Summary Prospectus by Investment Company (Form 497K)

Supplement dated June 30, 2026

to the Prospectus and Summary Prospectus of the following fund (the Fund): 

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Acorn® Fund	May 1, 2026

Effective immediately, the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

The portfolio manager information under the caption "Fund Management" in the Summary Prospectus and in the "Summary of Columbia Acorn® Fund" section of the Prospectus is hereby superseded and replaced with the following: 

Portfolio Management	Title	Role with Fund	Managed Fund Since
Nicolas Janvier, CFA	Head of North America Equities	Portfolio Manager	June 2026
Pratyasha Rath	Portfolio Manager	Portfolio Manager	September 2025

The portfolio manager information for Columbia Acorn® Fund under the "Primary Service Provider Contracts" caption in the "More Information About the Funds" section of the Prospectus is hereby revised with the following:

Portfolio Managers

Information about the portfolio managers primarily responsible for overseeing the Fund's investments is shown below. The SAI provides additional information about the portfolio managers, including information relating to compensation, other accounts managed by the portfolio managers, and ownership by the portfolio managers of Fund shares. 

Portfolio Management	Title	Role with Fund	Managed Fund Since
Nicolas Janvier, CFA	Head of North America Equities	Portfolio Manager	June 2026
Pratyasha Rath	Portfolio Manager	Portfolio Manager	September 2025

Mr. Janvier joined Threadneedle Asset Management Limited, a Participating Affiliate, in 2014 as a portfolio manager. Mr. Janvier began his investment career in 2000 and earned a B.A. from the University of Florida.

Ms. Rath has been associated with the Investment Manager or one of its affiliates since 2017. Ms. Rath began her investment career in 2007 and earned a B.A. from Delhi University, India and an M.S. from the Illinois Institute of Technology, Chicago.

The rest of the Prospectus and Summary Prospectus remain unchanged.

Shareholders should retain this Supplement for future reference.