Summary Prospectus by Investment Company - Form 497K

May 1, 2024

Summary Prospectus

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

(NYSE Arca - CPSM)

Before you invest, you may want to review the Fund's prospectus and statement of additional information, which contain more information about the Fund and its risks. You can find the Fund's prospectus, statement of additional information, reports to shareholders and other information about the Fund online at www.calamos.com/resources. You can also get this information at no cost by calling 866.363.9219 or by sending an e-mail request to [email protected]. The current prospectus and statement of additional information, both dated May 1, 2024 (and as each may be amended or supplemented), are incorporated by reference into this summary prospectus.

Investment Objective

Calamos S&P 500 Structured Alt Protection ETF - May (the "Fund") seeks to provide investment results that, before taking fees and expenses into account, match the positive price return of the SPDR^®​ S&P 500^®​ ETF Trust ("Underlying ETF") up to a cap of 9.81% (the "Cap"), while protecting against 100% of negative price return of the Underlying ETF (before fees and expenses), for the period from May 1, 2024 through April 30, 2025.

Fees and Expenses of the Fund

The following table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund ("Fund Shares"). Investors may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.

Annual Fund Operating Expenses (ongoing expenses that you pay each year as a percentage of the value of your investments):

1 "Other Expenses" is an estimate based on the expenses the Fund expects to incur for the current fiscal year.

Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated, and then sell all of your Fund Shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs, whether you sell or hold your Fund Shares, would be:

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund Shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the example, affect the Fund's performance. Because the Fund has not yet commenced operations, portfolio turnover information is unavailable at this time.

Principal Investment Strategies

The Fund is an actively managed exchange-traded fund ("ETF") that is designed to provide investors with the opportunity to benefit from increases in the Underlying ETF's share price up to the stated cap over a specified period of time of approximately one-year (the "Outcome Period"), while providing protection against decreases in the Underlying ETF's share price over the same Outcome Period (before taking fees and expenses into account).

Under normal market conditions, the Fund will invest substantially all of its assets in FLexible EXchange Options ("FLEX Options") that reference the price performance of the SPDR^®​ S&P 500^®​ ETF Trust (the "Underlying ETF"). FLEX Options are customized equity or index option contracts that trade on an exchange but provide investors with the ability to customize key contract terms like exercise prices, styles and expiration dates.

The Underlying ETF is an exchange-traded unit investment trust that uses a replication strategy, meaning it invests in as many of the stocks in the S&P 500^®​ Index as is practicable. PDR Services, LLC ("PDR") serves as the Underlying ETF's sponsor. The investment objective of the

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

Underlying ETF is to seek to provide investment results that, before fees and expenses, correspond generally to the price and yield performance of the S&P 500^®​ Index. The Fund's performance will not reflect the payment of dividends by the Underlying ETF. See "The Underlying ETF" for more information.

The returns an investor will receive from an investment in the Fund have characteristics that are distinct from many other investment vehicles, including the Underlying ETF. It is important that you understand these characteristics before making an investment in the Fund.

The Fund uses FLEX Options to employ a capital protected target outcome strategy. Target outcome strategies seek to produce pre-determined investment outcomes based upon the performance of an underlying security or index. The pre-determined outcomes sought by the Fund, which include capital protection to absorb 100% of losses (before fees and expenses) in the Underlying ETF (the "Capital Protection") and upside participation to a stated cap (before fees and expenses) (the "Cap"), are based on the price performance of the Underlying ETF over an Outcome Period.

The outcomes the Fund seeks for investors that hold Fund Shares for an entire Outcome Period are as follows, though there can be no guarantee these results will be achieved:

• If the Underlying ETF appreciates over the Outcome Period, the combination of FLEX Options held by the Fund seeks to provide upside participation matching that of the Underlying ETF, up to a cap that is determined at the start of the Outcome Period.

• If the Underlying ETF decreases over the Outcome Period, the combination of FLEX Options held by the Fund seeks to provide protection against 100% of Underlying ETF losses, prior to taking into account the Fund's fees and expenses.

The Fund does not seek to provide capital protection against 100% of losses (before fees and expenses) of the Underlying ETF as of any time other than the end of the Outcome Period.

For the Outcome Period beginning on May 1, 2024 through April 30, 2025, the Cap is 9.81% and the Capital Protection is 100%. When the Fund's fees and expenses are taken into account, the Cap is 9.12% and the Capital Protection is 99.31%. The Cap and Capital Protection will be further reduced by any brokerage commissions, trading fees, taxes and extraordinary expenses not included in the Fund's management fee.

Subsequent Outcome Periods will begin on the day the prior Outcome Period ends and will end on the approximate one-year anniversary of that new Outcome Period. On the first day of each new Outcome Period, the Fund resets by investing in a new set of FLEX Options that are designed to provide a new cap for the new Outcome Period. This means that the Cap will change for each Outcome Period based upon prevailing market conditions at the beginning of each Outcome Period. The capital protection will remain the same for each Outcome Period. The Capital Protection and Cap, and the Fund's value relative to each, should be considered before investing in the Fund. The Fund will be perpetually offered and not terminate after the current or any subsequent Outcome Period. Approximately one week prior to the end of an Outcome Period, the Fund's website will be updated to alert existing shareholders that the Outcome Period is approaching its conclusion and will disclose the anticipated Cap range for the next Outcome Period. See "Subsequent Outcome Periods" for more information.

Upon conclusion of the Outcome Period, the Fund will receive the cash value of all the FLEX Options it held for that Outcome Period. It will then invest in a new series of FLEX Options with an expiration date of approximately one year in the future, and a new Outcome Period will begin. Each FLEX Option's value is ultimately derived from the performance of the Underlying ETF's share price during that time. As the terms of the FLEX Options do not change during an Outcome Period, the outcomes, including the Cap and Capital Protection discussed below, will be measured to the Fund's net asset value ("NAV") on the first day of the Outcome Period.

The stated Cap and Capital Protection may only be realized by investors who continuously hold Fund Shares from the commencement of an Outcome Period until its conclusion. An investor who purchases Fund Shares other than on the first day of an Outcome Period and/or sells Fund Shares prior to the end of an Outcome Period may experience results that are very different from the target outcomes sought by the Fund for that Outcome Period. While the Cap and Capital Protection provide the intended outcomes only for investors that hold their Fund Shares throughout the complete term of the Outcome Period, an investor can expect the value of their Fund Shares to generally move in the same direction as the Underlying ETF during the Outcome Period. If investors buy or sell on a date other than the start or end date of the Outcome Period, their returns will be different and they may incur losses in excess of the Capital Protection level (i.e., losses exceeding 0%) and they may not experience gains up to the Cap. See "Capital Protection and Cap" for more information.

The Fund's website, www.calamos.com, provides information relating to the possible outcomes for an investor of an investment in the Fund on a daily basis, if purchased on that date and held through the end of the Outcome Period, including the Fund's value relative to the Cap and Capital Protection. Before purchasing Fund Shares, an investor should visit the Fund's website to review this information and understand the possible outcomes of an investment in Fund Shares on a particular day and held through the end of the Outcome Period.

The Fund's investment objective is not a fundamental policy, and therefore may be changed by the Board without shareholder approval.

The Fund seeks to generate returns that match the Underlying ETF, up to the Cap (discussed in detail below), while limiting downside losses. The hypothetical illustrations provided below are designed to illustrate the outcomes that the Fund seeks to provide for investors who hold Fund Shares for the entirety of the Outcome Period. The hypothetical examples set forth below do not represent the performance of the

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

Fund and investors should not rely on the hypothetical examples shown below as an indication of the actual or future performance of the Fund. There is no guarantee that the Fund will be successful in its attempt to provide the target outcomes for an Outcome Period. The returns that the Fund seeks to provide do not include the costs associated with purchasing Fund Shares and certain expenses incurred by the Fund. In the payoff profile illustration, the dotted line represents the Underlying ETF's performance, and the solid line represents the return profile gross of fees and expenses sought by the Fund in relation to the Underlying ETF's indicated performance. The bar chart below represents the Fund's hypothetical intended return profile based upon the performance of the Underlying ETF.

Explanation of diagram:

1. Calamos S&P 500 Structured Alt Protection ETF - May Participation Layer: The dotted grey line represents the first layer, which involves purchasing a near zero-strike (i.e., deep in-the-money) call on the reference asset, at a pre-determined strike to provide full participation to the price return of the underlying reference asset. In other words, the full price participation provided by this layer provides potential gains and losses that are tantamount to that of owning the underlying reference asset outright, except that this layer does not participate in the dividend yield of the underlying reference asset.

2. Capital Protection Layer: The solid grey line represents the second layer, which involves purchasing an at-the-money put option, which produces protection equal to 100% of losses (before fees and expenses) of the price return of the reference asset, over the Outcome Period.

3. Upside Participation Layer (the "Cap"): The solid black line illustrates the final layer, which involves selling an out-of-the-money call, thereby creating the upside cap. The strike price at which the call is sold is determined so that the combined net options purchase price is approximately equal to the underlying asset's current value. The cost of this layer is a credit equal to the price that would make the total package "no-cost" or fully financed.

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

The Fund is classified as "non-diversified" under the Investment Company Act of 1940, as amended (the "1940 Act").

Capital Protection and Cap

The Fund seeks to provide capital protection to absorb 100% of losses (before fees and expenses) of the Underlying ETF at the end of each Outcome Period. When the Fund's management fees are taken into account, the Capital Protection level is reduced to 99.31%. The Capital Protection level will be further reduced by any brokerage commissions, trading fees, taxes and extraordinary expenses not included in the Fund's management fee. If the Fund is required to increase its holdings of cash during the Outcome Period to pay fees and expenses incurred by the Fund, the Capital Protection level may be further reduced. The Fund does not seek to provide capital protection against 100% of losses (before fees and expenses) of the Underlying ETF as of any time other than the end of the Outcome Period.

During the Outcome Period, there may be periods of significant disparity between the Fund's NAV and the Underlying ETF's price performance. As the Underlying ETF price and the Fund's NAV change over the Outcome Period, an investor acquiring Fund Shares after the start of the Outcome Period will likely have a different return potential than an investor who purchased Fund Shares at the start of the Outcome Period. This is because while the Cap and Capital Protection for the Outcome Period are fixed levels that are calculated in relation to the Underlying ETF price and the Fund's NAV at the start of an Outcome Period and remain constant throughout the Outcome Period, an investor purchasing Fund Shares at market value during the Outcome Period likely purchased Fund Shares at a price that is different from the Fund's NAV at the start of the Outcome Period (i.e., the NAV that the Cap and Capital Protection reference). For example, if an investor purchases Fund Shares during an Outcome Period at a time when the Fund has increased in value from the value of the Fund on the first day of the Outcome Period (the "Initial Fund Value"), that investor's Cap will essentially be decreased by the amount of the increase in the Underlying ETF's value, and the capital protection will not set in until the Fund's NAV returns to its Initial Fund Value (i.e., a shareholder must experience losses prior to gaining the protection offered by the Fund's Capital Protection because the Fund must first decrease in value to its Initial Fund Value for the Outcome Period before subsequent losses will be protected by the Capital Protection). Conversely, if an investor purchases Fund Shares during an Outcome Period at a time when the Underlying ETF has decreased in value, the Fund's NAV may dip below the Initial Fund Value. However, in this scenario, that investor's potential gain could be larger than the Fund's Cap for the Outcome Period because the investor may experience the full gain if the Fund recovers the value it has lost from the first day of the Outcome Period through the date the investor purchased its Fund Shares plus any additional gains between the Initial Fund Value and the Cap. There is no guarantee that the Fund will recover such value or experience such gains. The Cap and capital protection relative to the Initial Fund Value, however, will not change over the Outcome Period.

While the Fund seeks to provide 100% protection against losses experienced by the Underlying ETF (before fees and expenses) for shareholders who hold Fund Shares for an entire Outcome Period, there is no guarantee it will successfully do so. If the Fund's NAV has increased significantly, a shareholder that purchases Fund Shares after the first day of an Outcome Period could lose their entire investment. An investment in the Fund is only appropriate for shareholders willing to bear those losses. There is no guarantee the capital protection and cap will be successful and a shareholder investing at the beginning of an Outcome Period could also lose their entire investment.

The returns of the Fund are subject to a cap for each Outcome Period, calculated (before fees and expenses) at the beginning of each Outcome Period.. Unlike other investment products, the potential returns an investor can receive from the Fund are subject to a pre-determined upside return Cap that represents the maximum percentage return an investor can achieve from an investment in the Fund for an entire Outcome Period. If the Underlying ETF experiences any percentage gains over the amount of the Cap, Fund shareholders will not experience those

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

gains. Therefore, regardless of the price return of the Underlying ETF, the Cap (net of fees) is the maximum return an investor can achieve from an investment in the Fund for that Outcome Period. The Cap is set on the first day of each Outcome Period. The Cap is provided prior to taking into account annual Fund management fees of 0.69% of the Fund's daily net assets, brokerage commissions, trading fees, taxes and any extraordinary expenses (such as unexpected litigation) incurred by the Fund. The pre-determined Cap applicable to an Outcome Period will vary based on prevailing market conditions at the time that the Cap is set, including interest rate levels, Underlying ETF volatility, and the relationship of puts and calls on the FLEX Options.

The Cap level is a result of the design of the Fund's principal investment strategy. To provide the Capital Protected Target Outcome, the Fund purchases and sells a series of put and call FLEX Options on or around the last business day of the month prior to the beginning of an Outcome Period. As the purchaser of these FLEX Options, the Fund is obligated to pay a premium to the seller of those FLEX Options. The Adviser will calculate the amount of premiums that the Fund will owe on the put options acquired to provide the Capital Protection and will then sell call FLEX Options with terms that entitle the Fund to receive premiums such that the net amount of premiums paid per unit of the Underlying ETF is approximately equal to the price per unit of shares of the Underlying ETF. The Cap is the strike price of those FLEX Options the Fund is selling. The Cap, and the Fund's value relative to it on any given day, should be considered before investing in the Fund. If an investor purchases Fund Shares during an Outcome Period, and the Fund has already increased in value above its Initial Fund Value for that Outcome Period to a level near the Cap, an investor purchasing Fund Shares will have limited to no gain potential for the remainder of the Outcome Period (because the investor's potential gain will be limited to the difference between the Fund's NAV on the date the investor purchased the Fund Shares and the Cap). However, the investor will remain vulnerable to significant downside risk because the investor will bear the losses between the price at which it purchased its Fund Shares and the Initial Fund Value for the Outcome Period before subsequent losses will be protected by the Capital Protection. If an investor buys Fund Shares when the price exceeds the Cap, an investor selling their shares at the end of the Outcome Period will not experience any gain regardless of the price return of the Underlying ETF.

There is no guarantee that the Fund will be successful in providing these investment outcomes for any Outcome Period, and an investor may experience returns on the Fund significantly below the Cap.

In periods of extreme market volatility or during market disruption events, the Fund's ability to offset investor losses through the use of the FLEX Options to achieve the stated Capital Protection, or provide a return up to the stated upside Cap may be impaired, resulting in an upside limit significantly below the Cap and downside protection significantly lower than full capital protection (i.e., losses greater than 0%), because the Fund may not be able to trade or exercise existing FLEX Options, or may not receive timely payment from its counterparties. An investor may lose their entire investment and an investment in the Fund is only appropriate for investors willing to bear those losses.

For each Outcome Period, the Fund will invest in both purchased and written put and call FLEX Options that reference the Underlying ETF. Because the value of the Fund is based on FLEX Options that reference the Underlying ETF and not the Underlying ETF directly, variations in the value of the FLEX Options impact the correlation between the Fund's NAV and the price of the Underlying ETF.

General Information about FLEX Options

FLEX Options are customizable exchange-traded option contracts guaranteed for settlement by the Options Clearing Corporation ("OCC"). The OCC guarantees performance by each of the counterparties to the FLEX Options, becoming the "buyer for every seller and the seller for every buyer," with the goal of protecting clearing members and options traders from counterparty risk. The OCC may make adjustments to FLEX Options for certain significant events, as more fully described in the Fund's Statement of Additional Information. Although guaranteed for settlement by the OCC, FLEX Options are still subject to counterparty risk with the OCC and subject to the risk that the OCC may fail to perform the settlement of the FLEX Options due to bankruptcy or other adverse reasons. The FLEX Options that the Fund will hold that reference the Underlying ETF will give the Fund the right or the obligation to either receive or deliver shares of the Underlying ETF, or the right or the obligation to either receive or deliver a cash payment on the option expiration date based upon the difference between the Underlying ETF's value and a strike price, depending on whether the option is a put or call option and whether the Fund purchases or sells the option. The FLEX Options held by the Fund are European style options, which are exercisable at the strike price only on the FLEX Option expiration date. The Fund will generally, under normal conditions, hold FLEX Options for each Outcome Period. The Fund will purchase call options (giving the Fund the right to receive shares of the Underlying ETF or a cash payment) and put options (giving the Fund the right to deliver shares of the Underlying ETF or a cash payment), while simultaneously selling (i.e., writing) call options (giving the Fund the obligation to deliver shares of the Underlying ETF or a cash payment). The Fund intends to structure the FLEX Options so that any amount owed by the Fund on the written FLEX Options will be covered by payouts at expiration from the purchased FLEX Options. As a result, the Fund expects the FLEX Options to be fully covered and no additional collateral will be necessary during the life of the Fund. The Fund receives premiums in exchange for the written FLEX Options and pays premiums in exchange for the purchased FLEX Options. The OCC and securities exchanges on which the FLEX Options are listed do not charge ongoing fees to writers or purchasers of the FLEX Options during their life for continuing to hold the option contracts but may charge transaction fees. Each of the FLEX Options purchased and sold throughout the Outcome Period will have the same terms, such as strike price and expiration date, as the FLEX Options purchased and sold on the first day of the Outcome Period. On the Flex Options expiration date, the Fund intends to sell the Flex Options prior to their expiration or cash-settle the Flex Options and use the resulting proceeds to purchase new Flex Options for the next Outcome Period.

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

The Underlying ETF

The Underlying ETF is an exchange-traded unit investment trust that uses a replication strategy, meaning it invests in as many of the stocks in the S&P 500^®​ Index as is practicable. PDR Services, LLC ("PDR") serves as the Underlying ETF's sponsor. The investment objective of the Underlying ETF is to seek to provide investment results that, before fees and expenses, correspond generally to the price and yield performance of the S&P 500^®​ Index (the "Index"). See below for a description of the Underlying ETF's principal investment strategies and risks. You can find the Underlying ETF's prospectus and other information about the ETF, including the statement of additional information and most recent reports to shareholders, online at https://us.spdrs.com/en/etf/spdr-sp-500-etf-SPY.

The summary information below regarding the Underlying ETF comes from its filings with the SEC. You are urged to refer to the SEC filings made by the Underlying ETF and to other publicly available information (e.g., the ETF's annual reports) to obtain an understanding of the ETF's business and financial prospects. The following description of the Underlying ETF's principal investment strategies was taken directly from the Underlying ETF's prospectus, dated January 26, 2024 ("SPY" refers to the Underlying ETF; other defined terms have been modified).

"SPY seeks to achieve its investment objective by holding a portfolio of the common stocks that are included in the Index (the "Portfolio"), with the weight of each stock in SPY's Portfolio substantially corresponding to the weight of such stock in the Index. In SPY's prospectus, the term "Portfolio Securities" refers to the common stocks that are actually held by SPY and make up SPY's Portfolio, while the term "Index Securities" refers to the common stocks that are included in the Index, as determined by the index provider, S&P Dow Jones Indices LLC ("S&P"). At any time, SPY's Portfolio will consist of as many of the Index Securities as is practicable. To maintain the correspondence between the composition and weightings of Portfolio Securities and Index Securities, State Street Global Advisors Trust Company (the "Trustee") or its parent company, State Street Bank and Trust Company ("SSBT") adjusts SPY's Portfolio from time to time to conform to periodic changes made by S&P to the identity and/or relative weightings of Index Securities in the Index. SPY's Trustee or SSBT aggregates certain of these adjustments and makes changes to SPY's Portfolio at least monthly, or more frequently in the case of significant changes to the Index. SPY may pay transaction costs, such as brokerage commissions, when it buys and sells securities (or "turns over" its Portfolio). Such transaction costs may be higher if there are significant rebalancings of Index Securities in the Index, which may also result in higher taxes when SPY's units are held in a taxable account. These costs, which are not reflected in SPY's estimated annual Trust ordinary operating expenses, affect SPY's performance. During the most recent fiscal year, SPY's portfolio turnover rate was 2% of the average value of its portfolio. SPY's portfolio turnover rate does not include securities received or delivered from processing creations or redemptions of SPY's units. Portfolio turnover will be a function of changes to the Index as well as requirements of SPY's trust agreement. ... Although SPY may fail to own certain Index Securities at any particular time, SPY generally will be substantially invested in Index Securities, which should result in a close correspondence between the performance of the Index and the performance of SPY. ... SPY does not hold or trade futures or swaps and is not a commodity pool... . The Index includes five hundred (500) selected companies, all of which are listed on national stock exchanges and spans a broad range of major industries. ... Since 1968, the Index has been a component of the U.S. Commerce Department's list of Leading Indicators that track key sectors of the U.S. economy. Current information regarding the market value of the Index is available from market information services. The Index is determined, comprised and calculated without regard to SPY."

As of December 1, 2023, the Underlying ETF had significant investments in information technology companies.

Subsequent Outcome Periods

The Fund will alert existing shareholders to the new Cap at the beginning of each new Outcome Period in the following manner:

1. Approximately one week prior to the end of the current Outcome Period, the Fund will make a sticker filing that will alert existing shareholders that the Outcome Period is approaching its conclusion and disclose the anticipated Cap range for the next Outcome Period. This filing will be mailed to existing shareholders.

2. Following the close of business on the last day of the Outcome Period, the Fund will make a sticker filing that discloses the Fund's Cap for the next Outcome Period. This filing will be mailed to existing shareholders.

3. On the first day of the new Outcome Period, the Fund will file a full prospectus that incorporates the sticker filing from the previous evening which replaces the Caps/dates associated with the previous Outcome Period with the Caps/dates associated with the new Outcome Period. Correspondingly, the Fund will file a revised summary prospectus that reflects such changes.

The information referenced above will also be available on the Fund's website at www.calamos.com.

Principal Risks

An investment in the Fund is subject to risks, and you could lose money on your investment in the Fund. There can be no assurance that the Fund will achieve its investment objective. You should not consider investing in the Fund if your investment objective differs from the Fund's investment objective or if you are not willing to accept the principal risks associated with an investment in the Fund. The risks associated with an investment in the Fund can increase during times of significant market volatility. Your investment in the Fund is not a deposit in a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The principal risks are presented in alphabetical order to facilitate finding particular risks and comparing them with other funds. Each risk summarized below is

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

considered a "principal risk" of investing in the Fund, regardless of the order in which it appears. The principal risks of investing in the Fund include:

• Authorized Participant Concentration Risk - Only an Authorized Participant may engage in creation or redemption transactions directly with the Fund, and none of those Authorized Participants is obligated to engage in creation and/or redemption transactions. The Fund has a limited number of institutions that may act as Authorized Participants on an agency basis (i.e., on behalf of other market participants). To the extent that Authorized Participants exit the business or are unable to proceed with creation or redemption orders with respect to the Fund and no other Authorized Participant is able to step forward to create or redeem, Fund Shares may be more likely to trade at a premium or discount to NAV and possibly face trading halts or delisting. Authorized Participant concentration risk may be heightened for ETFs, such as the Fund, that invest in securities issued by non-U.S. issuers or other securities or instruments that have lower trading volumes.

• Cap Change Risk - A new Cap is established at the beginning of each Outcome Period and is dependent on prevailing market conditions at the time the Cap is established. As such, the Cap may rise or fall from one Outcome Period to the next and is unlikely to remain the same for consecutive Outcome Periods. Investors should monitor the changes in the Cap for each Outcome Period, information for which will be made available pursuant to the procedure outlined in the Fund's prospectus.

• Capital Protection Risk - There can be no guarantee that the Fund will be successful in its strategy to provide protection against 100% of Underlying ETF losses if the Underlying ETF's share price decreases over the duration of the Outcome Period. The Fund's strategy seeks to deliver returns that match those of the Underlying ETF (up to the Cap), while limiting downside losses, if Fund Shares are held at the time at which the Fund enters into the FLEX Options and held until those FLEX Options expire at the end of the Outcome Period. In the event an investor purchases Fund Shares after the FLEX Options were entered into or sells Fund Shares prior to the expiration of the FLEX Options, the Capital Protection that the Fund seeks to provide may not be available. If the Outcome Period has begun and the Underlying ETF has increased in value, the Capital Protection will not protect any decreases in the value of the Underlying ETF to the extent of such appreciation, and therefore an investor may experience losses from this appreciated value until the Fund reaches its original NAV from the commencement of the Outcome Period. Similarly, if an investor purchases Fund Shares after the commencement of the Outcome period and the Underlying ETF has increased in value, an investor purchasing Shares at that point will not benefit from the Capital Protection until the Underlying ETF's value decreases to its original value at the commencement of the Outcome Period. Accordingly, such investor will not receive the protection that the Fund seeks to provide until the Fund experiences losses that return it to its value at the commencement of the Outcome Period. If the FLEX Options (and therefore the Capital Protection) do not perform as expected, an investor may experience significant losses on its investment, including the loss of its entire investment.

• Capped Upside Risk - The Fund's strategy seeks to provide returns that are subject to the Cap. In the event that the Underlying ETF experiences gains in excess of the Cap for the Outcome Period, the Fund will not participate in, and will underperform the Underlying ETF to the extent of, those gains beyond the Cap. The Fund's strategy seeks to deliver returns that match those of the Underlying ETF (up to the Cap), while protecting against the entirety of downside losses of the Underlying ETF, if Fund Shares are held at the time at which the Fund enters into the FLEX Options and held until those FLEX Options expire at the end of the Outcome Period. In the event an investor purchases Fund Shares after the FLEX Options were entered into, there may be little or no ability for that investor to experience an investment gain on their Fund Shares (and such investor may be subjected to potential losses between that Fund Share price and the Fund's NAV at the commencement of the Outcome Period). Further, because the FLEX Options are designed to produce returns that match the price return of the Underlying ETF (subject to the Cap) on the last day of the Outcome Period, if an investor sells Fund Shares prior to the expiration date of the FLEX Options such investor may sell at a point where the Fund's performance does not match the performance of the Underlying ETF over the Outcome Period, and therefore may sell at a point where the Fund has underperformed the Underlying ETF.

• Cash Holdings Risk - To the extent the Fund holds cash positions, the Fund risks achieving lower returns and potential lost opportunities to participate in market appreciation which could negatively impact the Fund's performance and ability to achieve its investment objective.

• Clearing Member Default Risk - Transactions in some types of derivatives, including FLEX Options, are required to be centrally cleared ("cleared derivatives"). In a transaction involving cleared derivatives, the Fund's counterparty is a clearing house, such as the OCC, rather than a bank or broker. Since the Fund is not a member of clearing houses and only members of a clearing house ("clearing members") can participate directly in the clearing house, the Fund will hold cleared derivatives through accounts at clearing members. In cleared derivatives positions, the Fund will make payments (including margin payments) to, and receive payments from, a clearing house through their accounts at clearing members. Customer funds held at a clearing organization in connection with any option contracts are held in a commingled omnibus account and are not identified to the name of the clearing member's individual customers. As a result, assets deposited by the Fund with any clearing member as margin for its FLEX Options may, in certain circumstances, be used to satisfy losses of other clients of the Fund's clearing member. In addition, although clearing members guarantee performance of their clients' obligations to the clearing house, there is a risk that the assets of the Fund might not be fully protected in the event of the clearing member's bankruptcy. The Fund is also subject to the risk that a limited number of clearing members are willing to transact on the Fund's behalf, which heightens the risks associated with a clearing member's default. If a clearing member defaults the Fund could lose some or all of the benefits of a transaction entered into by the Fund with the clearing member. The loss of a clearing member for the Fund to transact with could result in increased transaction costs and other operational issues that could impede the Fund's ability to implement its investment strategy. If the Fund cannot find a clearing member to transact with on the Fund's behalf, the Fund may be unable to effectively implement its investment strategy.

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

• Correlation Risk - The FLEX Options held by the Fund will be exercisable at the strike price only on their expiration date. Prior to the expiration date, the value of the FLEX Options will be determined based upon market quotations or using other recognized pricing methods, consistent with the Fund's valuation policy. Because a component of the FLEX option's value will be affected by, among other things, changes in the Underlying ETF's share price, changes in interest rates, changes in the actual and implied volatility of the Underlying ETF's share price and the remaining time until the FLEX Options expire, the value of the Fund's FLEX Options positions is not anticipated to increase or decrease at the same rate as the Underlying ETF's share price, and it is possible they may move in different directions, and as a result, the Fund's NAV may not increase or decrease at the same rate as the Underlying ETF's share price. The Fund's strategy is designed to produce the outcomes upon the expiration of the FLEX Options on the last business day of the Outcome Period, and it should not be expected that the outcomes will be provided at any point other than the end of the Outcome Period.

• Costs of Buying and Selling Fund Shares - Due to the costs of buying or selling Fund Shares, including brokerage commissions imposed by brokers and bid/ask spreads, frequent trading of Fund Shares may significantly reduce investment results and an investment in Fund Shares may not be advisable for investors who anticipate regularly making small investments.

• Derivatives Risk - Derivatives are instruments, such as options, futures and forward foreign currency contracts, whose value is derived from that of other assets, rates or indices. The use of derivatives for non-hedging purposes may be considered more speculative than other types of investments. Derivatives can be used for hedging (attempting to reduce risk by offsetting one investment position with another) or non-hedging purposes. Hedging with derivatives may increase expenses, and there is no guarantee that a hedging strategy will work. While hedging can reduce or eliminate losses, it can also reduce or eliminate gains. In addition, derivative instruments are subject to counterparty risk, meaning that the party with whom the Fund enters into a derivative transaction may experience a significant credit event and/or may be unwilling or unable to make timely settlement payments or otherwise honor its obligations. Changes in the value of a derivative may not correlate perfectly with the underlying asset, rate or index, and the Fund could lose more than the principal amount invested.

• Equity Securities Risk - The securities markets are volatile, and the market prices of the Underlying ETF's securities may decline generally. The price of equity securities fluctuates based on changes in a company's financial condition and overall market and economic conditions. If the market prices of the securities owned by the Underlying ETF fall, the value of your investment in the Fund will decline.

• FLEX Options Risk - The Fund may invest in FLEX Options issued and guaranteed for settlement by The Options Clearing Corporation ("OCC"). FLEX Options are customized option contracts that trade on an exchange but provide investors with the ability to customize key contract terms like strike price, style and expiration date while achieving price discovery in competitive, transparent auctions markets and avoiding the counterparty exposure of over-the-counter options positions. Like traditional exchange-traded options, FLEX Options are guaranteed for settlement by the OCC, a market clearinghouse that guarantees performance by counterparties to certain derivatives contracts. The Fund bears the risk that the OCC will be unable or unwilling to perform its obligations under the FLEX Options contracts. Additionally, FLEX Options may be illiquid, and in such cases, the Fund may have difficulty closing out certain FLEX Options positions at desired times and prices. The FLEX Options held by the Fund will be exercisable at the strike price only on their expiration date. Prior to the expiration date, the value of the FLEX Options will be determined based upon market quotations or using other recognized pricing methods. The value of the FLEX Options prior to the expiration date may vary because of related factors other than the value of the reference asset. Factors that may influence the value of the FLEX Options, other than gains or losses in the reference asset, may include interest rate changes, changing supply and demand, decreased liquidity of the FLEX Options and changing volatility levels of the reference asset. In connection with the creation and redemption of Fund Shares, to the extent market participants are not willing or able to enter into FLEX Option transactions with the Fund at prices that reflect the market price of the Fund Shares, the Fund's NAV and, in tum the share price of the Fund, could be negatively impacted. The Fund may experience substantial downside from specific FLEX Option positions and certain FLEX Option positions may expire worthless.

• Investment Timing Risk - An investor who purchases Fund Shares other than on the first day of the options package and/or sells Fund Shares before the options package expires may not experience the 100% downside protection or upside participation in the Underlying ETF. The Fund's downside protection and upside participation of the Underlying ETF may only be available for investors who hold Fund Shares throughout the complete term of the options package. An investor can expect their Fund Shares to move generally in the same direction as the Underlying ETF during the one-year options package. However, Fund Shares may not experience the same price movement as the price movement of the Underlying ETF. During the duration of the option package, there may be periods of significant disparity between the Fund's NAV and the Underlying ETF's price performance. For example, if an investor purchases Fund Shares during an options package period at a time when the Underlying ETF's share price has increased from its price at the beginning of the options package period, the investor may not be 100% protected against Underlying ETF downside losses. In addition, if an investor purchases Fund Shares during an options package period at a time when the Underlying ETF's share price has increased from its price at the beginning of the options package period, that investor's cap will essentially be decreased from the stated Cap by the amount of the increase in the Underlying ETF's value.

• Large-Capitalization Investing Risk - Large-capitalization stocks as a group could fall out of favor with the market, which may cause the Fund to underperform funds that focus on other types of stocks. In addition, larger, more established companies may be unable to

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

respond quickly to new competitive challenges such as changes in technology and consumer preferences. Many larger companies also may not be able to attain the high growth rate of successful smaller companies, especially during extended periods of economic expansion.

• Liquidity Risk - Liquidity risk exists when particular investments are difficult to purchase or sell. The Fund's investments in illiquid securities may reduce the returns of the Fund because it may be unable to sell the illiquid securities at an advantageous time or price.

• Liquidity Risk -FLEX Options - In the event that trading in the underlying FLEX Options is limited or absent, the value of the Fund's FLEX Options may decrease. There is no guarantee that a liquid secondary trading market will exist for the FLEX Options. The trading in FLEX Options may be less deep and liquid than the market for certain other securities, including certain non-customized option contracts. In a less liquid market for the FLEX Options, terminating the FLEX Options may require the payment of a premium or acceptance of a discounted price and may take longer to complete. Additionally, the liquidation of a large number of FLEX Options may more significantly impact the price in a less liquid market. Further, the Fund requires a sufficient number of participants to facilitate the purchase and sale of options on an exchange to provide liquidity to the Fund for its FLEX Option positions. A less liquid trading market may adversely impact the value of the FLEX Options and the value of your investment.

• Market Maker Risk - If the Fund has lower average daily trading volumes, it may rely on a small number of third-party market makers to provide a market for the purchase and sale of Fund Shares. Any trading halt or other problem relating to the trading activity of these market makers could result in a dramatic change in the spread between the Fund's net asset value and the price at which the Fund Shares are trading on the Exchange, which could result in a decrease in value of the Fund Shares. In addition, decisions by market makers or authorized participants to reduce their role or step away from these activities in times of market stress could inhibit the effectiveness of the arbitrage process in maintaining the relationship between the underlying values of the Fund's portfolio securities and the Fund's market price. This reduced effectiveness could result in Fund Shares trading at a discount to net asset value and also in greater than normal intra-day bid-ask spreads for Fund Shares.

• Market Risk - The risk that the securities markets will increase or decrease in value is considered market risk and applies to any security. If there is a general decline in the stock or fixed-income market, it is possible your investment may lose value regardless of the individual results of the companies in which the Fund invests.

• New Fund Risk - The Fund is a recently organized investment company with a limited operating history. As a result, prospective investors have a limited track record or history on which to base their investment decision.

• Non-Diversification Risk - The Fund is classified as "non-diversified" under the 1940 Act. As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended (the "Code").

• Options Risk - The Fund's ability to close out its position as a purchaser or seller of an over-the-counter or exchange-listed put or call option is dependent, in part, upon the liquidity of the options market. There are significant differences between the securities and options markets that could result in an imperfect correlation among these markets, causing a given transaction not to achieve its objectives. The Fund's ability to utilize options successfully will depend on the ability of the Fund's investment adviser to predict pertinent market movements, which cannot be assured. The Fund may also purchase or write over-the-counter put or call options, which involves risks different from, and possibly greater than, the risks associated with exchange-listed put or call options. Over-the-counter put or call options may expose the Fund to the risk that a counterparty may be unable or unwilling to perform according to a contract, and that any deterioration in a counterparty's creditworthiness could adversely affect the instrument. In addition, the Fund may be exposed to a risk that losses may exceed the amount originally invested.

• Premium-Discount Risk - Fund Shares may trade above or below their NAV. The market prices of Fund Shares will generally fluctuate in accordance with changes in NAV as well as the relative supply of, and demand for, Fund Shares on the Exchange. The trading price of Fund Shares may deviate significantly from NAV during periods of market volatility.

• Secondary Market Trading Risk - Investors buying or selling Fund Shares in the secondary market will pay brokerage commissions or other charges imposed by brokers as determined by that broker. Brokerage commissions are often a fixed amount and may be a significant proportional cost for investors seeking to buy or sell relatively small amounts of Fund Shares. Although the Fund Shares are listed on the Exchange, there can be no assurance that an active or liquid trading market for them will develop or be maintained. In addition, trading in Fund Shares on the Exchange may be halted.

• Sector Risk - To the extent the Underlying ETF invests a significant portion of its assets in a particular sector, a greater portion of the Fund's performance may be affected by the general business and economic conditions affecting that sector. Each sector may share economic risk with the broader market, however there may be economic risks specific to each sector. As a result, returns from those sectors may trail returns from the overall stock market, and it is possible that the Underlying ETF may underperform the broader market.

• Tax Risk - The Fund intends to elect and to qualify each year to be treated as a regulated investment company ("RIC") under Subchapter M of the Internal Revenue Code of 1986, as amended (the "Code"). The federal income tax treatment of the securities in which the Fund may invest, including the Fund's option strategy, may not be clear or may be subject to recharacterization by the Internal Revenue Service. It could be more difficult to comply with the tax requirements applicable to RICs if the tax characterization of investments or the tax

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

treatment of the income from such investments were successfully challenged by the Internal Revenue Service. Any such failure to comply with the rules applicable to RICs could cause the Fund to fail to qualify as such. To qualify and maintain its status as a RIC, the Fund must meet certain income, diversification and distributions tests. For purposes of the diversification test, the identification of the issuer (or, in some cases, issuers) of a particular Fund investment can depend on the terms and conditions of that investment. In particular, there is no published Internal Revenue Service guidance or case law on how to determine the "issuer" of certain derivatives that the Fund will enter into. Based upon the language in the legislative history, the Fund intends to treat the issuer of an equity option as the referenced asset, which and to treat any income it may derive from an equity option as "qualifying income" under the provisions of the Code applicable to RICs. In the case of FLEX Options, as the referenced asset, which, assuming the referenced asset qualifies as a RIC, treating the issuer as the referenced asset would allow the Fund to count the FLEX Options as automatically diversified investments under the RIC diversification requirements. If the income is not qualifying income or the issuer of equity options, including FLEX Options. is not appropriately the referenced asset, the Fund may not qualify, or may be disqualified, as a RIC. If the Fund does not qualify as a RIC for any taxable year and certain relief provisions are not available, the Fund's taxable income will be subject to tax at the Fund level and to a further tax at the shareholder level when such income is distributed.

The Fund's investments in offsetting positions with respect to the Underlying ETF may affect the character of gains or losses realized by the Fund under the Code's "straddle" rules and may increase the amount of short-term capital gain realized by the Fund. Certain options the Fund holds may not qualify as "Section 1256 contracts" under Section 1256 of the Code, and disposition of such options will likely result in short-term or long-term capital gains or losses depending on the holding period.

There is a risk that if the offsetting FLEX Options are held by a single person that the IRS may take the position that the FLEX Options, viewed together, should be treated as a single debt instrument for federal tax purposes. The result of such a position would be that the Fund would fail the RIC diversification tests causing the RIC to be taxed as a C corporation, unless certain cure rights based upon reasonable cause may apply. The Fund has obtained an opinion of tax counsel that the FLEX Options should not be collapsed into a single instrument. However, such an opinion is not binding upon the IRS or the courts.

• Trading Issues Risk - Trading in Fund Shares on the Exchange may be halted due to market conditions or for reasons that, in the view of the Exchange, make trading in shares inadvisable. In addition, trading in Fund Shares on the Exchange is subject to trading halts caused by extraordinary market volatility pursuant to the Exchange's "circuit breaker" rules. There can be no assurance that the requirements of the Exchange necessary to maintain the listing of the Fund will continue to be met or will remain unchanged. The Fund may have difficulty maintaining its listing on the Exchange in the event the Fund's assets are small, the Fund does not have enough shareholders, or if the Fund is unable to proceed with creation and/or redemption orders.

• Underlying ETF Risk - The Fund invests in FLEX Options that reference an ETF, which subjects the Fund to certain of the risks of owning shares of an ETF as well as the types of instruments in which the Underlying ETF invests. The value of an ETF will fluctuate over time based on fluctuations in the values of the securities held by the ETF, which may be affected by changes in general economic conditions, expectations for future growth and profits, interest rates and the supply and demand for those securities. In addition, ETFs are subject to absence of an active market risk, premium/discount risk, tracking error risk and trading issues risk. Brokerage, tax and other expenses may negatively impact the performance of the Underlying ETF and, in turn, the value of the Fund's shares. An ETF that tracks an index may not exactly match the performance of the index due to cash drag, differences between the portfolio of the ETF and the components of the index, expenses and other factors.

• Valuation Risk - During periods of reduced market liquidity or in the absence of readily available market quotations for the holdings of the Fund, the ability of the Fund to value the FLEX Options may become more difficult. In market environments where there is reduced availability of reliable objective pricing data, the judgment of the Fund's investment adviser in determining the fair value of the security may play a greater role. While such determinations may be made in good faith, it may nevertheless be more difficult for the Fund to accurately assign a daily value.

Fund Performance

The Fund had not commenced operations as of the date of this prospectus. Once available, the Fund's performance information, and information that gives some indication of the risks of an investment in the Fund by comparing the Fund's performance with a broad measure of market performance, will be available on the Fund's website at: www.calamos.com. Past performance (before and after taxes) is not an indication of future performance.

Investment Adviser

Calamos Advisors LLC ("Calamos Advisors" or the "Adviser")

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

Portfolio Managers

Other Important Information Regarding Fund Shares

Portfolio Holdings. The Fund's portfolio holdings are disclosed on its website daily after the close of trading on the Exchange and prior to the opening of trading on the Exchange the following day. A description of the Fund's policies and procedures with respect to the disclosure of the Fund's portfolio holdings is available in the Fund's Statement of Additional Information ("SAI").

Premium/Discount Information. Information about the premiums and discounts at which the Fund's Shares have traded will be available at www.calamos.com.

Purchase and Sale of Fund Shares

The Fund will issue (or redeem) Fund Shares to certain institutional investors (typically market makers or other broker-dealers) only in large blocks of Fund Shares known as "Creation Units." Creation Unit transactions are conducted in exchange for the deposit or delivery of a designated portfolio of in-kind securities and/or cash.

Individual Fund Shares may only be purchased and sold on the Exchange, other national securities exchanges, electronic crossing networks and other alternative trading systems through your broker-dealer at market prices. Because Fund Shares trade at market prices rather than at net asset value ("NAV"), Fund Shares may trade at a price greater than NAV (premium) or less than NAV (discount). When buying or selling Fund Shares in the secondary market, you may incur costs attributable to the difference between the highest price a buyer is willing to pay to purchase Fund Shares (bid) and the lowest price a seller is willing to accept for Fund Shares (ask) (the "bid-ask spread"). Recent information regarding the Fund's NAV, market price, premiums and discounts, and bid-ask spreads is available at https://www.calamos.com/.

Tax Information

Net investment income and capital gains distributions you receive from the Fund generally are subject to federal income taxes and may also be subject to state and local taxes. The Fund intends to distribute net investment income and capital gains, if any, at least annually.

Payments to Broker-Dealers and Other Financial Intermediaries

If you purchase shares of the Fund through a broker-dealer or other financial intermediary (such as a bank), the Fund and its related companies may pay the intermediary for the sale of Fund Shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary's website for more information.

You can find the Fund's statutory prospectus and statement of additional information online at https://www.calamos.com/resources/.

Calamos S&P 500^®​ Structured Alt Protection ETF^TM​ - May

2020 Calamos Court
Naperville, IL 60563-2787
866.363.9219
www.calamos.com
811-22887

CPSMSUMPRO 050124