Columbia
  Acorn European Fund^SM

As with all mutual funds, the Securities and Exchange Commission (SEC) has not approved or disapproved these securities or passed upon the adequacy of this prospectus. Any representation to the contrary is a criminal offense.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Adv	Class C	Class Inst	Class Inst2	Class Inst3
Management fees	1.14%	1.14%	1.14%	1.14%	1.14%	1.14%
Distribution and/or service (12b-1) fees	0.25%	0.00%	1.00%	0.00%	0.00%	0.00%
Other expenses	0.40%	0.40%	0.40%	0.40%	0.35%	0.31%
Total annual Fund operating expenses	1.79%	1.54%	2.54%	1.54%	1.49%	1.45%
Fee waivers and/or expense reimbursements(c)	(0.34%)	(0.34%)	(0.34%)	(0.34%)	(0.35%)	(0.34%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.45%	1.20%	2.20%	1.20%	1.14%	1.11%

(c)

Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to waive fees and reimburse certain expenses of the Fund, through April 30, 2024, so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings and expenses associated with the Fund’s investment in other investment companies, if any) do not exceed the annual rates of 1.45% for Class A shares, 1.20% for Class Adv shares, 2.20% for Class C shares, 1.20% for Class Inst shares, 1.14% for Class Inst2 shares and 1.11% for Class Inst3 shares. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager. The fee waivers and/or expense reimbursements shown in the table also reflect the contractual agreement of the Fund’s transfer agent, Columbia Management Investment Services Corp. (the Transfer Agent), to waive a portion of its fees through April 30, 2024, such that the Fund’s transfer agency fees do not exceed the annual rate of 0.05% of the average daily net assets of Class Inst2 shares. This arrangement may be terminated at the sole discretion of the Fund’s Board of Trustees.

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	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$714	$1,075	$1,459	$2,533
Class Adv (whether or not shares are redeemed)	$122	$453	$807	$1,806
Class C (assuming redemption of all shares at the end of the period)	$323	$758	$1,320	$2,666
Class C (assuming no redemption of shares)	$223	$758	$1,320	$2,666
Class Inst (whether or not shares are redeemed)	$122	$453	$807	$1,806
Class Inst2 (whether or not shares are redeemed)	$116	$437	$780	$1,750
Class Inst3 (whether or not shares are redeemed)	$113	$425	$760	$1,706

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Europe. The Fund is particularly susceptible to risks related to economic, political, regulatory or other events or conditions, including acts of war or other conflicts in the region, affecting issuers and countries in Europe. Countries in Europe are often closely connected and interdependent, and events in one European country can have an adverse impact on, and potentially spread to, other European countries. In addition, significant private or public debt problems in a single European Union (EU) country can pose economic risks to the EU as a whole. As a result, the Fund’s NAV may be more volatile than the NAV of a more geographically diversified fund. If securities of issuers in Europe fall out of favor, it may cause the Fund to underperform other funds that do not focus their investments in this region of the world. Any uncertainty caused by the departure of the United Kingdom (UK) from the EU, which occurred in January 2020, could have negative impacts on the UK and EU, as well as other European economies

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and the broader global economy. These could include negative impacts on currencies and financial markets as well as increased volatility and illiquidity, and potentially lower economic growth in markets in Europe, which could adversely affect the value of your investment in the Fund.

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Industrials Sector. The Fund is more susceptible to the particular risks that may affect companies in the industrials sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the industrials sector are subject to certain risks, including changes in supply and demand for their specific product or service and for industrial sector products in general, including decline in demand for such products due to rapid technological developments and frequent new product introduction. Performance of such companies may be affected by factors including government regulation, world events, economic conditions and risks for environmental damage and product liability claims.

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Information Technology Sector. The Fund is more susceptible to the particular risks that may affect companies in the information technology sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the information technology sector are subject to certain risks, including the risk that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. Performance of such companies may be affected by factors including obtaining and protecting patents (or the failure to do so) and significant competitive pressures, including aggressive pricing of their products or services, new market entrants, competition for market share and short product cycles due to an accelerated rate of technological developments. Such competitive pressures may lead to limited earnings and/or falling profit margins. As a result, the value of their securities may fall or fail to rise. In addition, many information technology sector companies have limited operating histories and prices of these companies’ securities historically have been more volatile than other securities, especially over the short term. Some companies in the information technology sector are facing increased government and regulatory scrutiny and may be subject to adverse government or regulatory action, which could negatively impact the value of their securities.

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Health Care Sector. The Fund is more susceptible to the particular risks that may affect companies in the health care sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the health care sector are subject to certain risks, including restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, and the rising cost of medical products and services (especially for companies dependent upon a relatively limited number of products or services), among others. Performance of such companies may be affected by factors including government regulation, obtaining and protecting patents (or the failure to do so), product liability and other similar litigation as well as product obsolescence.

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Year by Year Total Return (%) as of December 31 Each Year*	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart
	Best	2nd Quarter 2020	30.55%
	Worst	1st Quarter 2020	-28.33%

*	Year to Date return as of March 31, 2023: 12.71%

	Share Class Inception Date	1 Year	5 Years	10 Years
Class Inst	08/19/2011
returns before taxes		-38.02%	2.05%	6.72%
returns after taxes on distributions		-37.93%	2.02%	6.63%
returns after taxes on distributions and sale of Fund shares		-22.42%	1.68%	5.53%
Class A returns before taxes	08/19/2011	-41.71%	0.60%	5.82%
Class Adv returns before taxes	06/25/2014	-38.03%	2.05%	6.73%
Class C returns before taxes	08/19/2011	-39.25%	1.04%	5.66%
Class Inst2 returns before taxes	11/08/2012	-37.97%	2.13%	6.77%
Class Inst3 returns before taxes	03/01/2017	-37.96%	2.14%	6.77%
MSCI AC Europe Small Cap Index (Net) (reflects reinvested dividends net of withholding taxes but reflects no deductions for fees, expenses or other taxes)		-26.59%	-0.18%	6.48%

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Online		Regular Mail		Express Mail		By Telephone
columbiathreadneedleus.com/investor/		Columbia Management Investment Services Corp. P.O. Box 219104 Kansas City, MO 64121-9104		Columbia Management Investment Services Corp. c/o SS&C GIDS, Inc. 430 W 7th Street, Suite 219104 Kansas City, MO 64105-1407		800.422.3737

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Investment Objective

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations generally in the range of market capitalizations in the MSCI AC Europe Small Cap Index (Net), the Fund's benchmark, (the Index) at the time of purchase (between $128.6 million and $8.4 billion as of March 31, 2023). The market capitalization range and composition of companies in the Index are subject to change. As such, the size of the companies in which the Fund invests may change. The Fund determines a company’s market capitalization at the time of investment. As long as a majority of its net assets are invested in companies within the market capitalization range of the Index, the Fund may continue to hold and make new investments in a security even if the company’s market capitalization grows beyond the market capitalization of the largest company within the range of the Index or falls below the market capitalization of the smallest company within the Index. The Investment Manager from time to time emphasizes one or more sectors in selecting the Fund’s investments, including the industrials, information technology, and health care sectors.

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Small- and Mid-Cap Company Securities Risk. Securities of small- and mid-cap companies can, in certain circumstances, have a higher potential for gains than securities of larger, more established companies but may also have more risk. For example, small- and mid-cap companies may be more vulnerable to market downturns and adverse business or economic events than larger companies because they may have more limited financial resources and business operations. Small- and mid-cap companies are also more likely than larger companies to have more limited product lines and operating histories and to depend on smaller and generally less experienced management teams. Securities of small- and mid-cap companies may trade less frequently and in smaller volumes and may be less liquid and fluctuate more sharply in value than securities of larger companies. When the Fund takes significant positions in small- and mid-cap companies with limited trading volumes, the liquidation of those positions, particularly in a distressed market, could be prolonged and result in Fund investment losses that would affect the value of your investment in the Fund. In addition, some small- and mid-cap companies may not be widely followed by the investment community, which can lower the demand for their stocks.

Geographic Focus Risk. The Fund may be particularly susceptible to risks related to economic, political, regulatory or other events or conditions affecting issuers and countries within the specific geographic regions in which the Fund invests. Currency devaluations could occur in countries that have not yet experienced currency devaluation to date, or could continue to occur in countries that have already experienced such devaluations. As a result, the Fund’s NAV may be more volatile than the NAV of a more geographically diversified fund.

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Europe. The Fund is particularly susceptible to risks related to economic, political, regulatory or other events or conditions, including acts of war or other conflicts in the region, affecting issuers and countries in Europe. Countries in Europe are often closely connected and interdependent, and events in one European country can have an adverse impact on, and potentially spread to, other European countries. Most developed countries in Western Europe are members of the EU, and many are also members of the European Economic and Monetary Union (EMU). European countries can be significantly affected by the tight fiscal and monetary controls that the EMU imposes on its members and with which candidates for EMU membership are required to comply. In addition, significant private or public debt problems in a single EU country can pose economic risks to the EU as a whole. Unemployment in Europe has historically been higher than in the United States and public deficits are an ongoing concern in many European countries. As a result, the Fund’s NAV may be more volatile than the NAV of a more geographically diversified fund. If securities of issuers in Europe fall out of favor, it may cause the Fund to underperform other funds that do not focus their investments in this region of the world. Any uncertainty caused by the departure of the UK from the EU, which occurred in January 2020, could have negative impacts on the UK and EU, as well as other European economies and the broader global economy. These could include negative impacts on currencies and financial markets as well as increased volatility and illiquidity, and potentially lower economic growth in markets in the UK, Europe and globally, which could adversely affect the value of your investment in the Fund. Any attempt by the Fund to hedge against or otherwise protect its portfolio or to profit from such circumstances may fail and, accordingly, an investment in the Fund could lose money over short or long periods.

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The large-scale invasion of Ukraine by Russia in February 2022 has resulted in sanctions and market disruptions, including declines in regional and global stock markets, unusual volatility in global commodity markets and significant devaluations of Russian currency. The extent and duration of the military action are impossible to predict but could be significant. Market disruption caused by the Russian military action, and any counter measures or responses thereto (including international sanctions, a downgrade in a country’s credit rating, purchasing and financing restrictions, boycotts, tariffs, changes in consumer or purchaser preferences, cyberattacks and espionage) could have severe adverse impacts on regional and/or global securities and commodities markets, including markets for oil and natural gas. These impacts may include reduced market liquidity, distress in credit markets, further disruption of global supply chains, increased risk of inflation, and limited access to investments in certain international markets and/or issuers. These developments and other related events could negatively impact Fund performance.

Focused Portfolio Risk. The Fund, because it may invest in a limited number of companies, may have more volatility in its NAV and is considered to have more risk than a fund that invests in a greater number of companies because changes in the value of a single security may have a more significant effect, either negative or positive, on the Fund’s NAV. To the extent the Fund invests its assets in fewer securities, the Fund is subject to greater risk of loss if any of those securities decline in price.

Growth Securities Risk. Growth securities typically trade at a higher multiple of earnings than other types of equity securities. Accordingly, the market values of growth securities may never reach their expected market value and may decline in price. In addition, growth securities, at times, may not perform as well as value securities or the stock market in general, and may be out of favor with investors for varying periods of time. Growth securities may also be sensitive to movements in interest rates.

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Operational and Settlement Risks of Foreign Securities. The Fund’s foreign securities are generally held outside the United States in the primary market for the securities in the custody of certain eligible foreign banks and trust companies (foreign sub-custodians), as permitted under the Investment Company Act of 1940 (the 1940 Act). Settlement practices for foreign securities may differ from those in the United States. Some countries have limited governmental oversight and regulation of industry practices, stock exchanges, depositories, registrars, brokers and listed companies, which increases the risk of corruption and fraud and the possibility of losses to the Fund. In particular, under certain circumstances, foreign securities may settle on a delayed delivery basis, meaning that the Fund may be required to make payment for securities before the Fund has actually received delivery of the securities or deliver securities prior to the receipt of payment. Typically, in these cases, the Fund will receive evidence of ownership in accordance with the generally accepted settlement practices in the local market entitling the Fund to delivery or payment at a future date, but there is a risk that the security will not be delivered to the Fund or that payment will not be received, although the Fund and its foreign sub-custodians take reasonable precautions to mitigate this risk. Losses can also result from lost, stolen or counterfeit securities; defaults by brokers and banks; failures or defects of the settlement system; or poor and improper record keeping by registrars and issuers.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in an industry or related group of industries within one or more economic sectors , including the industrials, information technology, and health care sectors. Companies in the same sector may be similarly affected

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by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that industry or group of industries or economic sector than funds that invest more broadly. Generally, the more broadly the Fund invests, the more it spreads risk and potentially reduces the risks of loss and volatility.

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Industrials Sector. The Fund is more susceptible to the particular risks that may affect companies in the industrials sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the industrials sector are subject to certain risks, including changes in supply and demand for their specific product or service and for industrial sector products in general, including decline in demand for such products due to rapid technological developments and frequent new product introduction. Performance of such companies may be affected by factors including government regulation, world events, economic conditions and risks for environmental damage and product liability claims.

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Information Technology Sector. The Fund is more susceptible to the particular risks that may affect companies in the information technology sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the information technology sector are subject to certain risks, including the risk that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. Performance of such companies may be affected by factors including obtaining and protecting patents (or the failure to do so) and significant competitive pressures, including aggressive pricing of their products or services, new market entrants, competition for market share and short product cycles due to an accelerated rate of technological developments. Such competitive pressures may lead to limited earnings and/or falling profit margins. As a result, the value of their securities may fall or fail to rise. In addition, many information technology sector companies have limited operating histories and prices of these companies’ securities historically have been more volatile than other securities, especially over the short term. Some companies in the information technology sector are facing increased government and regulatory scrutiny and may be subject to adverse government or regulatory action, which could negatively impact the value of their securities.

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Health Care Sector. The Fund is more susceptible to the particular risks that may affect companies in the health care sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the health care sector are subject to certain risks, including restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, and the rising cost of medical products and services (especially for companies dependent upon a relatively limited number of products or services), among others. Performance of such companies may be affected by factors including government regulation, obtaining and protecting patents (or the failure to do so), product liability and other similar litigation as well as product obsolescence.

Issuer Risk. An issuer in which the Fund invests may perform poorly, 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 and epidemics or other events, conditions and factors.

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This section describes certain investment strategies and policies that the Fund may utilize in pursuit of its investment objective and some additional factors and risks involved with investing in the Fund. For information about risks associated with changing levels of Fund distributions, see the Fund’s SAI.

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The Fund’s investment objective and non-fundamental investment policies (including its principal and additional investment strategies) can be changed by the Board without shareholder approval, but may require notice to shareholders in certain instances. The Fund’s fundamental investment policies, as identified in the SAI, may be changed only with Board and shareholder approval in accordance with the voting requirements of the 1940 Act. For additional information about changing the Fund’s fundamental and non-fundamental investment policies, see the SAI.

The Fund may enter into derivative transactions or otherwise have exposure to derivative transactions through underlying investments. The Fund expects to enter into such transactions primarily in the form of stock index futures in order to obtain exposure to the overall sector of the market represented by a particular stock index or to invest the Fund’s uninvested cash balances in a manner that the Investment Manager believes aligns more closely with the Fund’s investment strategy than simply holding short-term fixed income investments or cash equivalents (known as cash equitization). Derivatives are financial contracts whose values are, for example, based on (or “derived” from) traditional securities (such as a stock or bond), assets (such as a commodity like gold or a foreign currency), reference rates (such as the Secured Overnight Financing Rate (commonly known as SOFR)) or market indices (such as the Standard & Poor’s 500® Index). The use of derivatives is a highly specialized activity which involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. Derivatives involve special risks and may result in losses or may limit the Fund’s potential gain from favorable market movements. Derivative strategies typically expose the Fund to gains and losses in excess of the amount actually invested in the derivative. This characteristic of a derivative (known as "leverage") may exaggerate a loss, potentially causing the Fund to lose more money than it would have lost had it invested in the underlying security or other asset directly. The values of derivatives may move in unexpected ways, especially in unusual (including distressed) market conditions, and may result in increased volatility in the value of the derivative and/or the Fund’s shares, among other consequences.  The use of derivatives may also increase the amount of taxes payable by shareholders holding shares in a taxable account. Other risks arise from the Fund’s potential inability to terminate or to sell derivative positions. A liquid secondary market may not always exist for the Fund’s derivative positions at times when the Fund might wish to terminate or to sell such positions. Over-the-counter instruments (investments not traded on an exchange) may be illiquid, and transactions in derivatives traded in the over-the-counter market are subject to the risk that the other party will not meet its obligations. The use of derivatives also involves the risks of mispricing or improper valuation and that changes in the value of the derivative may not correlate perfectly with the underlying security, asset, reference rate or index. The Fund also may not be able to find a suitable derivative transaction counterparty, and thus may be unable to engage in derivative transactions when it is deemed favorable to do so, or at all. U.S. federal legislation has been enacted that provides for new clearing, margin, reporting and registration requirements for participants in the derivatives market. These changes could restrict and/or impose significant costs or other burdens upon the Fund’s participation in derivatives transactions. The U.S. government and the European Union (and some other jurisdictions) have enacted regulations and similar requirements that prescribe clearing, margin, reporting and registration requirements for participants in the derivatives market. These requirements are

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evolving and their ultimate impact on the Fund remains unclear, but such impact could include restricting and/or imposing significant costs or other burdens upon the Fund’s participation in derivatives transactions. Additionally, in August 2022, regulations governing the use of derivatives by registered investment companies, such as the Fund, became effective. Rule 18f-4 under the 1940 Act, among other things, requires a fund that invests in derivative instruments beyond a specified limited amount to apply a value-at-risk-based limit to its portfolio and establish a comprehensive derivatives risk management program. As of the date of this prospectus, the Fund is not required to maintain a comprehensive derivatives risk management program under Rule 18f-4 given its more limited use of derivatives. For more information on the risks of derivative investments and strategies, see the SAI.

LIBOR Phase-Out Risk. Many derivatives and other financial instruments utilize or are permitted to utilize a floating interest rate based on the London Inter-bank Offered Rate (commonly known as LIBOR). On July 27, 2017, the United Kingdom’s Financial Conduct Authority (FCA) announced its intention to phase out the use of LIBOR by the end of 2021. The FCA and the ICE Benchmark Administration have since announced that a majority of U.S. dollar LIBOR settings will cease publication after June 30, 2023. A subset of non-U.S. dollar LIBOR settings is continuing to be published on a “synthetic” basis and it is possible that a subset of U.S. dollar LIBOR settings will also be published after June 30, 2023 on a “synthetic” basis. Any such publications are, or would be considered, non-representative of the underlying market. Uncertainty related to the liquidity impact of changes in reference rates, and how to appropriately adjust these rates at the time of transition, poses risks for the Fund. It is difficult to predict the full impact of the transition away from LIBOR on the Fund until new reference rates and fallbacks for both legacy and new products, instruments and contracts are commercially accepted and market practices become more settled. The Investment Manager monitors the Fund’s LIBOR exposure risks, including the extent to which any derivative and/or debt investments allow for the utilization of alternative rate(s), such as the SOFR, which the U.S. Federal Reserve is promoting as the alternative reference rate to LIBOR.

The Investment Manager and its affiliate, Columbia Management Investment Advisers, LLC (Columbia Management), serve as investment advisers to mutual funds and ETFs using the Columbia brand (Columbia Funds), including mutual funds that are structured as “fund-of-funds”, and provides asset-allocation services to (i) shareholders by investing in shares of other Columbia Funds, which may include the Fund (collectively referred to in this section as Underlying Funds), and (ii) discretionary managed accounts (collectively referred to as affiliated products) that invest exclusively in Underlying Funds. These affiliated products, individually or collectively, may own a significant percentage of the outstanding shares of one or more Underlying Funds, and the Investment Manager and Columbia Management seek to balance potential conflicts of interest between the affiliated products and the Underlying Funds in which they invest. The affiliated products’ investment in the Underlying Funds may have the effect of creating economies of scale, possibly resulting in lower expense ratios for the Underlying Funds, because the affiliated products may own substantial portions of the shares of Underlying Funds. However, redemption of Underlying Fund shares by one or more affiliated products could cause the expense ratio of the Underlying Fund to increase, as its fixed costs would be spread over a smaller asset base. Because of large positions of certain affiliated products, the Underlying Funds may experience relatively large inflows and outflows of cash due to affiliated products’ purchases and sales of Underlying Fund shares. Although the Investment Manager or Columbia Management may seek to minimize the impact of these transactions where possible, for example, by structuring them over a reasonable period of time or through other measures, Underlying Funds may experience increased expenses as they buy and sell portfolio securities to manage the cash flow effect related to these transactions. Further, when the Investment Manager or Columbia Management structures transactions over a reasonable period of time in order to manage the potential impact of the buy and sell decisions for the affiliated products, those affiliated products, including funds-of-funds, may pay more or less (for purchase activity), or receive more or less (for redemption activity), for shares of the Underlying Funds than if the transactions were executed in one transaction. In addition, substantial redemptions by affiliated products within a short period of time could require the Underlying Fund to liquidate positions more rapidly than would otherwise be desirable, which may have the effect of reducing or eliminating potential gain or causing it to realize a loss. In order to meet such redemptions, the Underlying Fund may be forced to sell its liquid (or more liquid) positions, leaving the Underlying Fund holding, post-redemption, a relatively larger position in illiquid investments (i.e., any investment that the Fund reasonably expects cannot be sold or disposed of in current market conditions in seven calendar days or

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The Fund may from time to time take temporary defensive investment positions that are inconsistent with the Fund’s principal investment strategies in attempting to respond to adverse market, economic, political, social or other conditions. These investment positions may include, without limitation, investing some or all of its assets in money market instruments or shares of affiliated or unaffiliated money market funds or holding some or all of its assets in cash or cash equivalents. The Fund may take such defensive investment positions for as long a period as the Investment Manager deems necessary. During these times, the Investment Manager may make frequent portfolio changes, which could result in increased trading expenses and taxes, and decreased Fund performance.

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Benchmarks are indices that provide some comparative guidance in assessing the Fund’s performance. The Investment Manager selects the benchmark(s) it believes provide meaningful comparisons for the Fund. However, there may be different or additional indices that more closely reflect the market sectors in which the Fund invests. The Fund’s benchmark(s) may change from time to time. The benchmark included in this prospectus is intended only as a guidepost for your assessment of the Fund’s performance.

Portfolio Holdings Versus the Benchmarks

The Fund does not limit its investments to the securities within its benchmarks, and accordingly the Fund's holdings may diverge significantly from those of the benchmarks selected by the Investment Manager. In addition, the Fund may invest in securities outside the industry and geographic sectors represented in its benchmarks. The Fund's weightings in individual securities, and in industry and geographic sectors, may also vary considerably from those of its benchmarks.

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Other Expenses

“Other expenses” consist of the fees the Fund pays to its administrator, custodian, transfer agent, auditors, lawyers and trustees, costs relating to compliance and miscellaneous expenses. Generally, these expenses are allocated on a pro rata basis across all share classes. These expenses include certain sub-transfer agency and shareholder servicing fees. Transfer agency fees and certain shareholder servicing fees, however, are class specific. They differ by share class because the shareholder services provided to each share class may be different. Accordingly, the differences in “other expenses” among share classes are primarily the result of the different transfer agency and shareholder servicing fees applicable to each share class. For more information on these fees, see Choosing a Share Class — Financial Intermediary Compensation.

The Investment Manager has contractually agreed to waive fees and reimburse certain expenses of the Fund through April 30, 2024, so that ordinary operating expenses (excluding transaction costs and certain other investment-related expenses, interest and fees on borrowings, and expenses associated with the Fund’s investment in other investment companies, if any) do not exceed the annual rates of:

This arrangement may only be amended or terminated with approval from the Board and the Investment Manager.

The fee waivers and/or expense reimbursements shown in the table above also reflect the contractual agreement of the Fund's Transfer Agent to waive a portion of its fees through April 30, 2024, such that the Fund's transfer agency fees do not exceed the annual rate of 0.05% of the average daily net assets of Class Inst2 shares. This arrangement may be terminated at the sole discretion of the Board.

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Columbia Wanger Asset Management, LLC is located at 71 S. Wacker Drive, Suite 2500, Chicago, Illinois 60606. As of March 31, 2023, the Investment Manager had assets under management of approximately $6.8 billion. The Investment Manager is a registered investment adviser and wholly-owned subsidiary of Columbia Management, which is a wholly-owned subsidiary of Ameriprise Financial. In addition to serving as an investment adviser to mutual funds, the Investment Manager acts as an investment manager for other private funds and institutional accounts.

The Fund pays the Investment Manager a fee for its investment advisory services. The fee is calculated as a percentage of the daily net assets of the Fund and is paid monthly. For the Fund’s most recent fiscal year, aggregate fees paid to the Investment Manager by the Fund amounted to 1.14% of average daily net assets of the Fund, before any applicable reimbursements.

A discussion regarding the basis for the Board’s approval of the renewal of the Fund’s investment management services agreement with the Investment Manager is available in the Fund’s semiannual report to shareholders for the fiscal period ended June 30, 2022.

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Pursuant to some of these arrangements or relationships, certain personnel of Columbia Management and other Affiliates may serve as “associated persons” or officers of the Investment Manager and, in this capacity, subject to the oversight and supervision of the Investment Manager and consistent with the investment objectives, policies and limitations set forth in this prospectus and the Fund's SAI, and with the Investment Manager’s and the Fund's compliance policies and procedures, may provide such services to the Fund.

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Columbia Management Investment Services Corp. is a registered transfer agent and wholly-owned subsidiary of Ameriprise Financial. The Transfer Agent is located at 290 Congress Street, Boston, MA 02210, and its responsibilities include processing purchases, redemptions and exchanges of Fund shares, calculating and paying distributions, maintaining shareholder records, preparing account statements and providing customer service. The Transfer Agent has engaged SS&C GIDS, Inc. to provide various shareholder or “sub-transfer agency” services. In addition, the Transfer Agent enters into agreements with various financial intermediaries through which you may hold Fund shares, pursuant to which the Transfer Agent pays these financial intermediaries for providing certain shareholder services. Depending on the type of account, the Fund pays the Transfer Agent a per account fee for each open account and compensates the Transfer Agent for certain out-of-pocket expenses, including certain payments to financial intermediaries through which shares are held. In addition, subject to certain limitations, the Fund compensates the Transfer Agent for payments made to financial intermediaries for the shareholder services that the intermediaries provide, in amounts that vary by share class and with the type of intermediary and the type of shareholder services provided. The Transfer Agent is contractually obligated to oversee such intermediaries for the purpose of reasonably assuring their compliance with applicable law and the terms of their agreements to provide the shareholder services. For more information about Shareholder Services fees, see Choosing a Share Class — Financial Intermediary Compensation.

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Ameriprise Financial and certain of its affiliates are involved in the normal course of business in legal proceedings which include regulatory inquiries, arbitration and litigation, including class actions concerning matters arising in connection with the conduct of their activities as part of a diversified financial services firm. Ameriprise Financial believes that the Fund is not currently the subject of, and that neither Ameriprise Financial nor any of its affiliates are the subject of, any pending legal, arbitration or regulatory proceedings that are likely to have a material adverse effect on the Fund or the ability of Ameriprise Financial or its affiliates to perform under their contracts with the Fund. Information regarding certain pending and settled legal proceedings may be found in the Fund’s shareholder reports and in the SAI. Additionally, Ameriprise Financial is required to make quarterly (10-Q), annual (10-K) and, as necessary, 8-K filings with the SEC on legal and regulatory matters that relate to Ameriprise Financial and its affiliates. Copies of these filings may be obtained by accessing the SEC website at sec.gov.

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The Funds

Additional information about the Funds, including sales charges and other class features and policies, can be obtained, free of charge, at columbiathreadneedleus.com,* by calling toll-free 800.345.6611, or by writing (regular mail) to Columbia Management Investment Services Corp., P.O. Box 219104, Kansas City, MO 64121-9104 or (express mail) Columbia Management Investment Services Corp., c/o SS&C GIDS, Inc., 430 W 7^th Street, Ste 219104, Kansas City, MO 64105-1407.

*	The website references in this prospectus are inactive links and information contained in or otherwise accessible through the referenced websites does not form a part of this prospectus.

Financial Intermediaries

The term “financial intermediary” refers to the selling and servicing agents that are authorized to sell and/or service shares of the Funds. Financial intermediaries include broker-dealers and financial advisors as well as firms that employ broker-dealers and financial advisors, including, for example, brokerage firms, banks, investment advisers, third party administrators and other firms in the financial services industry.

Omnibus Accounts

The term “omnibus account” refers to a financial intermediary’s account with the Fund (held directly through the Transfer Agent) that represents the combined holdings of, and transactions in, Fund shares of one or more clients of the financial intermediary (beneficial Fund shareholders). Omnibus accounts are held in the name of the financial intermediaries and not in the name of the beneficial Fund shareholders invested in the Fund through omnibus accounts.

Retirement Plans and Omnibus Retirement Plans

The term “retirement plan” refers to retirement plans created under Sections 401(a), 401(k), 457 and 403(b) of the Internal Revenue Code of 1986, as amended (the Code), and non-qualified deferred compensation plans governed by Section 409A of the Code and similar plans, but does not refer to individual retirement plans, such as traditional IRAs and Roth IRAs. The term “omnibus retirement plan” refers to a retirement plan that has a plan-level or omnibus account with the Transfer Agent.

Networked Accounts

Networking, offered by the Depository Trust & Clearing Corporation’s Wealth Management Services (WMS), is the industry standard IT system for mutual fund account reconciliation and dividend processing.

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Front-End Sales Charge Calculation

The front-end sales charge is calculated as a percentage of the offering price.

The dollar amount of any applicable front-end sales charge is the difference between the offering price of the shares you buy and the NAV of those shares. To determine the front-end sales charge you will pay when you buy Class A shares, the Fund will add the amount of your investment to the value of your account (and any other accounts eligible for aggregation of which you or your financial intermediary notifies the Fund) and base the sales charge on the aggregate amount. For information on account value aggregation, sales charge waivers and other important information, see Choosing a Share Class — Reductions/Waivers of Sales Charges.

Contingent Deferred Sales Charge

A contingent deferred sales charge (CDSC) is a sales charge applied at the time you sell your shares, unlike a front-end sales charge that is applied at the time of purchase. A CDSC can vary based on the length of time that you have held your shares. A CDSC is applied to the NAV at the time of your purchase or sale, whichever is lower, and will not be applied to any shares you receive through Fund distribution reinvestments or any amount that represents appreciation in the value of your shares. For purposes of calculating a CDSC, the start of the holding period is generally the first day of the month in which your purchase was made.

When you place an order to sell shares of a class that has a CDSC, the Fund will first redeem any shares that are not subject to a CDSC, followed by those you have held the longest. This means that if a CDSC is imposed, you cannot designate the individual shares being redeemed for U.S. federal income tax purposes. You should consult your tax advisor about the tax consequences of investing in the Fund. In certain circumstances, the CDSC may not apply. See Choosing a Share Class — Reductions/Waivers of Sales Charges for details.

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As described in more detail below, Class A shares have a front-end sales charge, which is deducted from your purchase price when you buy your shares, and results in a smaller dollar amount being invested in the Fund than the purchase price you pay (unless you qualify for a waiver or reduction of the sales charge). The Fund’s other share classes do not have a front-end sales charge, so the full amount of your purchase price is invested in those classes. Class A shares have lower ongoing distribution and/or service fees than Class C and Class R shares of the Fund. Over time, Class C and Class R shares can incur distribution and/or service fees that are equal to or more than the front-end sales charge and the distribution and/or service fees you would pay for Class A shares. Although the full amount of your purchase price of Class C and Class R shares is invested in a Fund, your return on this money will be reduced by the expected higher annual expenses of Class C and Class R shares. In this regard, note that effective April 1, 2021, Class C shares generally automatically convert to Class A shares of the same Fund in the month of or the month following the 8-year anniversary of the Class C shares purchase date (prior to April 1, 2021, the 10-year anniversary of such date). The Fund may convert Class C shares held through a financial intermediary to Class A shares sooner in connection with the withdrawal of Class C shares of the Fund from the financial intermediary’s platform or accounts. No sales charge or other charges will apply in connection with such conversions, and the conversions are free from U.S. federal income tax. Once your Class C shares convert to Class A shares, your total returns from an investment in the Fund may increase as a result of the lower operating costs of Class A shares. Class Adv, Class Inst, Class Inst2 and Class Inst3 shares of the Fund do not have distribution and/or service fees.

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The Distributor may also pay your financial intermediary a cumulative commission when you buy Class A shares in amounts not subject to a front-end sales charge, according to the following schedules (assets initially purchased into Class A shares of Columbia Government Money Market Fund, Columbia Large Cap Enhanced Core Fund, Columbia Large Cap Index Fund, Columbia Mid Cap Index Fund, Columbia Small Cap Index Fund, Columbia Ultra Short Duration Municipal Bond Fund, Columbia Ultra Short Term Bond Fund and Columbia U.S. Treasury Index Fund that were purchased without the application of a front-end sales charge are excluded for purposes of calculating a financial intermediary’s commission under these schedules):

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Your “Immediate Family” and Account Value Aggregation

For purposes of obtaining a breakpoint discount for Class A shares, the value of your account will be deemed to include the value of all applicable shares in eligible Fund accounts that are held by you and your “immediate family,” which includes your spouse, domestic partner, parent, step-parent, legal guardian, child under 21, step-child under 21, father-in-law and mother-in-law, provided that you and your immediate family members share the same mailing address. Any Fund accounts linked together for account value aggregation purposes as of the close of business on September 3, 2010 will be permitted to remain linked together. Group retirement plan accounts are valued at the retirement plan level.

The following accounts are eligible for account value aggregation as described above, provided that they are invested in Class A (excluding, in the case of Direct-at-Fund Accounts, Funds that do not assess a front-end sales charge, including Columbia Government Money Market Fund, Columbia Large Cap Enhanced Core Fund, Columbia Large Cap Index Fund, Columbia Mid Cap Index Fund, Columbia Small Cap Index Fund, Columbia Ultra Short Duration Municipal Bond Fund, Columbia Ultra Short Term Bond Fund and Columbia U.S. Treasury Index Fund, unless such shares were purchased via an exchange from Class A shares of a Fund on which you paid the Class A share applicable front-end sales charge), Class C, Class E, Class Inst or Class V shares of a Fund, or non-retirement plan accounts invested in Class Adv, Class Inst2 or Class Inst3 shares of a Fund: individual or joint accounts; Roth and traditional Individual Retirement Accounts (IRAs); Simplified Employee Pension accounts (SEPs), Savings Investment Match Plans for Employees of Small Employers accounts (SIMPLEs) and Tax Sheltered Custodial Accounts (TSCAs); Uniform Gifts to Minors Act (UGMA)/Uniform Transfers to Minors Act (UTMA) accounts for which you, your spouse, or your domestic partner is parent or guardian of the minor child; revocable trust accounts for which you or an immediate family member, individually, is the beneficial owner/grantor; accounts held in the name of your, your spouse’s, or your domestic partner’s sole proprietorship or single owner limited liability company or S corporation; qualified retirement plan assets, provided that you are the sole owner of the business sponsoring the plan, are the sole participant (other than a spouse) in the plan, and have no intention of adding participants to the plan; and investments in wrap accounts.

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As noted in the table below, you can redeem shares of certain classes (see Redeemed Share Class below) and use such redemption proceeds to buy shares of the Corresponding Repurchase Class without paying an otherwise applicable sales charge and/or CDSC (other than, in the case of Direct-at-Fund Accounts, redemptions from Funds that do not assess a front-end sales charge, including Columbia Government Money Market Fund, Columbia Large Cap Enhanced Core Fund, Columbia Large Cap Index Fund, Columbia Mid Cap Index Fund, Columbia Small Cap Index Fund, Columbia Ultra Short Duration Municipal Bond Fund, Columbia Ultra Short Term Bond Fund and Columbia U.S.

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For Class A shares, the Distributor begins to pay these fees immediately after purchase, except in the following case, in which the Distributor begins to pay these fees 12 months after purchase: a purchase of Class A shares of $1 million or more that pay a Class A up-front commission to your financial intermediary and the financial intermediary has opted to receive such commission. The Distributor’s policy to otherwise begin to pay these fees immediately on Class A shares also applies to purchases of funds that do not pay an up-front sales commission on Class A shares, which includes Columbia Government Money Market Fund, Columbia Large Cap Enhanced Core Fund, Columbia Large Cap Index Fund, Columbia Mid Cap Index Fund, Columbia Small Cap Index Fund, Columbia Ultra Short Duration Municipal Bond Fund, Columbia Ultra Short Term Bond Fund and Columbia U.S. Treasury Index Fund. For Class C shares, the Distributor begins to pay these fees 12 months after purchase. However, for Class C shares, financial intermediaries may opt to decline the up-front payment described in Choosing a Share Class – Sales Charges and Commissions – Class C Shares – Commissions and instead may receive these fees immediately after purchase. If the intermediary opts to receive the up-front payment, the Distributor retains the distribution and service fee for the first 12 months following the sale of Class C shares in order to recover the up-front payment made to financial intermediaries and to pay for other related expenses. For Class R shares, the Distributor begins to pay these fees immediately after purchase.

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Generally, each of the Columbia Acorn Funds compensates the Transfer Agent for payments made for Shareholder Services, for each share class except Class Inst3. Effective July 1, 2017, the Columbia Acorn Funds compensate the Transfer Agent for payments made for Shareholder Services as follows:

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Share Price Determination

NAV Calculation

Each of the Fund's share classes calculates its NAV per share as follows:

NAV per share =  (Value of assets of the share class) – (Liabilities of the share class)
Number of outstanding shares of the class

Business Days

A business day is any day that the New York Stock Exchange (NYSE) is open. A business day ends at (i) the scheduled close of the NYSE for such day (usually 4:00 p.m. Eastern Time or such other time as the NYSE may schedule), (ii) the scheduled close of the NYSE (usually 4:00 p.m. Eastern Time) on any business day on which the NYSE has an unscheduled close or intraday trading halt or other disruption, regardless of the time of such unscheduled close, halt or disruption or whether trading resumes, or (iii) such other time as the Board may from time to time determine. On holidays and other days when the NYSE is closed, the Fund’s NAV is not calculated and the Fund does not accept buy or sell orders. However, the value of the Fund’s assets may still be affected on such days to the extent that the Fund holds foreign securities that trade on days that foreign securities markets are open.

Equity securities listed on an exchange are typically valued at the closing price or last trade on their primary exchange at the close of business of the NYSE. Equity securities without a readily available closing price or that are not listed on any exchange are typically valued at the mean between the closing bid and asked prices. Other equity securities, debt securities and other assets are valued differently. For instance, bank loans trading in the secondary market are fair valued unless market quotations are readily available, fixed income investments maturing in 60 days or less are valued primarily using the amortized cost method, unless this methodology results in a valuation that does not approximate the market value of these securities, and those maturing in excess of 60 days are valued based on prices obtained from a pricing service, if available (which may represent market values or fair values). Investments in other open-end funds are valued at their published NAVs. The value of the Fund’s portfolio securities is determined in accordance with the valuation policy approved by the Board (the Valuation Policy). Pursuant to Rule 2a-5 under the 1940 Act, the Board has designated the Investment Manager as the Fund’s valuation designee. The Investment Manager, in turn, has authorized its Valuation Committee to make fair value determinations and to carry out supervisory and certain other functions relating to the valuation of Fund portfolio securities, pursuant to the Valuation Policy.

If a market price is not readily available or is deemed not to reflect market value for a portfolio security, the Investment Manager will determine the price based on a determination of the security's fair value pursuant to the Valuation Policy. In addition, the Investment Manager may use fair valuation techniques to price securities that trade on a foreign exchange when a significant event has occurred after the foreign exchange closes but before the time at which the Fund’s share price is calculated. Foreign exchanges typically close before the time at which Fund share prices are calculated, and may be closed altogether on days when the Fund is open. Such significant events affecting a foreign security may include, but are not limited to: (1) corporate actions, earnings announcements, litigation or other events impacting a single issuer; (2) governmental action that affects securities in one sector or country; (3) natural disasters or armed conflicts affecting a country or region; or (4) significant domestic or foreign market

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fluctuations. The Fund uses various criteria, including an evaluation of U.S. market moves after the close of foreign markets, in determining whether a foreign security's market price is readily available and reflective of market value and, if not, the fair value of the security.

Fair valuation may have the effect of reducing stale pricing arbitrage opportunities presented by the pricing of Fund shares. However, when the Investment Manager uses fair valuation to price equity securities, it may value those securities higher or lower than another fund or manager would. Also, fair valuation of Fund holdings may cause the Fund's performance to diverge to a greater degree from the performance of various benchmark indices used to compare the Fund's performance because indices generally do not use fair valuation techniques. Because of the judgment involved in fair valuation decisions, there can be no assurance that the value ascribed to a particular security is accurate.

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Class C shares are available to the general public for investment, except that Direct-at-Fund Accounts that do not have a financial intermediary assigned to them are not permitted to purchase Class C shares; Class C share purchase orders received from Direct-at-Fund Accounts that do not have a financial intermediary assigned to the account will automatically be invested in Class A shares of the same Fund.

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(b)

The minimum initial investment in Class Adv shares is $2,000 ($1,000 for IRAs; $100 for monthly Systematic Investment Plan accounts) for commissionable brokerage platforms where the financial intermediary, acting as broker on behalf of its customers, charges the customer a commission for effecting transactions in Fund shares, provided that the financial intermediary has an agreement with the Distributor that specifically authorizes offering Class Adv shares within such platform; for all other eligible Class Adv share investors (see Buying Shares – Eligible Investors – Class Adv Shares above), there is no minimum initial investment. The minimum initial investment amount for Class Inst shares is $0, $1,000 or $2,000 depending upon the category of eligible investor. See — Class Inst Shares Minimum Initial Investments below. The minimum initial investment amount for monthly Systematic Investment Plan accounts is the same as the amount set forth in the first two rows of the table, as applicable.

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■

A sales charge may apply when you exchange shares of a Fund that were not assessed a sales charge at the time you purchased such shares. If you invest through a Direct-at-Fund Account in Columbia Government Money Market Fund, Columbia Large Cap Enhanced Core Fund, Columbia Large Cap Index Fund, Columbia Mid Cap Index Fund, Columbia Small Cap Index Fund, Columbia Ultra Short Duration Municipal Bond Fund, Columbia Ultra Short Term Bond Fund, Columbia U.S. Treasury Index Fund or any other Columbia Fund that does not impose a front-end sales charge and then you exchange into a Fund that does assess a sales charge, your transaction is subject to a front-end sales charge if you exchange into Class A shares and to a CDSC if you exchange into Class C shares of the Columbia Funds.

■

If you purchased Class A shares of a Columbia Fund that imposes a front-end sales charge (and you paid any applicable sales charge) and you then exchange those shares into Columbia Government Money Market Fund, Columbia Large Cap Enhanced Core Fund, Columbia Large Cap Index Fund, Columbia Mid Cap Index Fund, Columbia Small Cap Index Fund, Columbia Ultra Short Duration Municipal Bond Fund, Columbia Ultra Short Term Bond Fund, Columbia U.S. Treasury Index Fund or any other Columbia Fund that does not impose a front-end sales charge, you may exchange that amount to Class A of another Fund in the future, including dividends earned on that amount, without paying a sales charge.

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Distributions to Shareholders

The Fund intends to pay out, in the form of distributions to shareholders, a sufficient amount of its income and gains so that the Fund will qualify for treatment as a regulated investment company and generally will not have to pay any federal income or excise tax. The Fund generally intends to distribute any net realized capital gain (whether long-term or short-term gain) at least once a year. Normally, the Fund will declare and pay distributions of net investment income according to the following schedule:

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■

Distributions of the Fund's ordinary income and net short-term capital gain, if any, generally are taxable to you as ordinary income. Distributions of the Fund's net long-term capital gain, if any, generally are taxable to you as long-term capital gain. Whether capital gains are long-term or short-term is determined by how long the Fund has owned the investments that generated them, rather than how long you have owned your shares. Certain events may require the Fund to sell significant amounts of appreciated securities and make large dividends relative to the Fund’s NAV. Such events may include large net shareholder redemptions, portfolio rebalancing or fund mergers. The Fund generally provides estimates of expected capital gain dividends (if any) prior to the distribution on columbiathreadneedleus.com.

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Taxes

The information provided above is only a summary of how U.S. federal income taxes may affect your investment in the Fund. It is not intended as a substitute for careful tax planning. Your investment in the Fund may have other tax implications. It does not apply to certain types of investors who may be subject to special rules, including foreign or tax-exempt investors or those holding Fund shares through a tax-advantaged account, such as a 401(k) plan or IRA. Please see the SAI for more detailed tax information. You should consult with your own tax advisor about the particular tax consequences to you of an investment in the Fund, including the effect of any foreign, state and local taxes, and the effect of possible changes in applicable tax laws.

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The financial highlights table is intended to help you understand the Fund’s financial performance for the past five fiscal years. Certain information reflects financial results for a single Fund share. Per share net investment income (loss) amounts are calculated based on average shares outstanding during the period. The total return in the table represents the rate that an investor would have earned (or lost) on an investment in the Fund assuming all dividends and distributions had been reinvested. Total return does not reflect payment of sales charges, if any. Total return and portfolio turnover are not annualized for periods of less than one year. The portfolio turnover rate is calculated without regard to purchase and sales transactions of short-term instruments and certain derivatives, if any. If such transactions were included, the Fund’s portfolio turnover rate might be higher. The names of certain share classes may have changed during the periods shown below (see Appendix S to the SAI for details). This information has been audited by PricewaterhouseCoopers LLP, an independent registered public accounting firm, whose report, along with the Fund’s financial statements, is included in the Fund’s annual report, which is available upon request. The independent registered public accounting firm’s report and the Fund’s financial statements are also incorporated by reference into the SAI.

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	Net asset value, beginning of period	Net investment income (loss)	Net realized and unrealized gain (loss)	Total from investment operations	Distributions from net investment income	Total distributions to shareholders
Class A
Year Ended 12/31/2022	$33.33	0.06(c)	(12.78)	(12.72)	—	—
Year Ended 12/31/2021	$27.49	(0.14)	6.04	5.90	(0.06)	(0.06)
Year Ended 12/31/2020	$22.52	(0.12)	5.22	5.10	(0.13)	(0.13)
Year Ended 12/31/2019	$15.56	0.06	7.09	7.15	(0.19)	(0.19)
Year Ended 12/31/2018	$19.27	0.11	(3.70)	(3.59)	(0.12)	(0.12)
Advisor Class
Year Ended 12/31/2022	$33.68	0.11(c)	(12.92)	(12.81)	—	—
Year Ended 12/31/2021	$27.78	(0.10)	6.13	6.03	(0.13)	(0.13)
Year Ended 12/31/2020	$22.70	(0.06)	5.27	5.21	(0.13)	(0.13)
Year Ended 12/31/2019	$15.68	0.12	7.13	7.25	(0.23)	(0.23)
Year Ended 12/31/2018	$19.36	0.19	(3.75)	(3.56)	(0.12)	(0.12)
Class C
Year Ended 12/31/2022	$32.35	(0.10) (c)	(12.40)	(12.50)	—	—
Year Ended 12/31/2021	$26.83	(0.36)	5.88	5.52	—	—
Year Ended 12/31/2020	$22.15	(0.27)	5.08	4.81	(0.13)	(0.13)
Year Ended 12/31/2019	$15.33	(0.06)	6.93	6.87	(0.05)	(0.05)
Year Ended 12/31/2018	$19.12	(0.02)	(3.65)	(3.67)	(0.12)	(0.12)
Institutional Class
Year Ended 12/31/2022	$33.51	0.11(c)	(12.85)	(12.74)	—	—
Year Ended 12/31/2021	$27.64	(0.06)	6.06	6.00	(0.13)	(0.13)
Year Ended 12/31/2020	$22.59	(0.06)	5.24	5.18	(0.13)	(0.13)
Year Ended 12/31/2019	$15.60	0.12	7.10	7.22	(0.23)	(0.23)
Year Ended 12/31/2018	$19.27	0.15	(3.70)	(3.55)	(0.12)	(0.12)
Institutional 2 Class
Year Ended 12/31/2022	$33.92	0.12(c)	(13.00)	(12.88)	—	—
Year Ended 12/31/2021	$27.98	(0.12)	6.21	6.09	(0.15)	(0.15)
Year Ended 12/31/2020	$22.84	(0.05)	5.32	5.27	(0.13)	(0.13)
Year Ended 12/31/2019	$15.78	0.14	7.17	7.31	(0.25)	(0.25)
Year Ended 12/31/2018	$19.46	0.19	(3.75)	(3.56)	(0.12)	(0.12)

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	Net asset value, end of period	Total return(a)	Total gross expense ratio to average net assets(b)	Total net expense ratio to average net assets(b)	Net investment income (loss) ratio to average net assets	Portfolio turnover	Net assets, end of period (000's)
Class A
Year Ended 12/31/2022	$20.61	(38.16%)	1.80% (d), (e)	1.45% (d), (e), (f)	0.25%	31%	$28,892
Year Ended 12/31/2021	$33.33	21.47%	1.63% (e)	1.44% (e), (f)	(0.45%)	21%	$66,374
Year Ended 12/31/2020	$27.49	22.80%	1.86% (e)	1.45% (e)	(0.54%)	45%	$42,059
Year Ended 12/31/2019	$22.52	45.96%	1.88%	1.44%	0.33%	30%	$33,361
Year Ended 12/31/2018	$15.56	(18.78%)	1.81% (e)	1.45% (e)	0.57%	39%	$22,870
Advisor Class
Year Ended 12/31/2022	$20.87	(38.03%)	1.55% (d), (e)	1.20% (d), (e), (f)	0.47%	31%	$1,161
Year Ended 12/31/2021	$33.68	21.75%	1.37% (e)	1.19% (e), (f)	(0.32%)	21%	$3,083
Year Ended 12/31/2020	$27.78	23.10%	1.61% (e)	1.20% (e)	(0.29%)	45%	$1,781
Year Ended 12/31/2019	$22.70	46.30%	1.63%	1.19%	0.60%	30%	$1,906
Year Ended 12/31/2018	$15.68	(18.53%)	1.55% (e)	1.19% (e)	0.97%	39%	$1,496
Class C
Year Ended 12/31/2022	$19.85	(38.64%)	2.54% (d), (e)	2.20% (d), (e), (f)	(0.47%)	31%	$2,372
Year Ended 12/31/2021	$32.35	20.57%	2.39% (e)	2.19% (e), (f)	(1.20%)	21%	$7,078
Year Ended 12/31/2020	$26.83	21.87%	2.61% (e)	2.20% (e)	(1.27%)	45%	$5,705
Year Ended 12/31/2019	$22.15	44.79%	2.64%	2.19%	(0.30%)	30%	$6,186
Year Ended 12/31/2018	$15.33	(19.34%)	2.56% (e)	2.20% (e)	(0.12%)	39%	$8,770
Institutional Class
Year Ended 12/31/2022	$20.77	(38.02%)	1.54% (d), (e)	1.20% (d), (e), (f)	0.46%	31%	$38,307
Year Ended 12/31/2021	$33.51	21.76%	1.38% (e)	1.19% (e), (f)	(0.21%)	21%	$111,462
Year Ended 12/31/2020	$27.64	23.08%	1.61% (e)	1.20% (e)	(0.29%)	45%	$55,171
Year Ended 12/31/2019	$22.59	46.35%	1.63%	1.19%	0.64%	30%	$49,616
Year Ended 12/31/2018	$15.60	(18.57%)	1.56% (e)	1.20% (e)	0.80%	39%	$32,813
Institutional 2 Class
Year Ended 12/31/2022	$21.04	(37.97%)	1.40% (d), (e)	1.14% (d), (e)	0.48%	31%	$2,863
Year Ended 12/31/2021	$33.92	21.80%	1.32% (e)	1.14% (e)	(0.38%)	21%	$25,882
Year Ended 12/31/2020	$27.98	23.23%	1.58% (e)	1.14% (e)	(0.24%)	45%	$3,855
Year Ended 12/31/2019	$22.84	46.33%	1.60%	1.13%	0.73%	30%	$2,175
Year Ended 12/31/2018	$15.78	(18.44%)	1.50% (e)	1.13% (e)	0.96%	39%	$2,554

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	Net asset value, beginning of period	Net investment income (loss)	Net realized and unrealized gain (loss)	Total from investment operations	Distributions from net investment income	Total distributions to shareholders
Institutional 3 Class
Year Ended 12/31/2022	$33.38	0.13(c)	(12.80)	(12.67)	—	—
Year Ended 12/31/2021	$27.54	(0.05)	6.05	6.00	(0.16)	(0.16)
Year Ended 12/31/2020	$22.48	(0.02)	5.21	5.19	(0.13)	(0.13)
Year Ended 12/31/2019	$15.53	0.14	7.06	7.20	(0.25)	(0.25)
Year Ended 12/31/2018	$19.17	(0.04)	(3.48)	(3.52)	(0.12)	(0.12)

Notes to Financial Highlights
(a)	Had the Investment Manager and/or Transfer Agent not waived fees and/or reimbursed a portion of expenses, total return would have been reduced.
(b)	In addition to the fees and expenses that the Fund bears directly, the Fund indirectly bears a pro rata share of the fees and expenses of any other funds in which it invests, if any. Such indirect expenses are not included in the Fund's reported expense ratios.
(c)	Net investment income per share includes special dividends. The effect of these dividends amounted to $0.01 per share.
(d)	Ratios include Trustees’ fees deferred during the current period as well as any gains or losses on the Trustees’ deferred compensation balances as a result of market fluctuations. If these had been excluded, expenses would have been higher by 0.01%.
(e)	Ratios include line of credit interest expense which is less than 0.01%.
(f)	The benefits derived from expense reductions had an impact of less than 0.01%.

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	Net asset value, end of period	Total return(a)	Total gross expense ratio to average net assets(b)	Total net expense ratio to average net assets(b)	Net investment income (loss) ratio to average net assets	Portfolio turnover	Net assets, end of period (000's)
Institutional 3 Class
Year Ended 12/31/2022	$20.71	(37.96%)	1.47% (d), (e)	1.11% (d), (e)	0.56%	31%	$41
Year Ended 12/31/2021	$33.38	21.83%	1.32% (e)	1.10% (e)	(0.15%)	21%	$60
Year Ended 12/31/2020	$27.54	23.24%	1.52% (e)	1.10% (e)	(0.08%)	45%	$69
Year Ended 12/31/2019	$22.48	46.42%	1.54%	1.09%	0.74%	30%	$19
Year Ended 12/31/2018	$15.53	(18.51%)	1.41% (e)	1.08% (e)	(0.21%)	39%	$3

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As noted in the Choosing a Share Class section of the prospectus, the sales charge reductions and waivers available to investors who purchase and hold their Fund shares through different financial intermediaries may vary. This Appendix A describes financial intermediary-specific reductions and/or waiver policies applicable to Fund shares purchased and held through the particular financial intermediary. A reduction and/or waiver that is specific to a particular financial intermediary is not available to Direct-at-Fund Accounts and does not apply in any case to non-omnibus positions wherever held. These reductions and/or waivers may apply to purchases, sales, and exchanges of Fund shares. A shareholder transacting in Fund shares through a financial intermediary identified below should carefully read the terms and conditions of the reductions and/or waivers. Please consult your financial intermediary with respect to any sales charge reduction/waiver described below.

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© 2023 Columbia Management Investment Advisers, LLC. All rights reserved.

PRO109_12_N01_(05/23)

Columbia 
  Acorn® Fund

As with all mutual funds, the Securities and Exchange Commission (SEC) has not approved or disapproved these securities or passed upon the adequacy of this prospectus. Any representation to the contrary is a criminal offense.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Adv	Class C	Class Inst	Class Inst2	Class Inst3
Management fees	0.68%	0.68%	0.68%	0.68%	0.68%	0.68%
Distribution and/or service (12b-1) fees	0.25%	0.00%	1.00%	0.00%	0.00%	0.00%
Other expenses	0.15%	0.15%	0.15%	0.15%	0.12%	0.07%
Total annual Fund operating expenses	1.08%	0.83%	1.83%	0.83%	0.80%	0.75%

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	1 year	3 years	5 years	10 years
Class C (assuming no redemption of shares)	$186	$576	$990	$1,951
Class Inst (whether or not shares are redeemed)	$85	$265	$460	$1,025
Class Inst2 (whether or not shares are redeemed)	$82	$255	$444	$990
Class Inst3 (whether or not shares are redeemed)	$77	$240	$417	$930

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Consumer Discretionary Sector. The Fund is more susceptible to the particular risks that may affect companies in the consumer discretionary sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the consumer discretionary sector are subject to certain risks, including fluctuations in the performance of the overall domestic and international economies, interest rate changes, increased competition and consumer confidence. Performance of such companies may be affected by factors including reduced disposable household income, reduced consumer spending, and changing demographics and consumer tastes.

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Health Care Sector. The Fund is more susceptible to the particular risks that may affect companies in the health care sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the health care sector are subject to certain risks, including restrictions on government reimbursement for medical expenses, government approval of medical products and services, competitive pricing pressures, and the rising cost of medical products and services (especially for companies dependent upon a relatively limited number of products or services), among others. Performance of such companies may be affected by factors including government regulation, obtaining and protecting patents (or the failure to do so), product liability and other similar litigation as well as product obsolescence.

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Industrials Sector. The Fund is more susceptible to the particular risks that may affect companies in the industrials sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the industrials sector are subject to certain risks, including changes in supply and demand for their specific product or service and for industrial sector products in general, including decline in demand for such products due to rapid technological developments and frequent new product introduction. Performance of such companies may be affected by factors including government regulation, world events, economic conditions and risks for environmental damage and product liability claims.

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Year by Year Total Return (%) as of December 31 Each Year*	Best and Worst Quarterly Returns During the Period Shown in the Bar Chart
	Best	2nd Quarter 2020	28.34%
	Worst	2nd Quarter 2022	-23.57%

*	Year to Date return as of March 31, 2023: 10.03%

	Share Class Inception Date	1 Year	5 Years	10 Years
Class Inst	06/10/1970
returns before taxes		-33.78%	2.35%	7.27%
returns after taxes on distributions		-34.58%	-0.75%	2.73%
returns after taxes on distributions and sale of Fund shares		-19.46%	2.20%	5.36%
Class A returns before taxes	10/16/2000	-37.80%	0.89%	6.35%
Class Adv returns before taxes	11/08/2012	-33.79%	2.36%	7.24%
Class C returns before taxes	10/16/2000	-35.10%	1.34%	6.19%
Class Inst2 returns before taxes	11/08/2012	-33.83%	2.38%	7.29%
Class Inst3 returns before taxes	11/08/2012	-33.77%	2.44%	7.35%
Russell 2500 Growth Index (reflects no deductions for fees, expenses or taxes)		-26.21%	5.97%	10.62%

Portfolio Management		Title		Role with Fund		Service with the Fund Since
Erika K. Maschmeyer, CFA		Head of Domestic Equity and Director of Domestic Research, Portfolio Manager and Analyst at the Investment Manager		Lead Portfolio Manager since February 2023		2016
John L. Emerson, CFA		Portfolio Manager and Analyst at the Investment Manager		Portfolio Manager since 2021		2003

8	Prospectus 2023

Online		Regular Mail		Express Mail		By Telephone
columbiathreadneedleus.com/investor/		Columbia Management Investment Services Corp. P.O. Box 219104 Kansas City, MO 64121-9104		Columbia Management Investment Services Corp. c/o SS&C GIDS, Inc. 430 W 7th Street, Suite 219104 Kansas City, MO 64105-1407		800.422.3737

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Investment Objective

Under normal circumstances, the Fund invests a majority of its net assets in the common stock of small- and mid-sized companies with market capitalizations generally in the range of market capitalizations in the Russell 2500 Growth Index, the Fund's benchmark, (the Index) at the time of purchase (between $5.5 million and $24 billion as of March 31, 2023). The market capitalization range and composition of companies in the Index are subject to change.

As such, the size of the companies in which the Fund invests may change. The Fund determines a company’s market capitalization at the time of investment. As long as a majority of its net assets are invested in companies within the market capitalization range of the Index, the Fund may continue to hold and make new investments in a security even if the company’s market capitalization grows beyond the market capitalization of the largest company within the range of the Index or falls below the market capitalization of the smallest company within the Index.

Columbia Wanger Asset Management, LLC, the Fund's investment adviser (the Investment Manager), believes that stocks of small- and mid-sized companies, which generally are not as well known by financial analysts as larger companies, may offer higher return potential than stocks of larger companies. The Fund invests the majority of its assets in U.S. companies, but also may invest up to 33% of its total assets in foreign companies in developed markets (for example, Japan, Canada and the United Kingdom) and in emerging markets (for example, China, India and Brazil). The Investment Manager from time to time emphasizes one or more sectors in selecting the Fund’s investments, including the consumer discretionary, health care, industrials, and information technology sectors.