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0001097519 cfst:C000122569Member 2016-01-01 2025-12-31 0001097519 cfst:C000254316Member 2016-01-01 2025-12-31 iso4217:USD pure 0001097519 false 485BPOS 2026-03-31 0.0146 0.0566 0.0079 0.0047 0.0482 0.0326 0.0048 -0.0493 0.0704 0.0594 Best and Worst Quarterly Returns During the Period Shown in the Bar Chart Best 2nd Quarter 2020 6.40% Worst 1st Quarter 2020 -5.74% N-1A COLUMBIA FUNDS SERIES TRUST 2026-08-01 Summary of the Fund Investment Objective <div style="margin-top:4pt;">Columbia Short Term Bond Fund (the Fund) seeks current income, consistent with minimal fluctuation of principal.</div> Fees and Expenses of the Fund <div style="margin-top:4pt;">This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below. You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information is available about these and other sales charge discounts and waivers from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 28 of the Fund’s prospectus, in Appendix A to the prospectus beginning on page A-1 and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1. </div> You may qualify for sales charge discounts if you and members of your immediate family invest, or agree to invest in the future, at least $50,000 in certain classes of shares of eligible funds distributed by Columbia Management Investment Distributors, Inc. (the Distributor). More information is available about these and other sales charge discounts and waivers from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 28 of the Fund’s prospectus, in Appendix A to the prospectus beginning on page A-1 and in Appendix S to the Statement of Additional Information (SAI) under Sales Charge Waivers beginning on page S-1. 50000 Shareholder Fees (fees paid directly from your investment) 0.0100 0 0 0 0 0 0.0100 0.0100 0 0 0 0 Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment) 0.0042 0.0042 0.0042 0.0042 0.0042 0.0042 0.0025 0.0080 0.0000 0.0000 0.0000 0.0000 0.0011 0.0011 0.0011 0.0008 0.0003 0.0011 0.0078 0.0133 0.0053 0.0050 0.0045 0.0053 -0.0007 -0.0007 -0.0007 -0.0011 -0.0007 -0.0007 0.0071 0.0126 0.0046 0.0039 0.0038 0.0046 This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions. This charge applies to redemptions within 12 months after purchase, with certain limited exceptions. “Total annual Fund operating expenses” include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than the ratio of expenses to average net assets shown in the Financial Highlights section of this prospectus because the ratio of expenses to average net assets does not include acquired fund fees and expenses. July 31, 2027 Example <div style="margin-top:6pt;">The following 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 illustrates the hypothetical expenses that you would incur over the time periods indicated, and assumes that: </div><div> <div style="clear:both;margin-top:4.00pt;position:relative;width:100%;"> <div style="float:left;line-height:10pt;margin-left:6pt;text-align:left;width:4.45pt;">■</div> <div style="float:left;line-height:12pt;margin-left:6.55pt;text-align:left;width:494.00pt;">you invest $10,000 in the applicable class of Fund shares for the periods indicated, </div> </div> <div style="clear:both;position:relative;"> </div> </div><div> <div style="clear:both;margin-top:4.00pt;position:relative;width:100%;"> <div style="float:left;line-height:10pt;margin-left:6pt;text-align:left;width:4.45pt;">■</div> <div style="float:left;line-height:12pt;margin-left:6.55pt;text-align:left;width:494.00pt;">you redeem all your shares at the end of the period, </div> </div> <div style="clear:both;position:relative;"> </div> </div><div> <div style="clear:both;margin-top:4.00pt;position:relative;width:100%;"> <div style="float:left;line-height:10pt;margin-left:6pt;text-align:left;width:4.45pt;">■</div> <div style="float:left;line-height:12pt;margin-left:6.55pt;text-align:left;width:494.00pt;">your investment has a 5% return each year, and </div> </div> <div style="clear:both;position:relative;"> </div> </div><div> <div style="clear:both;margin-top:4.00pt;position:relative;width:100%;"> <div style="float:left;line-height:10pt;margin-left:6pt;text-align:left;width:4.45pt;">■</div> <div style="float:left;line-height:12pt;margin-left:6.55pt;text-align:left;width:494.00pt;">the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expenses table above.</div> </div> <div style="clear:both;position:relative;"> </div> </div><div style="margin-top:6pt;">Class C shares’ 10-year cost examples below reflect the Class C shares' 8-year conversion policy. Since the waivers and/or reimbursements shown in the Annual Fund Operating Expenses table above expire as indicated in the preceding table, they are only reflected in the 1 year example and the first year of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be: </div> 172 172 340 340 522 522 1050 1050 228 415 722 1444 128 415 722 1444 47 47 163 163 289 289 658 658 40 40 149 149 269 269 618 618 39 39 137 137 245 245 560 560 47 47 163 163 289 289 658 658 Portfolio Turnover <div style="margin-top:4pt;">The Fund may pay 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. During the most recent fiscal year, the Fund’s portfolio turnover rate was 76% of the average value of its portfolio.</div> 0.76 Principal Investment Strategies <div style="margin-top:4pt;">Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in bonds, including debt instruments issued by the U.S. Government and its agencies, debt securities issued by corporations, mortgage- and other asset-backed securities, and dollar-denominated securities issued by foreign governments, companies or other entities. The Fund also invests at least 65% of its total assets in securities that, at the time of purchase, are rated investment grade or are unrated but determined to be of comparable quality (at June 30, 2026, the Fund held 90.10% in securities of investment grade quality, exclusive of the Fund’s investments in cash and cash equivalents, which was 0.49%).</div><div style="margin-top:4pt;">The Fund may invest in mortgage- and other asset-backed securities. The Fund may invest in floating rate debt securities, which have interest rates that adjust or “float” periodically.</div><div style="margin-top:4pt;">The Fund may invest in privately placed and other securities or instruments that are purchased and sold pursuant to Rule 144A or other exemptions under the Securities Act of 1933, as amended, subject to certain regulatory restrictions.</div><div style="line-height:12.0pt;text-align:left;">The Fund may invest in derivatives, such as futures (including interest rate futures) for both hedging and non-hedging purposes, including, for example, to seek to enhance returns or as a substitute for a position in an underlying asset, as well as to manage duration.</div><div style="margin-top:4pt;">The Fund may purchase or sell securities on a when-issued, delayed delivery or forward commitment basis. Such securities may include mortgage-backed securities acquired or sold in the “to be announced” (TBA) market and those in a dollar roll transaction.</div><div style="margin-top:4pt;">The Fund’s investment strategy may involve the frequent trading of portfolio securities.</div><div style="margin-top:4pt;">Under normal circumstances, the Fund’s dollar-weighted average effective maturity will be three years or less, and its duration will be three years or less.</div> <div style="margin-top:4pt;">Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in bonds, including debt instruments issued by the U.S. Government and its agencies, debt securities issued by corporations, mortgage- and other asset-backed securities, and dollar-denominated securities issued by foreign governments, companies or other entities. The Fund also invests at least 65% of its total assets in securities that, at the time of purchase, are rated investment grade or are unrated but determined to be of comparable quality (at June 30, 2026, the Fund held 90.10% in securities of investment grade quality, exclusive of the Fund’s investments in cash and cash equivalents, which was 0.49%).</div> Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in bonds, including debt instruments issued by the U.S. Government and its agencies, debt securities issued by corporations, mortgage- and other asset-backed securities, and dollar-denominated securities issued by foreign governments, companies or other entities. There is no assurance that the Fund will achieve its investment objective and you may lose money. An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. <div style="margin-top:4pt;">Active Management Risk. Due to its active management, the Fund could underperform its benchmark index and/or other funds with similar investment objectives and/or strategies.</div> <div style="margin-top:4pt;">Changing Distribution Level Risk. The Fund normally expects to receive income which may include interest, dividends and/or capital gains, depending upon its investments. The distribution amounts paid by the Fund will vary and generally depend on the amount of income the Fund earns (less expenses) on its portfolio holdings, and capital gains or losses it recognizes. A decline in the Fund’s income or net capital gains arising from its investments may reduce its distribution level.</div> <div style="margin-top:4pt;">Counterparty Risk. Counterparty risk is the risk that a counterparty to a transaction in a financial instrument held by the Fund or by a special purpose or structured vehicle invested in by the Fund may become insolvent or otherwise fail to perform its obligations. As a result, the Fund may obtain no or limited recovery of its investment, and any recovery may be significantly delayed.</div> <div style="margin-top:4pt;">Credit Risk. Credit risk is the risk that the value of debt instruments may decline if the issuer thereof defaults or otherwise becomes unable or unwilling, or is perceived to be unable or unwilling, to honor its financial obligations, such as making payments to the Fund when due. Credit rating agencies, such as S&P Global Ratings, Moody’s Investors Service, Inc. (Moody’s Ratings), Fitch Ratings, Inc. (Fitch), Morningstar DBRS (DBRS) and Kroll Bond Rating Agency, LLC (KBRA), assign credit ratings to certain debt instruments to indicate their credit risk. A rating downgrade by such agencies can negatively impact the value of such instruments. Lower-rated or unrated instruments held by the Fund may present increased credit risk as compared to higher-rated instruments. Non-investment grade debt instruments may be subject to greater price fluctuations and are more likely to experience a default than investment grade debt instruments and therefore may expose the Fund to increased credit risk. If the Fund purchases unrated instruments, or if the ratings of instruments held by the Fund are lowered after purchase, the Fund will depend on analysis of credit risk more heavily than usual.</div> <div style="margin-top:4pt;">Derivatives Risk. Derivatives may involve significant risks. Derivatives are financial instruments with a value in relation to, or derived from, the value of an underlying asset(s) or other reference, such as an index, rate or other economic indicator (each an underlying reference). Derivatives may include those that are privately placed or otherwise exempt from SEC registration, including certain Rule 144A eligible securities. Derivatives could result in Fund losses if the underlying reference does not perform as anticipated. Use of derivatives is a highly specialized activity that can involve investment techniques, risks, and tax planning different from those associated with more </div><div style="line-height:12.0pt;text-align:left;">traditional investment instruments. The Fund’s derivatives strategy may not be successful, and use of certain derivatives could result in substantial, potentially unlimited, losses to the Fund regardless of the Fund’s actual investment. A relatively small movement in the price, rate or other economic indicator associated with the underlying reference may result in substantial losses for the Fund. Derivatives may be more volatile than other types of investments. The value of derivatives may be influenced by a variety of factors, including national and international political and economic developments. Potential changes to the regulation of the derivatives markets may make derivatives more costly, may limit the market for derivatives, or may otherwise adversely affect the value or performance of derivatives. Derivatives can increase the Fund’s risk exposure to underlying references and their attendant risks, such as credit risk, market risk, foreign currency risk and interest rate risk, while potentially exposing the Fund to correlation risk, counterparty risk, hedging risk, inflation risk, leverage risk, liquidity risk, pricing risk and volatility risk.</div> <div style="margin-top:4pt;">Derivatives Risk – Futures Contracts Risk. A futures contract is an exchange-traded derivative transaction between two parties in which a buyer (holding the “long” position) agrees to pay a fixed price (or rate) at a specified future date for delivery of an underlying reference from a seller (holding the “short” position). The seller hopes that the market price on the delivery date is less than the agreed upon price, while the buyer hopes for the contrary. Certain futures contract markets are highly volatile, and futures contracts may be illiquid. Futures exchanges may limit fluctuations in futures contract prices by imposing a maximum permissible daily price movement. The Fund may be disadvantaged if it is prohibited from executing a trade outside the daily permissible price movement. At or prior to maturity of a futures contract, the Fund may enter into an offsetting contract and may incur a loss to the extent there has been adverse movement in futures contract prices. The liquidity of the futures markets depends on participants entering into offsetting transactions rather than making or taking delivery. To the extent participants make or take delivery, liquidity in the futures market could be reduced. Because of the low margin deposits normally required in futures trading, it is possible that the Fund may employ a high degree of leverage in the portfolio. As a result, a relatively small price movement in a futures contract may result in substantial losses to the Fund, exceeding the amount of the margin paid. For certain types of futures contracts, losses are potentially unlimited. Futures markets are highly volatile, and the use of futures may increase the volatility of the Fund’s NAV. Futures contracts executed (if any) on foreign exchanges may not provide the same protection as U.S. exchanges. Futures contracts can increase the Fund’s risk exposure to underlying references and their attendant risks, such as credit risk, market risk, foreign currency risk and interest rate risk, while potentially exposing the Fund to correlation risk, counterparty risk, hedging risk, inflation risk, leverage risk, liquidity risk, pricing risk and volatility risk.</div> <div style="margin-top:4pt;">Fixed Income Instruments Risk. The Fund is subject to the general risks and considerations associated with investing in debt securities, including the risk that issuers will fail to make timely payments of principal or interest or default altogether. Lower-rated securities in which the Fund may invest may be more volatile and may decline more in price in response to negative issuer developments or general economic news than higher rated securities. In addition, as interest rates rise, the Fund’s investments typically will lose value.</div> <div style="margin-top:4pt;">Foreign Securities Risk. Investments in or exposure to securities of foreign companies may involve heightened risks relative to investments in or exposure to securities of U.S. companies. Investing in securities of foreign companies subjects the Fund to the risks associated with an issuer’s (and any of its related companies’) country of organization and places of business operations, including risks related to political, regulatory, economic, social, diplomatic and other conditions or events (including, for example, military confrontations and actions, war, other conflicts, terrorism and disease/virus outbreaks and epidemics) occurring in the country or region, as well as risks associated with less developed custody and settlement practices. Foreign securities may be more volatile and less liquid than securities of U.S. companies and are subject to the risks associated with potential imposition of economic and other sanctions against a particular foreign country, its nationals or industries or businesses within the country. In addition, foreign governments may impose withholding or other taxes on the Fund’s income, capital gains or proceeds from the disposition of foreign securities, which could reduce the Fund’s return on such securities.</div> <div style="margin-top:4pt;">Forward Commitments on Mortgage-Backed Securities (including Dollar Rolls) Risk. When purchasing mortgage-backed securities in the “to be announced” (TBA) market (MBS TBAs), the seller agrees to deliver mortgage-backed securities for an agreed upon price on an agreed upon date, but may make no guarantee as to the specific securities to be delivered. In lieu of taking delivery of mortgage-backed securities, the Fund could enter into dollar rolls, which </div><div style="line-height:12.0pt;text-align:left;">are transactions in which the Fund sells securities to a counterparty and simultaneously agrees to purchase those or similar securities in the future at a predetermined price. Dollar rolls involve the risk that the market value of the securities the Fund is obligated to repurchase may decline below the repurchase price, or that the counterparty may default on its obligations. These transactions may also increase the Fund’s portfolio turnover rate. If the Fund reinvests the proceeds of the security sold, the Fund will also be subject to the risk that the investments purchased with such proceeds will decline in value (a form of leverage risk). MBS TBAs and dollar rolls are subject to the risk that the counterparty to the transaction may not perform or be unable to perform in accordance with the terms of the instrument.</div> <div style="margin-top:4pt;">Frequent Trading Risk. The portfolio managers may actively and frequently trade investments in the Fund's portfolio to carry out its investment strategies. Frequent trading of investments increases the possibility that the Fund, as relevant, will realize taxable capital gains (including short-term capital gains, which are generally taxable to shareholders at higher rates than long-term capital gains for U.S. federal income tax purposes), which could reduce the Fund's after-tax return. Frequent trading can also mean higher brokerage and other transaction costs, which could reduce the Fund's return. The trading costs and tax effects associated with portfolio turnover may adversely affect the Fund’s performance.</div> <div style="margin-top:4pt;">High-Yield Investments Risk. Securities and other debt instruments held by the Fund that are rated below investment grade (commonly called “high-yield” or “junk” bonds) and unrated debt instruments of comparable quality expose the Fund to a greater risk of loss of principal and income than a fund that invests solely or primarily in investment grade debt instruments. In addition, these investments have greater price fluctuations, are less liquid and are more likely to experience a default than higher-rated debt instruments. High-yield debt instruments are considered to be predominantly speculative with respect to the issuer’s capacity to pay interest and repay principal.</div> <div style="margin-top:4pt;">Interest Rate Risk. Interest rate risk is the risk of losses attributable to changes in interest rates. In general, if interest rates rise, the values of debt instruments tend to fall, and if interest rates fall, the values of debt instruments tend to rise. Changes in the value of a debt instrument usually will not affect the amount of income the Fund receives from it but will generally affect the value of your investment in the Fund. Changes in interest rates may also affect the liquidity of the Fund’s investments in debt instruments. In general, the longer the maturity or duration of a debt instrument, the greater its sensitivity to changes in interest rates. For example, a three-year duration means a bond is expected to decrease in value by 3% if interest rates rise 1% and increase in value by 3% if interest rates fall 1%. Interest rate declines also may increase prepayments of debt obligations, which, in turn, would increase prepayment risk. The Fund is subject to the risk that the income generated by its investments may not keep pace with inflation. Actions by governments and central banking authorities can result in increases or decreases in interest rates. Higher periods of inflation could lead such authorities to raise interest rates. Such actions may negatively affect the value of debt instruments held by the Fund, resulting in a negative impact on the Fund's performance and NAV. Any interest rate increases could cause the value of the Fund’s investments in debt instruments to decrease. Rising interest rates may prompt redemptions from the Fund, which may force the Fund to sell investments at a time when it is not advantageous to do so, which could result in losses.</div> <div style="margin-top:4pt;">Issuer Risk. An issuer in which the Fund invests or to which it has exposure may perform poorly or below expectations, and the value of its securities may therefore decline, which may negatively affect the Fund’s performance. Underperformance of an issuer may be caused by poor management decisions, competitive pressures, breakthroughs in technology, reliance on suppliers, labor problems or shortages, corporate restructurings, fraudulent disclosures, natural disasters, military confrontations and actions, war, other conflicts, terrorism, disease/virus outbreaks, epidemics or other events, conditions and factors which may impair the value of your investment in the Fund.</div> <div style="margin-top:4pt;">Liquidity Risk. Liquidity risk is the risk associated with any event, circumstance, or characteristic of an investment or market that negatively impacts the Fund’s ability to sell, or realize the proceeds from the sale of, an investment at a desirable time or price. Liquidity risk may arise because of, for example, a lack of marketability of the investment, which means that when seeking to sell its portfolio investments, the Fund could find that selling is more difficult than anticipated, especially during times of high market volatility. Decreases in the number of financial institutions, including banks and broker-dealers, willing to make markets (match up sellers and buyers) in the Fund’s investments or decreases in their capacity or willingness to trade such investments may increase the Fund’s exposure to this risk. </div><div style="line-height:12.0pt;text-align:left;">The debt market has experienced considerable growth, and financial institutions making markets in instruments purchased and sold by the Fund (e.g., bond dealers) have been subject to increased regulation. The impact of that growth and regulation on the ability and willingness of financial institutions to engage in trading or “making a market” in such instruments remains unsettled. Certain types of investments, such as lower-rated securities or those that are purchased and sold in over-the-counter markets, may be especially subject to liquidity risk. Securities or other assets in which the Fund invests may be traded in the over-the-counter market rather than on an exchange and therefore may be more difficult to purchase or sell at a fair price, which may have a negative impact on the Fund’s performance. Market participants attempting to sell the same or a similar instrument at the same time as the Fund could exacerbate the Fund’s exposure to liquidity risk. The Fund may have to accept a lower selling price for the holding, sell other liquid or more liquid investments that it might otherwise prefer to hold (thereby increasing the proportion of the Fund’s investments in less liquid or illiquid securities), or forgo another more appealing investment opportunity. The liquidity of Fund investments may change significantly over time and certain investments that were liquid when purchased by the Fund may later become illiquid, particularly in times of overall economic distress. Changing regulatory, market or other conditions or environments (for example, the interest rate or credit environments) may also adversely affect the liquidity and the price of the Fund's investments. Judgment plays a larger role in valuing illiquid or less liquid investments as compared to valuing liquid or more liquid investments. Price volatility may be higher for illiquid or less liquid investments as a result of, for example, the relatively less frequent pricing of such securities (as compared to liquid or more liquid investments). Generally, the less liquid the market at the time the Fund sells a portfolio investment, the greater the risk of loss or decline of value to the Fund. Overall market liquidity and other factors can lead to an increase in redemptions, which may negatively impact Fund performance and NAV, including, for example, if the Fund is forced to sell investments in a down market.</div> <div style="margin-top:4pt;">Market Risk. The Fund may incur losses due to declines in the value of one or more securities in which it invests. These declines may be due to factors affecting a particular issuer, or the result of, among other things, political, regulatory, market, economic or social developments affecting the relevant market(s) more generally. In addition, turbulence in financial markets and reduced liquidity in equity, credit and/or fixed income markets may negatively affect many issuers, which could adversely affect the Fund’s ability to price or value hard-to-value assets in thinly traded and closed markets and could cause significant redemptions and operational challenges. Global economies and financial markets are increasingly interconnected, and conditions and events in one country, region or financial market may adversely impact issuers in a different country, region or financial market. These risks may be magnified if certain events or developments adversely interrupt the global supply chain; in these and other circumstances, such risks might affect companies worldwide. As a result, local, regional or global events such as terrorism, war, other conflicts, natural disasters, disease/virus outbreaks and epidemics or other public health issues, recessions, depressions or other events – or the potential for such events – could have a significant negative impact on global economic and market conditions.</div> <div style="margin-top:4pt;">Mortgage- and Other Asset-Backed Securities Risk. The value of any mortgage-backed and other asset-backed securities including collateralized debt obligations and collateralized loan obligations, if any, held by the Fund may be affected by, among other things, changes or perceived changes in: interest rates; factors concerning the interests in and structure of the issuer or the originator of the mortgages or other assets; the creditworthiness of the entities that provide any supporting letters of credit, surety bonds or other credit enhancements; or the market's assessment of the quality of underlying assets. Payment of principal and interest on some mortgage-backed securities (but not the market value of the securities themselves) may be guaranteed by the full faith and credit of a particular U.S. Government agency, authority, enterprise or instrumentality, and some, but not all, are also insured or guaranteed by the U.S. Government. Mortgage-backed securities issued by non-governmental issuers (such as commercial banks, savings and loan institutions, private mortgage insurance companies, mortgage bankers and other secondary market issuers) may entail greater risk than obligations guaranteed by the U.S. Government. Mortgage- and other asset-backed securities are subject to liquidity risk and prepayment risk. A decline or flattening of housing values may cause delinquencies in mortgages underlying mortgage-backed securities and thereby adversely affect the ability of the mortgage-backed securities issuer to make principal and/or interest payments to mortgage-backed securities holders, including the Fund. Rising or high interest rates tend to extend the duration of mortgage- and other asset-backed securities, making their prices more volatile and more sensitive to changes in interest rates.</div> <div style="line-height:12.0pt;text-align:left;">Prepayment and Extension Risk. Prepayment and extension risk is the risk that a bond or other security or investment might, in the case of prepayment risk, be called or otherwise converted, prepaid or redeemed before maturity and, in the case of extension risk, that the investment might not be called as expected. In the case of prepayment risk, if the investment is converted, prepaid or redeemed before maturity, the portfolio managers may not be able to invest the proceeds in other investments providing as high a level of income, resulting in a reduced yield to the Fund. As interest rates decrease or spreads narrow on such investments, the likelihood of prepayment increases. Conversely, extension risk is the risk that an unexpected rise in interest rates will extend the life of an investment beyond the prepayment time. If the Fund’s investments are locked in at a lower interest rate for a longer period of time, the portfolio managers may be unable to capitalize on investments with higher interest rates or wider spreads.</div> <div style="margin-top:4pt;">Reinvestment Risk. Reinvestment risk arises when the Fund is unable to reinvest income or principal at the same or at least the same return it is currently earning.</div> <div style="margin-top:4pt;">Rule 144A and Other Exempted Securities Risk. The Fund may invest in privately placed and other securities or instruments exempt from SEC registration (collectively “private placements”), subject to certain regulatory restrictions. In the U.S. market, private placements are typically sold only to qualified institutional buyers, or qualified purchasers, as applicable. An insufficient number of buyers interested in purchasing private placements at a particular time could adversely affect the marketability of such investments and the Fund might be unable to dispose of them promptly or at reasonable prices, subjecting the Fund to liquidity risk. The Fund’s holdings of private placements may increase the level of Fund illiquidity if eligible buyers are unable or unwilling to purchase them at a particular time. Issuers of Rule 144A eligible securities are required to furnish information to potential investors upon request. However, the required disclosure is much less extensive than that required of public companies and is not publicly available since the offering information is not filed with the SEC. Further, issuers of Rule 144A eligible securities can require recipients of the offering information (such as the Fund) to agree contractually to keep the information confidential, which could also adversely affect the Fund’s ability to dispose of the security.</div> <div style="margin-top:4pt;">Sovereign Debt Risk. The willingness or ability of a sovereign or quasi-sovereign debtor to repay principal and pay interest in a timely manner may be affected by a variety of factors, including its cash flow situation, the extent of its reserves, the availability of sufficient foreign exchange on the date a payment is due, the relative size of the debt service burden to the economy as a whole, the sovereign or quasi-sovereign debtor’s policy toward international lenders, and the political constraints to which such debtor may be subject.</div> <div style="margin-top:4pt;">U.S. Government Obligations Risk. While U.S. Treasury obligations are backed by the “full faith and credit” of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government.</div> <div style="margin-top:4pt;">Unrated Securities Risk. The Fund may purchase unrated securities which are not rated by a rating agency. Unrated securities may be less liquid than comparable rated securities and involve the risk that the Investment Manager may not accurately evaluate the security’s comparative credit rating. Analysis of creditworthiness of issuers of high yield securities may be more complex than for issuers of higher-quality debt securities. To the extent that the Fund purchases unrated securities, the Fund’s success in achieving its investment objective may depend more heavily on the Investment Manager’s creditworthiness analysis than if the Fund invested exclusively in rated securities.</div> Performance Information The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class A share performance (without sales charges) has varied for each full calendar year shown. If the sales charges were reflected, returns shown would be lower. The table below the bar chart compares the Fund’s returns (after applicable sales charges shown in the Shareholder Fees table in this prospectus) for the periods shown with a broad measure of market performance, as well as another measure of performance for markets in which the Fund may invest. <div style="margin-top:4pt;">The following bar chart and table show you how the Fund has performed in the past, and can help you understand the risks of investing in the Fund. The bar chart shows how the Fund’s Class A share performance (without sales charges) has varied for each full calendar year shown. If the sales charges were reflected, returns shown would be lower. The table below the bar chart compares the Fund’s returns (after applicable sales charges shown in the Shareholder Fees table in this prospectus) for the periods shown with a broad measure of market performance, as well as another measure of performance for markets in which the Fund may invest.</div><div style="line-height:12.0pt;text-align:left;">The performance of one or more share classes shown in the table below begins before the indicated inception date for such share class. The returns shown for each such share class include the returns of the Fund’s Class Inst shares (without applicable sales charges) for periods prior to its inception date.</div><div style="margin-top:4pt;">Except for differences in annual returns resulting from differences in expenses and sales charges (where applicable), the share classes of the Fund would have substantially similar annual returns because all share classes of the Fund invest in the same portfolio of securities.</div><div style="margin-top:4pt;">The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates in effect during the period indicated in the table and do not reflect the impact of state, local or foreign taxes. Your actual after-tax returns will depend on your personal tax situation and may differ from those shown in the table. In addition, the after-tax returns shown in the table do not apply to shares held in tax-advantaged accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes.</div><div style="margin-top:4pt;">The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedleus.com. </div> The bar chart shows how the Fund’s Class A share performance (without sales charges) has varied for each full calendar year shown. If the sales charges were reflected, returns shown would be lower. The table below the bar chart compares the Fund’s returns (after applicable sales charges shown in the Shareholder Fees table in this prospectus) for the periods shown with a broad measure of market performance, as well as another measure of performance for markets in which the Fund may invest. The after-tax returns shown in the Average Annual Total Returns table below are calculated using the highest historical individual U.S. federal marginal income tax rates in effect during the period indicated in the table and do not reflect the impact of state, local or foreign taxes. In addition, the after-tax returns shown in the table do not apply to shares held in tax-advantaged accounts such as 401(k) plans or Individual Retirement Accounts (IRAs). The after-tax returns are shown only for Class A shares and will vary for other share classes. The Fund’s past performance (before and after taxes) is no guarantee of how the Fund will perform in the future. 800.345.6611 columbiathreadneedleus.com Year by Year Total Return (%)as of December 31 Each Year* Best 2020-06-30 0.0640 Worst 2020-03-31 -0.0574 Year to Date return 2026-06-30 0.0127 Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2025) 1992-10-02 1992-10-02 1992-10-02 0.0459 0.0253 0.0234 0.0270 0.0121 0.0133 0.0269 0.0136 0.0135 1992-10-02 0.0409 0.0219 0.0186 1992-09-30 0.0593 0.0299 0.0270 2012-11-08 0.0600 0.0307 0.0277 2009-07-15 0.0601 0.0311 0.0283 2024-10-02 0.0593 0.0299 0.0270 0.0535 0.0197 0.0209 0.0730 -0.0036 0.0201 Year to Date return as of June 30, 2026: 1.27% “Total annual Fund operating expenses” include acquired fund fees and expenses (expenses the Fund incurs indirectly through its investments in other investment companies) and may be higher than the ratio of expenses to average net assets shown in the Financial Highlights section of this prospectus because the ratio of expenses to average net assets does not include acquired fund fees and expenses. Columbia Management Investment Advisers, LLC and certain of its affiliates have contractually agreed to waive fees and/or to reimburse expenses (excluding transaction costs and certain other investment related expenses, interest, taxes, acquired fund fees and expenses, and infrequent and/or unusual expenses) through July 31, 2027, unless sooner terminated at the sole discretion of the Fund’s Board of Trustees (the Board). Under this agreement, the Fund’s net operating expenses, subject to applicable exclusions, will not exceed the annual rates of 0.71% for Class A, 1.26% for Class C, 0.46% for Class Inst, 0.39% for Class Inst2, 0.38% for Class Inst3 and 0.46% for Class S . Any differences in these annual rates relative to the annual rates noted in the last row of the above table (e.g., net expense ratios) are due to applicable exclusions under the agreement. The fee waivers and/or expense reimbursements shown in the table for Class Inst2 also reflect the contractual agreement of the Fund’s transfer agent to waive fees and/or to reimburse expenses through July 31, 2027, unless sooner terminated at the sole discretion of the Fund’s Board, so that the Fund’s transfer agency fees do not exceed the annual rate of 0.01% for Class Inst2. This charge is imposed on certain investments of between $1 million and $50 million redeemed within 18 months after purchase, as follows: 1.00% if redeemed within 12 months after purchase, and 0.50% if redeemed more than 12, but less than 18, months after purchase, with certain limited exceptions. This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.