make-whole fundamental change, the conversion obligation will be calculated based solely on the “stock price” (as defined below) for the transaction and will be deemed to be an amount of cash per $1,000 principal amount of converted notes equal to the conversion rate (including any increase to reflect the additional shares as described in this section), multiplied by such stock price. In such event, the conversion obligation will be determined and paid to holders in cash on the second business day following the conversion date. We will notify in writing holders, the trustee and the conversion agent (if other than the trustee) of the effective date of any make-whole fundamental change no later than five business days after such effective date.

The number of additional shares, if any, by which the conversion rate will be increased will be determined by reference to the table below, based on the date on which the make-whole fundamental change occurs or becomes effective (the “effective date”) or the redemption notice date, as applicable, and the price paid (or deemed to be paid) per share of our Class A common stock in the make-whole fundamental change or on the redemption notice date (the “stock price”). If the holders of our Class A common stock receive in exchange for their Class A common stock only cash in a make-whole fundamental change described in clause (2) of the definition of fundamental change, the stock price will be the cash amount paid per share. Otherwise, the stock price will be the average of the last reported sale prices of our Class A common stock over the five consecutive trading day period ending on, and including, the trading day immediately preceding the effective date of the make-whole fundamental change or the redemption notice date, as the case may be. In the event that a conversion during a redemption period would also be deemed to be in connection with a make-whole fundamental change, a holder of the notes to be converted will be entitled to a single increase to the conversion rate with respect to the first to occur of the applicable redemption notice date or the effective date of the applicable make-whole fundamental change, and the later event will be deemed not to have occurred for purposes of this section.

S-53

The stock prices set forth in the column headings of the table below will be adjusted as of any date on which the conversion rate for the notes is otherwise adjusted. The adjusted stock prices will equal the stock prices immediately prior to such adjustment, multiplied by a fraction, the numerator of which is the conversion rate immediately prior to the adjustment giving rise to the stock price adjustment and the denominator of which is the conversion rate as so adjusted. The number of additional shares as set forth in the table below will be adjusted in the same manner and at the same time as the conversion rate as set forth under “—Conversion rate adjustments.”

The following table sets forth the number of additional shares by which the conversion rate will be increased per $1,000 principal amount of notes for each stock price and effective date or redemption notice date, as applicable:

The exact stock prices and effective dates or redemption notice dates may not be set forth in the table above, in which case:

Notwithstanding the foregoing, in no event will the conversion rate per $1,000 principal amount of notes exceed              shares of Class A common stock, subject to adjustment in the same manner as the conversion rate as set forth under “—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.

Fundamental change permits holders to require us to repurchase notes

If a “fundamental change” (as defined below in this section) occurs at any time prior to the maturity date, holders will have the right, at their option, to require us to repurchase for cash all of their notes, or any portion

S-54

of the principal amount thereof that is equal to $1,000 or an integral multiple of $1,000. The fundamental change repurchase date will be a date specified by us that is not less than 20 or more than 35 business days following the date of our fundamental change notice as described below. The fundamental change repurchase date shall be subject to postponement in order to allow us to comply with applicable law as a result of changes to such applicable law occurring after the date of the indenture.

The fundamental change repurchase price we are required to pay will be 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 (unless the fundamental change repurchase date falls after a regular record date but on or prior to the interest payment date to which such regular record date relates, in which case we will instead pay the full amount of accrued and unpaid interest to the holder of record on such regular record date, and the fundamental change repurchase price will be equal to 100% of the principal amount of the notes to be repurchased).

A “fundamental change” will be deemed to have occurred at the time after the notes are originally issued if any of the following occurs:

S-55

A transaction or transactions described in clauses (1) or (2) above will not constitute a fundamental change, however, if at least 90% of the consideration received or to be received by our Class A common stockholders, excluding cash payments for fractional shares and cash payments made in respect of dissenters’ statutory appraisal rights, in connection with such transaction or transactions consists of shares of common stock that are listed or quoted on any of The New York Stock Exchange, The Nasdaq Global Select Market or The Nasdaq Global Market (or any of their respective successors) or will be so listed or quoted when issued or exchanged in connection with such transaction or transactions and as a result of such transaction or transactions such consideration, excluding cash payments for fractional shares and cash payments made in respect of dissenters’ statutory appraisal rights (subject to the provisions set forth above under “—Conversion rights—Settlement upon conversion”) becomes reference property for the notes.

If any transaction in which our Class A common stock is replaced by the securities of another entity occurs, following completion of any related make-whole fundamental change period (or, in the case of a transaction that would have been a fundamental change or a make-whole fundamental change but for the immediately preceding paragraph, following the effective date of such transaction), references to us in the definition of “fundamental change” above shall instead be references to such other entity.

“Permitted Holders” means (a) James R. Scapa, our Co-Founder and our Chairman and Chief Executive Officer as of the date of the indenture, and (b) George J. Christ, our Co-Founder.

For purposes of the definition of “fundamental change” above, any transaction that constitutes a fundamental change pursuant to both clause (1) and clause (2) of such definition (without giving effect to the proviso to clause (2)) shall be deemed a fundamental change solely under clause (2) of such definition (subject to the proviso to clause (2)).

On or before the 20th day after the occurrence of a fundamental change, we will provide to all holders of the notes and the trustee and paying agent a written notice of the occurrence of the fundamental change and of the resulting repurchase right. Such notice shall state, among other things:

S-56

Simultaneously with providing such notice, we will publish the information on our website, through a press release, or through such other public medium as we may use at that time.

To exercise the fundamental change repurchase right, you must deliver, on or before the close of business on the business day immediately preceding the fundamental change repurchase date, the notes to be repurchased, duly endorsed for transfer, together with a written repurchase notice, to the paying agent. Each repurchase notice must state:

If the notes are not in certificated form, such repurchase notice must comply with appropriate DTC procedures.

Holders may withdraw any repurchase notice (in whole or in part) by a written notice of withdrawal delivered to the paying agent prior to the close of business on the business day immediately preceding the fundamental change repurchase date. The notice of withdrawal shall state:

If the notes are not in certificated form, such notice of withdrawal must comply with appropriate DTC procedures.

We will be required to repurchase the notes on the fundamental change repurchase date. Holders who have exercised the repurchase right will receive payment of the fundamental change repurchase price on the later of (i) the fundamental change repurchase date and (ii) the time of book-entry transfer or the delivery of the notes. If the paying agent holds money sufficient to pay the fundamental change repurchase price of the notes on the fundamental change repurchase date, then, with respect to the notes that have been properly surrendered for repurchase and have not been validly withdrawn:

In connection with any repurchase offer pursuant to a fundamental change repurchase notice, we will, if required by applicable law:

S-57

in each case, so as to permit the rights and obligations under this “—Fundamental change permits holders to require us to repurchase notes” to be exercised in the time and in the manner specified in the indenture.

To the extent that, as a result of a change in laws or regulations occurring after the first date on which the notes are issued, the provisions of any securities laws conflict with the provisions of the indenture relating to our obligations to purchase the notes upon a fundamental change, we will comply with applicable securities laws and regulations and will not be deemed to have breached our obligations under such provisions of the indenture by virtue of such conflict.

No notes may be repurchased on any date at the option of holders upon a fundamental change if the principal amount of the notes has been accelerated, and such acceleration has not been rescinded, on or prior to such date (except in the case of an acceleration resulting from a default by us in the payment of the fundamental change repurchase price with respect to such notes).

Notwithstanding anything to the contrary herein, we will not be required to repurchase, or to make an offer to repurchase, the notes upon a fundamental change if a third party makes such an offer in the same manner, at the same time and otherwise in compliance with the requirements for an offer made by us as set forth in the indenture, and such third party purchases all notes properly surrendered and not validly withdrawn under its offer in the same manner, at the same time and otherwise in compliance with the requirements for an offer made by us as set forth in the indenture.

The repurchase rights of the holders could discourage a potential acquirer of us. The fundamental change repurchase feature, however, is not the result of management’s knowledge of any specific effort to obtain control of us by any means or part of a plan by management to adopt a series of anti-takeover provisions.

The term fundamental change is limited to specified transactions and may not include other events that might adversely affect our financial condition. In addition, the requirement that we offer to repurchase the notes upon a fundamental change may not protect holders in the event of a highly leveraged transaction, reorganization, merger or similar transaction involving us.

Furthermore, holders may not be entitled to require us to repurchase their notes or be entitled to an increase in the conversion rate upon conversion as described under “—Increase in conversion rate upon conversion upon a make-whole fundamental change or during a redemption period” in circumstances involving a significant change in the composition of our board unless such change is in connection with a fundamental change or make-whole fundamental change as described herein.

The definition of fundamental change includes a phrase relating to the sale, lease or other transfer of “all or substantially all” of our consolidated assets. There is no precise, established definition of the phrase “substantially all” under applicable law. Accordingly, the ability of a holder of the notes to require us to repurchase its notes as a result of the sale, lease or other transfer of less than all of our assets may be uncertain.

If a fundamental change were to occur, we may not have enough funds to pay the fundamental change repurchase price. Our ability to repurchase the notes for cash may also be limited by restrictions on our ability to obtain funds for such repurchase through dividends from our subsidiaries, the terms of our then existing borrowing arrangements or otherwise. See “Risk factors—Risks related to the notes—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