EX h.4

Columbia Wanger Asset Management, LLC

227 West Monroe

Suite 3000

Chicago, IL 60606-5016

T: 312.634.9200

columbiathreadneedle.com

April 30, 2017

Columbia Acorn Trust

227 W. Monroe Street

Suite 3300

Chicago, Illinois 60606

Ladies and Gentlemen:

Columbia Wanger Asset Management, LLC (“CWAM”) hereby contractually undertakes as of the date hereof with respect to Columbia Thermostat Fund, a series of Columbia Acorn Trust (the “Fund”), to waive fees and reimburse certain expenses of the Fund, through April 30, 2018 such that total Fund 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) do not exceed the annual rates of:

• 0.50% of the Fund’s average daily net assets attributable to Class A shares;

• 1.25% of the Fund’s average daily net assets attributable to Class C shares;

• 0.25% of the Fund’s average daily net assets attributable to Class R4 shares;

• 0.23% of the Fund’s average daily net assets attributable to Class R5 shares;

• 0.18% of the Fund’s average daily net assets attributable to Class Y shares; and

• 0.25% of the Fund’s average daily net assets attributable to Class Z shares.

Notwithstanding the foregoing, the limitations on total ordinary operating expenses set forth herein shall not apply to any class of shares of a Fund established after the effective date hereof.

Effective April 30, 2017, this contractual undertaking supersedes any prior contractual expense limitation provisions for the Fund. This undertaking shall be binding upon any successors and assignees of CWAM.

Very truly yours,
COLUMBIA WANGER ASSET MANAGEMENT, LLC
	By:	/S/ P. Zachary Egan
		P. Zachary Egan
		President

Agreed and accepted by

COLUMBIA ACORN TRUST, on behalf of its series Columbia Thermostat Fund

By:	/S/ John Kunka
	John Kunka
	Vice President and Treasurer