Summary Prospectus

May 1, 2025

Columbia Acorn® Fund

 

Class	Ticker Symbol
A	LACAX
C	LIACX
Institutional (Class Inst)	ACRNX
Institutional 2 (Class Inst2)	CRBRX
Institutional 3 (Class Inst3)	CRBYX
S	ACRSX

Before you invest, you may want to review the Fund’s prospectus, which contains more information about the Fund and its risks. You can find the Fund’s prospectus, reports to shareholders, statement of additional information and other information about the Fund online at https://www.columbiathreadneedleus.com/resources/literature. If you hold your Fund shares through a financial intermediary (such as a broker-dealer or bank), you can get this information at no cost by contacting that financial intermediary. If you hold your Fund shares directly with the Fund, you can get this information at no cost by calling 800.345.6611 or by sending an email to serviceinquiries@columbiathreadneedle.com. This Summary Prospectus incorporates by reference the Fund’s prospectus, dated May 1, 2025, and current Statement of Additional Information.

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

 

Investment Objective

Columbia Acorn® Fund (the Fund) seeks long-term capital appreciation.

Fees and Expenses of the Fund

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 21 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 Waiversbeginning on page S-1. 

Shareholder Fees (fees paid directly from your investment)
	Class A	Class C	Classes Inst, Inst2, Inst3, and S
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75 %	None	None
Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)	1.00 %(a)	1.00 %(b)	None

 

Annual Fund Operating Expenses(c) (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class C	Class Inst	Class Inst2	Class Inst3	Class S
Management fees	0.72 %	0.72 %	0.72 %	0.72 %	0.72 %	0.72 %
Distribution and/or service (12b-1) fees	0.25 %	1.00 %	0.00 %	0.00 %	0.00 %	0.00 %
Other expenses(c)	0.13 %	0.13 %	0.13 %	0.09 %	0.05 %	0.13 %
Total annual Fund operating expenses(d)	1.10 %	1.85 %	0.85 %	0.81 %	0.77 %	0.85 %
Less: Fee waivers and/or expense reimbursements(e)	(0.03 %)	(0.03 %)	(0.03 %)	(0.03 %)	(0.03 %)	(0.03 %)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.07 %	1.82 %	0.82 %	0.78 %	0.74 %	0.82 %

(a)

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.

(b)

This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.

(c)

Expenses have been restated based on estimated amounts for the Fund's current fiscal year.

(d)

“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.

(e)

Columbia Wanger Asset Management, LLC (the Investment Manager) 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 April 30, 2027, unless sooner terminated at the sole discretion of the Fund’s Board of Trustees. Under this agreement, the Fund’s net operating expenses, subject to applicable exclusions, will not exceed the annual rates of 1.07% for Class A, 1.82% for Class C, 0.82% for Class Inst, 0.78% for Class Inst2, 0.74% for Class Inst3 and 0.82% for Class S. Any difference 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.

 Example

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:

■

you invest $10,000 in the applicable class of Fund shares for the periods indicated,

■

your investment has a 5% return each year, and

■

the Fund’s total annual operating expenses remain the same as shown in the Annual Fund Operating Expensestable above.

1

Columbia Acorn® Fund

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 two years of the other examples. Although your actual costs may be higher or lower, based on the assumptions listed above, your costs would be: 

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$678	$899	$1,141	$1,833
Class C (assuming redemption of all shares at the end of the period)	$285	$576	$995	$1,968
Class C (assuming no redemption of shares)	$185	$576	$995	$1,968
Class Inst (whether or not shares are redeemed)	$84	$265	$465	$1,043
Class Inst2 (whether or not shares are redeemed)	$80	$252	$444	$996
Class Inst3 (whether or not shares are redeemed)	$76	$240	$422	$948
Class S (whether or not shares are redeemed)	$84	$265	$465	$1,043

Portfolio Turnover

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 81% of the average value of its portfolio.

Principal Investment Strategies

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 Index) at the time of purchase (between $5.2 million and $31.9 billion as of March 31, 2025).The market capitalization range and composition of companies in the Index are subject to change.

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 Fund may at times emphasize one or more sectors in selecting its investments, including the consumer discretionary, health care, industrials, and information technology sectors.

Principal Risks

An investment in the Fund involves risks, including Small- and Mid-Cap Stock Risk, and Market Risk, among others. Descriptions of these and other principal risks of investing in the Fund are provided below. There is no assurance that the Fund will achieve its investment objective and you may lose money. The value of the Fund’s holdings may decline, and the Fund’s net asset value (NAV) and share price may go down. 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. The significance of any specific risk to an investment in the Fund will vary over time depending on the composition of the Fund's portfolio, market conditions, and other factors. You should read all of the risk information below carefully, because any one or more of these risks may result in losses to the Fund.

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.

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.

Columbia Acorn® Fund

2

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.

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.

■

Small- and Mid-Cap Stock Risk. Investments in small- and mid-capitalization companies (small- and mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small- and mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. Securities of small- and mid-cap companies may be less liquid and more volatile than the securities of larger companies.

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.

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 consumer discretionary, health care, industrials, and information technology sectors. Companies in the same sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund vulnerable to unfavorable developments in that industry, group of industries or economic sector.

■

Consumer Discretionary Sector. The Fund is vulnerable to the particular risks that may affect companies in the consumer discretionary sector. 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.

■

Health Care Sector. The Fund is vulnerable to the particular risks that may affect companies in the health care sector. 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.

■

Industrials Sector. The Fund is vulnerable to the particular risks that may affect companies in the industrials sector. 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.

■

Information Technology Sector. The Fund is vulnerable to the particular risks that may affect companies in the information technology sector. Companies in the information technology sector are subject to certain risks,

3

Columbia Acorn® Fund

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.

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 Inst share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns 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.

Effective August 1, 2024, the Fund compares its performance to the Russell 3000® Index, a broad-based performance index, as required by new regulatory requirements. The Fund’s performance also continues to be compared to its prior benchmark, which management believes more closely represents the market sectors and/or asset classes in which the Fund primarily invests.

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 (adjusted to reflect the higher class-related operating expenses of such share classes, where applicable) for periods prior to its inception date. Share classes with expenses that are higher than Class Inst shares will have performance that is lower than Class Inst shares.

Except for differences in fees and expenses, all 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.

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 Inst 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.Updated performance information can be obtained by calling toll-free 800.345.6611 or visiting columbiathreadneedleus.com. 

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%

Columbia Acorn® Fund

4

 Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2024)

 

	Share Class Inception Date	1 Year	5 Years	10 Years
Class Inst	06/10/1970
returns before taxes		14.46%	5.45%	7.86%
returns after taxes on distributions		14.46%	3.37%	3.84%
returns after taxes on distributions and sale of Fund shares		8.56%	4.14%	5.25%
Class A returns before taxes	10/16/2000	7.55%	3.95%	6.95%
Class C returns before taxes	10/16/2000	12.28%	4.40%	6.78%
Class Inst2 returns before taxes	11/08/2012	14.51%	5.48%	7.89%
Class Inst3 returns before taxes	11/08/2012	14.50%	5.51%	7.94%
Class S returns before taxes	10/02/2024	14.46%	5.45%	7.86%
Russell 2500® Growth Index (reflects no deductions for fees, expenses or taxes)		13.90%	8.08%	9.45%
Russell 3000® Index (reflects no deductions for fees, expenses or taxes)		23.81%	13.86%	12.55%

 

Fund Management

Investment Manager: Columbia Wanger Asset Management, LLC 

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	Portfolio Manager or Lead Portfolio Manager since 2019	2016

Purchase and Sale of Fund Shares

You may purchase or redeem shares of the Fund on any business day by contacting the Fund in the ways described below: 

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. 801 Pennsylvania Ave., STE. 219104 Kansas City, MO 64105-1307	800.422.3737

You may purchase shares and receive redemption proceeds by electronic funds transfer, by check or by wire. If you maintain your account with a broker-dealer or other financial intermediary, you must contact that financial intermediary to buy, sell or exchange shares of the Fund through your account with the intermediary.

The minimum initial investment amounts for the share classes offered by the Fund are shown below:

Minimum Initial Investment 

Class	Category of eligible account	For accounts other than Systematic Investment Plan accounts (as described in the Fund’s Prospectus)	For Systematic Investment Plan accounts
Classes A & C	All accounts other than IRAs	$2,000	$100
	IRAs	$1,000	$100
Class Inst	All eligible accounts	$0, $1,000 or $2,000 depending upon the category of eligible investor	$100
Class Inst2	All eligible accounts	None	N/A
Class Inst3	All eligible accounts	$0, $1,000, $2,000 or $1 million depending upon the category of eligible investor	$100 (for certain eligible investors)

 

More information about these minimums can be found in the Buying, Selling and Exchanging Shares - Buying Sharessection of the prospectus. There is no minimum additional investment for any share class.

5

Columbia Acorn® Fund

Class S shares are available (i) to be held, but not purchased, by accounts of financial intermediaries that, with specific written permission from the Distributor, have instructed the Fund to exchange Class Inst shares for Class S shares; and (ii) to be held and purchased by omnibus group retirement plans that (A) opened and, subject to exceptions, funded a Class Inst share account as of the close of business on March 28, 2013 and have continuously held Class Inst shares in such account through at least September 30, 2024 and (B) received specific written permission from the Distributor to exchange Class Inst shares for Class S shares. Only omnibus retirement plans referenced in (ii) above may purchase Class S shares, open new Class S accounts, or add new plan participants to a Class S shares omnibus retirement plan account. Otherwise, Class S shares are not available for purchase (other than through the reinvestment of distributions on Class S shares).

Tax Information

The Fund normally distributes net investment income and net realized capital gains, if any, to shareholders. These distributions are generally taxable to you as ordinary income, qualified dividend income or capital gains, unless you are investing through a tax-advantaged account, such as a 401(k) plan or an IRA. If you are investing through a tax-advantaged account, you may be taxed upon withdrawals from that account.

Payments to Broker-Dealers and Other Financial Intermediaries

If you purchase the Fund through a broker-dealer or other financial intermediary (such as a bank), the Fund and its related companies — including Columbia Wanger Asset Management, LLC (the Investment Manager), Columbia Management Investment Distributors, Inc. (the Distributor) and Columbia Management Investment Services Corp. (the Transfer Agent) — may pay the intermediary for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your financial advisor to recommend the Fund over another investment. Ask your financial advisor or visit your financial intermediary’s website for more information.

Columbia Acorn® Fund

6

 

Columbia Threadneedle Investments is the global brand name of the Columbia and Threadneedle group of companies.

The Fund is distributed by Columbia Management Investment Distributors, Inc., 290 Congress Street, Boston, MA 02210.

© 2025 Columbia Management Investment Advisers, LLC. All rights reserved. columbiathreadneedleus.comSUM110_12_R01_(05/25)