Filing by Investment Company (SEC Filing - 497K)

March 1, 2021, as amended September 17, 2021

Summary Prospectus

Calamos High Income Opportunities Fund

NASDAQ Symbol: CHYDX - Class A CCHYX - Class C CIHYX - Class I

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 https://www.calamos.com/resources/. You can also get this information at no cost by calling 800.582.6959 or by sending an e-mail request to [email protected]. The current prospectus dated March 1, 2021, as amended September 17, 2021, and statement of additional information dated March 1, 2021, as amended June 30, 2021 (and as each may be amended or supplemented), and the financial statements included in the Fund's recent report to shareholders, dated October 31, 2020, are incorporated by reference into this summary prospectus.

Beginning on March 1, 2021, as permitted by regulations adopted by the Securities and Exchange Commission, paper copies of the Fund's shareholder reports will no longer be sent by mail, unless you specifically request paper copies of the reports from the Fund or from your financial intermediary. Instead, the reports will be made available on a website, and you will be notified by mail each time a report is posted and provided with a website link to access the report.

If you already elected to receive shareholder reports electronically, you will not be affected by this change and you need not take any action. You may elect to receive shareholder reports and other communications from the Fund electronically by calling 800.582.6959. If you own these shares through a financial intermediary, you may contact your financial intermediary.

You may elect to receive all future reports in paper free of charge. You can inform the Fund that you wish to continue receiving paper copies of your shareholder reports by calling 800.582.6959. If you own these shares through a financial intermediary, you may contact your financial intermediary or follow instructions included with this disclosure to elect to continue to receive paper copies of your share-holder reports. Your election to receive reports in paper will apply to all funds held with the fund complex or your financial intermediary.

Investment Objective

Calamos High Income Opportunities Fund's primary objective is the highest level of current income obtainable with reasonable risk. Its secondary objective is capital gain, where consistent with the Fund's primary objective.

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. Investors may pay other fees, such as brokerage commissions and/or other forms of compensation to a financial intermediary, which are not reflected in the tables or the examples below. You may qualify for sales charge discounts on purchases of Class A shares if you and your family invest, or agree to invest in the future, at least $100,000 in Calamos Funds. More information about these and other discounts is available from your financial professional and under 'Fund Facts - What classes of shares do the Funds offer?' on page 129 of the Fund's prospectus, in the Appendix to this prospectus and 'Share Classes and Pricing of Shares' on page 87 of the Fund's statement of additional information.

Shareholder Fees (fees paid directly from your investment):

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

1 The Fund's investment advisor has contractually agreed to reimburse Fund expenses through March 1, 2023 to the extent necessary so that Total Annual Fund Operating Expenses (excluding taxes, interest, short interest, short dividend expenses, brokerage commissions, acquired fund fees and expenses, and extra- ordinary expenses, if any) of Class A, Class C, and Class I are limited to 1.00%, 1.75%, and 0.75% of average net assets, respectively. Calamos Advisors may recapture previously waived expense amounts within the same fiscal year for any day where the respective Fund's expense ratio falls below the contractual expenses limit up to the expense limit for that day. This undertaking is binding on Calamos Advisors and any of its successors and assigns. This agreement is not terminable by either party.

HIOPRO 09/21

Calamos High Income Opportunities Fund

Example

This example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then either redeem or do not redeem your shares at the end of the reflected time periods. The example also assumes that your investment has a 5% return each year, that all dividends and capital gain distributions are reinvested, that you pay a maximum initial or contingent deferred sales charge and that the Fund's operating expenses remain the same. Any applicable fee waivers and/or expense reimbursements are reflected in the below examples for the period through March 1, 2023 only. Although your actual performance and costs may be higher or lower, based on these assumptions, your costs would be:

You would pay the following expenses if you redeemed your shares at the end of the period:

You would pay the following expenses if you did not redeem your shares:

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 the annual fund operating expenses or in the example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 51.8% of the average value of its portfolio.

Principal Investment Strategies

The Fund invests primarily in a diversified portfolio of high yield fixed-income securities (often referred to as 'junk bonds') issued by both U.S. and foreign companies. Although not a principal investment strategy, the Fund may invest in securities of issuers in emerging markets to a significant extent.

The high yield fixed-income securities in which the Fund intends to invest have lower credit ratings than investment grade securities (those rated BBB or higher by S&P, or Baa or higher by Moody's). However, junk bonds typically offer a significantly higher yield, as well as greater risks, than investment grade securities. S&P's and Moody's ratings are used only as preliminary indicators of investment quality. The Fund also uses its own credit research and analysis. The Fund's investment adviser seeks to lower the risks of investing in stocks by using a 'top-down approach' of diversification by company, industry, sector, country and currency and focusing on macro-level investment themes, such as large-scale events on the country-wide, continental and global scale, implementing opportunistic investment strategies to capitalize on geopolitical trends.

The Fund may invest in both convertible (including synthetic convertible) and non-convertible high yield bonds. Convertible debt securities are exchangeable for equity securities of the issuer at a predetermined price, and typically offer greater appreciation potential than non-convertible debt securities. References in this prospectus to the Fund 'investing' in any instrument, security or strategy include direct or indirect investment, including gaining exposure through derivatives, master limited partnerships or other investment companies.

A synthetic convertible instrument is a financial instrument (or two or more securities held in tandem) that is designed to simulate the economic characteristics of a convertible security through the combined features of a debt instrument and a security providing an option on an equity security. The Fund may establish a synthetic convertible instrument by combining fixed-income securities (which may be either convertible or non-convertible) with the right to acquire equity securities. In establishing a synthetic instrument, the Fund may combine a basket of fixed-income securities with a basket of warrants or options that together produce economic characteristics similar to a convertible security. Within each basket of fixed-income securities and warrants or options, different companies may issue the fixed-income and convertible components, which may be purchased separately and at different times.

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 objectives. 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 of investing in the Fund include:

Calamos High Income Opportunities Fund

• Convertible Securities Risk - The value of a convertible security is influenced by changes in interest rates, with investment value declining as interest rates increase and increasing as interest rates decline. The credit standing of the issuer and other factors also may have an effect on the convertible security's investment value.

• Debt Securities Risk - Debt securities are subject to various risks, including interest rate risk, credit risk and default risk.

• Interest Rate Risk - The value of debt securities generally decreases in periods when interest rates are rising. In addition, interest rate changes typically have a greater effect on prices of longer-term debt securities than shorter term debt securities. Recent fixed-income market events, including increases in volatility and interest rates, may expose the Fund to heightened interest rate risk and volatility.

• Credit Risk - A debt security could deteriorate in quality to such an extent that its rating is downgraded or its market value declines relative to comparable securities. If the Fund holds securities that have been downgraded, or that default on payment, the Fund's performance could be negatively affected.

• Default Risk - A company that issues a debt security may be unable to fulfill its obligation to repay principal and interest. The lower a bond is rated, the greater its default risk. To the extent the Fund holds securities that have been downgraded, or that default on payment, its performance could be negatively affected.

• Derivatives Risk - Derivatives are instruments, such as 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 the derivatives 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.

• Emerging Markets Risk - Emerging market countries may have relatively unstable governments and economies based on only a few industries, which may cause greater instability. The value of emerging market securities will likely be particularly sensitive to changes in the economies of such countries. These countries are also more likely to experience higher levels of inflation, deflation or currency devaluations, which could hurt their economies and securities markets.

• Equity Securities Risk - The securities markets are volatile, and the market prices of the Fund'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 Fund fall, the value of your investment in the Fund will decline.

• Foreign Securities Risk - There are special risks associated with investing in foreign securities that are not typically associated with investing in U.S. companies. These risks include fluctuations in the exchange rates of foreign currencies that may affect the U.S. dollar value of a security, and the possibility of substantial price volatility as a result of political and economic instability in the foreign country. Other risks of investing in foreign securities include: less public information about issuers of securities, different securities regulation, different accounting, auditing and financial reporting standards and less liquidity in foreign markets than in U.S. markets.

• Futures and Forward Contracts Risk - Futures contracts provide for the future sale by one party and purchase by another of a specific asset at a specific time and price (with or without delivery required). Futures contracts are standardized contracts traded on a recognized exchange. An option on a futures contract gives the purchaser the right, in exchange for a premium, to assume a position in a futures contract at a specified exercise price during the term of the option. Futures and forward contracts are subject to counterparty risk, meaning that the party with whom the Fund enters into the derivatives transaction (the clearinghouse or the broker holding the Fund's position for a futures contract or the counterparty for a forward contract) may experience a significant credit event and/or may be unwilling or unable to make timely settlement payments or otherwise honor its obligations.

• High Yield Risk - High yield securities and unrated securities of similar credit quality (commonly known as 'junk bonds') are subject to greater levels of credit and liquidity risks. High yield securities are considered primarily speculative with respect to the issuer's continuing ability to make principal and interest payments.

• 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.

• MLP Risk - Investments in securities of MLPs involve risk that differ from investments in common stock, including risks related to limited control and limited rights to vote on matters affecting the MLP, risks related to the potential conflicts of interest between the MLP and the MLP's general partners, cash flow risks, dilution risks and risks related to the general partners right to require unit holders to sell their common units at an undesirable time or price.

• MLP Tax Risk - MLPs generally do not pay federal income tax at the partnership level. Rather, each partner is allocated a share of the partnerships' income, gains, losses, deductions and credits. A change in current tax law, or a change in the underlying business of an MLP, could result in an MLP being treated as a corporation, instead of a partnership, for federal income tax purposes, which would result

Calamos High Income Opportunities Fund

in such MLP being required to pay income tax on its taxable income. This would have the effect of reducing the amount of cash available for distribution by the MLP, potentially reducing the value of the Fund's investment and consequently your investment in the Fund.

• MLP Liquidity Risk - Although common units of MLPs trade on the NYSE, the NASDAQ and Amex, certain MLP securities trade less frequently than those of larger companies due to their smaller capitalization. As a result, the price of such MLPs may display abrupt and erratic movements at times. Additionally it may be more difficult for the Fund to buy and sell significant amounts of such securities without unfavorable impact on prevailing market process. As a result, these securities may be difficult to dispose of at a fair price when the Adviser desires to do so. This may adversely affect the Fund's ability to take advantage of other market opportunities or make dividend distributions.

• Equity Securities of MLPs Risk - MLP common units, like other equity securities, can be affected by macro-economic and other factors affecting the stock market in general, expectations of interest rates, investor sentiment towards an issuer or certain market sector, changes in a particular issuer's financial condition, or unfavorable or unanticipated poor performance of a particular issuer (in the case of MLPs, generally measured in terms of distributable cash flow). Prices of common units of individual MLPs, like the prices other equity securities, also can be affected by fundamentals unique to the partnership or company, including earnings power and coverage ratios.

• Mortgage-related and Other Asset-backed Securities Risk - In addition to general fixed-income instrument risks, mortgage-related and asset-backed securities are subject to extension risk and prepayment risk.

• Extension Risk - Rising interest rates tend to extend the duration of mortgage-related securities, making them more sensitive to changes in interest rates. As a result, in a period of rising interest rates, if the Fund holds mortgage-related securities, it may exhibit additional volatility.

• Prepayment Risk - When interest rates decline, the value of mortgage-related securities with prepayment features may not increase as much as other fixed-income securities because borrowers may pay off their mortgages sooner than expected. In addition, the potential impact of prepayment on the price of asset-backed and mortgage-backed securities may be difficult to predict and result in greater volatility.

• Options Risk - 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 Calamos Advisors' ability to predict pertinent market movements, which cannot be assured.

• Other Investment Companies (including ETFs) Risk - The Fund may invest in the securities of other investment companies to the extent that such investments are consistent with the Fund's investment objective and the policies are permissible under the 1940 Act. Under the 1940 Act, the Fund may not acquire the securities of other domestic or non-U.S. investment companies if, as a result, (1) more than 10% of the Fund's total assets would be invested in securities of other investment companies, (2) such purchase would result in more than 3% of the total outstanding voting securities of any one Investment company being held by the Fund or (3) more than 5% of the Fund's total assets would be invested in any one investment company. These limitations do not apply to the purchase of shares of money market funds or of any investment company in connection with a merger, consolidation, reorganization or acquisition of substantially all the assets of another investment company, or to purchases of investment companies done in accordance with SEC exemptive relief or rules. Investments in the securities of other investment companies, including ETFs, may involve duplication of advisory fees and certain other expenses. By investing in another investment company or ETF, the Fund becomes a shareholder thereof. As a result, Fund shareholders indirectly bear the Fund's proportionate share of the fees and expenses indirectly paid by shareholders of the other investment company or ETF, in addition to the fees and expenses Fund shareholders bear in connection with the Fund's own operations. If the investment company or ETF fails to achieve its investment objective, the value of the Fund's investment will decline, adversely affecting the Fund's performance. In addition, closed end investment company and ETF shares potentially may trade at a discount or a premium and are subject to brokerage and other trading costs, which could result in greater expenses to the Fund. In addition, the Fund may engage in short sales of the securities of other investment companies. When the Fund shorts securities of another investment company, it borrows shares of that investment company which it then sells. The Fund closes out a short sale by purchasing the security that it has sold short and returning that security to the entity that lent the security.

• Portfolio Selection Risk - The value of your investment may decrease if the investment adviser's judgment about the attractiveness, value or market trends affecting a particular security, issuer, industry, or sector or about market movements is incorrect.

• RIC Qualification Risk - To qualify for treatment as a regulated investment company ('RIC') under the Code, the Fund must meet certain income source, asset diversification and annual distribution requirements. The Fund's MLP investments may make it more difficult for the Fund to meet these requirements. The asset diversification requirements include a requirement that, at the end of each quarter of each taxable year, not more than 25% of the value of the Fund's total assets is invested in the securities (including debt securities) of one or more qualified publicly traded partnerships. The Fund anticipates that the MLPs in which it invests will be qualified publicly traded partnerships. If the Fund's MLP investments exceed this 25% limitation then the Fund would not satisfy the diversification requirements and could fail to qualify as a RIC. If, in any year, the Fund fails to qualify as a RIC for any reason, the Fund would be taxed as an ordinary corporation and would become (or remain) subject to corporate income tax. The resulting corporate taxes could substantially reduce the Fund's net assets, the amount of income available for distribution and the amount of Fund distributions.

Calamos High Income Opportunities Fund

• Rule 144A Securities Risk - The Fund may invest in securities that are issued and sold through transactions under Rule 144A of the Securities Act of 1933. Under the supervision of its board of trustees, the Fund will determine whether Rule 144A Securities are illiquid. If qualified institutional buyers are unwilling to purchase these Rule 144A Securities, the percentage of the Fund's assets invested in illiquid securities would increase. Typically, the Fund purchases Rule 144A Securities only if the Fund's adviser has determined them to be liquid. If any Rule 144A Security held by the Fund should become illiquid, the value of the security may be reduced and a sale of the security may be more difficult.

• Securities Lending Risk - The Fund may lend its portfolio securities to broker-dealers and banks in order to generate additional income for the Fund. Any such loan must be continuously secured by collateral in cash or cash equivalents maintained on a current basis in an amount at least equal to the market value of the securities loaned by the Fund. In the event of bankruptcy or other default of a borrower of portfolio securities, the Fund could experience both delays in liquidating the loan collateral or recovering the loaned securities and losses, including (a) possible decline in the value of the collateral or in the value of the securities loaned during the period while the Fund seeks to enforce its rights thereto, (b) possible subnormal levels of income and lack of access to income during this period, and (c) expenses of enforcing its rights. In an effort to reduce these risks, the Fund's securities lending agent monitors, and reports to Calamos Advisors on, the creditworthiness of the firms to which a Fund lends securities. The Fund may also experience losses as a result of a diminution in value of its cash collateral investments.

• Synthetic Convertible Instruments Risk - The value of a synthetic convertible instrument will respond differently to market fluctuations than a convertible security because a synthetic convertible instrument is composed of two or more separate securities, each with its own market value. In addition, if the value of the underlying common stock or the level of the index involved in the convertible component falls below the exercise price of the warrant or option, the warrant or option may lose all value.

• Tax Risk - The federal income tax treatment of convertible securities or other securities in which the Fund may invest 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 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.

• U.S. Government Security Risk - Some securities issued by U.S. Government agencies or government sponsored enterprises are not backed by the full faith and credit of the U.S. and may only be supported by the right of the agency or enterprise to borrow from the U.S. Treasury. There can be no assurance that the U.S. Government will always provide financial support to those agencies or enterprises.

Fund Performance

The following bar chart and table indicate the risks of investing in the Fund by showing changes in the Fund's performance from calendar year to calendar year and how the Fund's average annual total returns compare with those of a broad measure of market performance. All returns include the reinvestment of dividends and distributions. As always, please note that the Fund's past performance (before and after taxes) cannot predict how it will perform in the future. Updated performance information is available at no cost by visiting www.calamos.com or by calling 800.582.6959.

CLASS I* ANNUAL TOTAL RETURN FOR YEARS ENDED 12.31

* Annual returns for Class I are provided because Class I shares represent the largest percentage of assets in the Calamos Family of Funds.

Average Annual Total Returns as of 12.31.20

The following table shows how the Fund's average annual performance (before and after taxes) for the one-, five- and ten-year periods ended December 31, 2020 and since the Fund's inception compared with broad measures of market performance. 'Since Inception' returns shown for the index are returns since the inception of the Fund's Class A shares, or since the nearest subsequent month end when comparative index data is available only for full monthly periods. The after-tax returns show the impact of assumed federal income taxes on an investment in the Fund. 'Return After Taxes on Distributions' shows the effect of taxable distributions, but assumes that you still hold the Fund shares

Calamos High Income Opportunities Fund

at the end of the period and so do not have any taxable gain or loss on your investment. 'Return After Taxes on Distributions and Sale of Fund Shares' shows the effect of taxable distributions and any taxable gain or loss that would be realized if the Fund shares were purchased at the beginning and sold at the end of the specified period.

The after-tax returns are shown only for Class I shares, and are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their Fund shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns for classes other than Class I will vary from returns shown for Class I. 'Return After Taxes on Distributions and Sale of Fund Shares' may be higher than other returns for the same period due to a tax benefit of realizing a capital loss on the sale of Fund shares.

AVERAGE ANNUAL TOTAL RETURNS - FOR THE PERIODS ENDED 12.31.20

* Returns after taxes for Class I are provided because Class I shares represent the largest percentage of assets in the Calamos Family of Funds.

Investment Adviser

Calamos Advisors LLC

Other Important Information Regarding Fund Shares

For important information about purchase and sale of Fund shares, tax information, and financial intermediary compensation, please turn to 'Other Important Information Regarding Fund Shares' on page 109 of the prospectus.

Buying and Redeeming Fund Shares

Minimum Initial Investment

Classes A and C: $2,500/$500 for IRA
Class I: $1,000,000

Minimum Additional Investment

Classes A and C: $50
Class I: None

Calamos High Income Opportunities Fund

To Place Orders

Please contact your broker, benefit plan record-keeper, or other intermediary, or to place your order directly, contact the Fund's transfer agent, U.S. Bank Global Fund Services, toll-free at the number noted below for further instructions:
U.S. Bank Global Fund Services
P.O. Box 701
Milwaukee, WI 53201
Phone: 800.582.6959

Transaction Policies

The Funds' shares are redeemable. In general, investors may purchase, redeem, or exchange Fund shares on any day the New York Stock Exchange is open by written request (to the address noted above), by wire transfer, by telephone (at the number noted above), or through a financial intermediary, depending on how the shares are held. Orders to buy and redeem shares are processed at the next net asset value (share price or 'NAV') to be calculated only on days when the New York Stock Exchange is open for regular trading.

Class I may not be available for purchase directly from the Funds. Please contact us at 800.582.6959 to inquire further about such availability.

Tax Information

The Funds' distributions will generally be taxable as ordinary income or capital gains, except when your investment is in an IRA, 401(k) or other tax-advantaged investment plan. Any distributions from a retirement account or 401(k) plan may be taxed as ordinary income when withdrawn from such account or plan. Special tax rules apply to investments held through defined contribution plans and other tax-qualified plans.

Payments to Broker-Dealers and Other Financial Intermediaries

If you purchase shares of a 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.

Click here to view the Fund's statutory prospectus or statement of additional information.

2020 Calamos Court
Naperville, IL 60563-2787
800.582.6959
www.calamos.com
811-05433