rr_RiskReturnAbstract

rr_SupplementToProspectusTextBlock

Supplement dated March 3, 2025

to the Prospectus and Summary Prospectus, each as supplemented, of the following fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Acorn® Fund	5/1/2024

Effective immediately (unless a different date is otherwise noted), the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

The information in the Fees and Expenses table and under the heading "Example" in the “Fees and Expenses of the Fund” section of the Summary Prospectus and in the “Summary of the Fund – Fees and Expenses of the Fund” section of the Prospectus is hereby superseded and replaced with the following:

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(d)	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(d)	0.13 %	0.13 %	0.13 %	0.09 %	0.05 %	0.13 %
Total annual Fund operating expenses(e)	1.10 %	1.85 %	0.85 %	0.81 %	0.77 %	0.85 %
Less: Fee waivers and/or expense reimbursements(f)	(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)

Management fees include an advisory fee of 0.67% and administrative services fee of 0.05%. As a result of combining those fees as management fees, other expenses do not include administrative services fee.

(e)

“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.

(f)

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 Expenses table above.

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

The rest of the section remains the same.

Supplement dated March 3, 2025

to the Prospectus and Summary Prospectus, each as supplemented, of the following fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Acorn European FundSM	5/1/2024

Effective immediately (unless a different date is otherwise noted), the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

Shareholder Fees (fees paid directly from your investment)
	Class A	Class Inst
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75 %	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)	None

Annual Fund Operating Expenses(b) (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Inst
Management fees(c)	0.97 %	0.97 %
Distribution and/or service (12b-1) fees	0.25 %	0.00 %
Other expenses(c)	0.39 %	0.39 %
Total annual Fund operating expenses(d)	1.61 %	1.36 %
Fee waivers and/or expense reimbursements(e)	(0.24 %)	(0.24 %)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.37 %	1.12 %

(a)

(b)

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

(c)

Management fees include an advisory fee of 0.92% and administrative services fee of 0.05%. As a result of combining those fees as management fees, other expenses do not include administrative services fee.

(d)

(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 1.37% for Class A and 1.12% for Class Inst. 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

■

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 Expenses table above.

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)	$706	$1,008	$1,357	$2,337
Class Inst (whether or not shares are redeemed)	$114	$382	$698	$1,592

The rest of the section remains the same.

Supplement dated March 3, 2025

to the Prospectus and Summary Prospectus, each as supplemented, of the following fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Acorn International®	5/1/2024

Effective immediately (unless a different date is otherwise noted), the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

Shareholder Fees (fees paid directly from your investment)
	Class A	Classes Inst, Inst2, Inst3 and S
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75 %	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)	None

Annual Fund Operating Expenses(b) (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Inst	Class Inst2	Class Inst3	Class S
Management fees(c)	0.85 %	0.85 %	0.85 %	0.85 %	0.85 %
Distribution and/or service (12b-1) fees	0.25 %	0.00 %	0.00 %	0.00 %	0.00 %
Other expenses(c)	0.20 %	0.20 %	0.13 %	0.09 %	0.20 %
Total annual Fund operating expenses(d)	1.30 %	1.05 %	0.98 %	0.94 %	1.05 %
Less: Fee waivers and/or expense reimbursements(e)	(0.08 %)	(0.08 %)	(0.09 %)	(0.10 %)	(0.08 %)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.22 %	0.97 %	0.89 %	0.84 %	0.97 %

(a)

(b)

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

(c)

Management fees include an advisory fee of 0.80% and administrative services fee of 0.05%. As a result of combining those fees as management fees, other expenses do not include administrative services fee.

(d)

(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 1.22% for Class A, 0.97% for Class Inst, 0.89% for Class Inst2, 0.84% for Class Inst3 and 0.97% 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

■

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 Expenses table above.

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$692	$948	$1,232	$2,039
Class Inst (whether or not shares are redeemed)	$99	$318	$563	$1,268
Class Inst2 (whether or not shares are redeemed)	$91	$294	$524	$1,185
Class Inst3 (whether or not shares are redeemed)	$86	$279	$500	$1,136
Class S (whether or not shares are redeemed)	$99	$318	$563	$1,268

The rest of the section remains the same.

Supplement dated March 3, 2025

to the Prospectus and Summary Prospectus, each as supplemented, of the following fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Acorn International SelectSM	5/1/2024

Effective immediately (unless a different date is otherwise noted), the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

Shareholder Fees (fees paid directly from your investment)
	Class A	Classes Inst, Inst2, Inst3 and S
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75 %	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)	None

Annual Fund Operating Expenses(b) (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Inst	Class Inst2	Class Inst3	Class S
Management fees(c)	0.87 %	0.87 %	0.87 %	0.87 %	0.87 %
Distribution and/or service (12b-1) fees	0.25 %	0.00 %	0.00 %	0.00 %	0.00 %
Other expenses(c)	0.32 %	0.32 %	0.18 %	0.13 %	0.32 %
Total annual Fund operating expenses(d)	1.44 %	1.19 %	1.05 %	1.00 %	1.19 %
Less: Fee waivers and/or expense reimbursements(e)	(0.30 %)	(0.30 %)	(0.30 %)	(0.30 %)	(0.30 %)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.14 %	0.89 %	0.75 %	0.70 %	0.89 %

(a)

(b)

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

(c)

Management fees include an advisory fee of 0.82% and administrative services fee of 0.05%. As a result of combining those fees as management fees, other expenses do not include administrative services fee.

(d)

(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 1.14% for Class A, 0.89% for Class Inst, 0.75% for Class Inst2, 0.70% for Class Inst3 and 0.89% 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

■

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 Expenses table above.

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$685	$947	$1,261	$2,150
Class Inst (whether or not shares are redeemed)	$91	$317	$595	$1,388
Class Inst2 (whether or not shares are redeemed)	$77	$273	$520	$1,227
Class Inst3 (whether or not shares are redeemed)	$72	$257	$492	$1,169
Class S (whether or not shares are redeemed)	$91	$317	$595	$1,388

The rest of the section remains the same.

Supplement dated March 3, 2025

to the Prospectus and Summary Prospectus, each as supplemented, of the following fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Thermostat FundSM	5/1/2024

Effective immediately (unless a different date is otherwise noted), the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

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(d)	0.10 %	0.10 %	0.10 %	0.10 %	0.10 %	0.10 %
Distribution and/or service (12b-1) fees	0.25 %	1.00 %	0.00 %	0.00 %	0.00 %	0.00 %
Other expenses	0.12 %	0.12 %	0.12 %	0.08 %	0.04 %	0.12 %
Acquired fund fees and expenses	0.36 %	0.36 %	0.36 %	0.36 %	0.36 %	0.36 %
Total annual Fund operating expenses(e)	0.83 %	1.58 %	0.58 %	0.54 %	0.50 %	0.58 %

(a)

(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)

Columbia Wanger Asset Management, LLC (the Investment Manager) has contractually agreed to permanently waive administrative service fees. This arrangement may only be amended or terminated with approval from the Fund’s Board of Trustees and the Investment Manager.

(e)

“Total annual Fund operating expenses” include acquired fund (Portfolio Fund) fees and expenses (expenses the Fund incurs indirectly through its investments in other funds) 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 Portfolio Fund (acquired fund) fees and expenses.

Example

■

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 Expenses table above.

Class C shares’ 10-year cost examples below reflect the Class C shares' 8-year conversion policy. 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)	$655	$825	$1,009	$1,541
Class C (assuming redemption of all shares at the end of the period)	$261	$499	$860	$1,677
Class C (assuming no redemption of shares)	$161	$499	$860	$1,677
Class Inst (whether or not shares are redeemed)	$59	$186	$324	$726
Class Inst2 (whether or not shares are redeemed)	$55	$173	$302	$677
Class Inst3 (whether or not shares are redeemed)	$51	$160	$280	$628

	1 year	3 years	5 years	10 years
Class S (whether or not shares are redeemed)	$59	$186	$324	$726

The rest of the section remains the same.

S000009184 [Member]

rr_RiskReturnAbstract

rr_SupplementToProspectusTextBlock

Supplement dated March 3, 2025

to the Prospectus and Summary Prospectus, each as supplemented, of the following fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Acorn® Fund	5/1/2024

Effective immediately (unless a different date is otherwise noted), the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

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(d)	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(d)	0.13 %	0.13 %	0.13 %	0.09 %	0.05 %	0.13 %
Total annual Fund operating expenses(e)	1.10 %	1.85 %	0.85 %	0.81 %	0.77 %	0.85 %
Less: Fee waivers and/or expense reimbursements(f)	(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)

(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)

(e)

(f)

Example

■

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 Expenses table above.

	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

The rest of the section remains the same.

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_OperatingExpensesCaption

Annual Fund Operating Expenses(c)(expenses that you pay each year as a percentage of the value of your investment)

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2027

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

rr_ExpensesRestatedToReflectCurrent

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

rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees

rr_ExpenseExampleHeading

Example

S000009184 [Member] | C000024954 [Member]

rr_ExpenseExampleNarrativeTextBlock

■

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 Expenses table above.

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

rr_ManagementFeesOverAssets

0.72%

^[2],[3]

rr_DistributionAndService12b1FeesOverAssets

0.25%

^[2]

rr_OtherExpensesOverAssets

0.13%

^[2],[3]

rr_ExpensesOverAssets

1.10%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.03%)

^[2],[5]

rr_NetExpensesOverAssets

1.07%

^[2]

rr_ExpensesDeferredChargesTextBlock

rr_ExpenseExampleYear01

$ 678

rr_ExpenseExampleYear03

899

rr_ExpenseExampleYear05

1,141

rr_ExpenseExampleYear10

1,833

rr_ExpenseExampleNoRedemptionYear01

678

rr_ExpenseExampleNoRedemptionYear03

899

rr_ExpenseExampleNoRedemptionYear05

1,141

S000009184 [Member] | C000024956 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,833

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[6]

rr_ManagementFeesOverAssets

0.72%

^[2],[3]

rr_DistributionAndService12b1FeesOverAssets

1.00%

^[2]

rr_OtherExpensesOverAssets

0.13%

^[2],[3]

rr_ExpensesOverAssets

1.85%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.03%)

^[2],[5]

rr_NetExpensesOverAssets

1.82%

^[2]

rr_ExpensesDeferredChargesTextBlock

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

rr_ExpenseExampleYear01

$ 285

rr_ExpenseExampleYear03

576

rr_ExpenseExampleYear05

995

rr_ExpenseExampleYear10

1,968

rr_ExpenseExampleNoRedemptionYear01

185

rr_ExpenseExampleNoRedemptionYear03

576

rr_ExpenseExampleNoRedemptionYear05

995

S000009184 [Member] | C000024957 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,968

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.72%

^[2],[3]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.13%

^[2],[3]

rr_ExpensesOverAssets

0.85%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.03%)

^[2],[5]

rr_NetExpensesOverAssets

0.82%

^[2]

rr_ExpenseExampleYear01

$ 84

rr_ExpenseExampleYear03

265

rr_ExpenseExampleYear05

465

rr_ExpenseExampleYear10

1,043

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

265

rr_ExpenseExampleNoRedemptionYear05

465

S000009184 [Member] | C000122736 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,043

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.72%

^[2],[3]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.09%

^[2],[3]

rr_ExpensesOverAssets

0.81%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.03%)

^[2],[5]

rr_NetExpensesOverAssets

0.78%

^[2]

rr_ExpenseExampleYear01

$ 80

rr_ExpenseExampleYear03

252

rr_ExpenseExampleYear05

444

rr_ExpenseExampleYear10

996

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

252

rr_ExpenseExampleNoRedemptionYear05

444

S000009184 [Member] | C000122737 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 996

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.72%

^[2],[3]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.05%

^[2],[3]

rr_ExpensesOverAssets

0.77%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.03%)

^[2],[5]

rr_NetExpensesOverAssets

0.74%

^[2]

rr_ExpenseExampleYear01

$ 76

rr_ExpenseExampleYear03

240

rr_ExpenseExampleYear05

422

rr_ExpenseExampleYear10

948

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

240

rr_ExpenseExampleNoRedemptionYear05

422

S000009184 [Member] | C000251059 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 948

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.72%

^[2],[3]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.13%

^[2],[3]

rr_ExpensesOverAssets

0.85%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.03%)

^[2],[5]

rr_NetExpensesOverAssets

0.82%

^[2]

rr_ExpenseExampleYear01

$ 84

rr_ExpenseExampleYear03

265

rr_ExpenseExampleYear05

465

rr_ExpenseExampleYear10

1,043

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

265

rr_ExpenseExampleNoRedemptionYear05

465

rr_ExpenseExampleNoRedemptionYear10

$ 1,043

S000033621 [Member]

rr_RiskReturnAbstract

rr_SupplementToProspectusTextBlock

Supplement dated March 3, 2025

to the Prospectus and Summary Prospectus, each as supplemented, of the following fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Acorn European FundSM	5/1/2024

Effective immediately (unless a different date is otherwise noted), the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

Shareholder Fees (fees paid directly from your investment)
	Class A	Class Inst
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75 %	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)	None

Annual Fund Operating Expenses(b) (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Inst
Management fees(c)	0.97 %	0.97 %
Distribution and/or service (12b-1) fees	0.25 %	0.00 %
Other expenses(c)	0.39 %	0.39 %
Total annual Fund operating expenses(d)	1.61 %	1.36 %
Fee waivers and/or expense reimbursements(e)	(0.24 %)	(0.24 %)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.37 %	1.12 %

(a)

(b)

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

(c)

(d)

(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 1.37% for Class A and 1.12% for Class Inst. 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

■

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 Expenses table above.

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$706	$1,008	$1,357	$2,337
Class Inst (whether or not shares are redeemed)	$114	$382	$698	$1,592

The rest of the section remains the same.

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_OperatingExpensesCaption

Annual Fund Operating Expenses(b)(expenses that you pay each year as a percentage of the value of your investment)

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2027

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

rr_ExpensesRestatedToReflectCurrent

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

rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees

rr_ExpenseExampleHeading

Example

S000033621 [Member] | C000103324 [Member]

rr_ExpenseExampleNarrativeTextBlock

■

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 Expenses table above.

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

rr_ManagementFeesOverAssets

0.97%

^[2],[7]

rr_DistributionAndService12b1FeesOverAssets

0.25%

^[2]

rr_OtherExpensesOverAssets

0.39%

^[2],[7]

rr_ExpensesOverAssets

1.61%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.24%)

^[2],[8]

rr_NetExpensesOverAssets

1.37%

^[2]

rr_ExpensesDeferredChargesTextBlock

rr_ExpenseExampleYear01

$ 706

rr_ExpenseExampleYear03

1,008

rr_ExpenseExampleYear05

1,357

rr_ExpenseExampleYear10

2,337

rr_ExpenseExampleNoRedemptionYear01

706

rr_ExpenseExampleNoRedemptionYear03

1,008

rr_ExpenseExampleNoRedemptionYear05

1,357

S000033621 [Member] | C000103327 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 2,337

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.97%

^[2],[7]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.39%

^[2],[7]

rr_ExpensesOverAssets

1.36%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.24%)

^[2],[8]

rr_NetExpensesOverAssets

1.12%

^[2]

rr_ExpenseExampleYear01

$ 114

rr_ExpenseExampleYear03

382

rr_ExpenseExampleYear05

698

rr_ExpenseExampleYear10

1,592

rr_ExpenseExampleNoRedemptionYear01

114

rr_ExpenseExampleNoRedemptionYear03

382

rr_ExpenseExampleNoRedemptionYear05

698

rr_ExpenseExampleNoRedemptionYear10

$ 1,592

S000009185 [Member]

rr_RiskReturnAbstract

rr_SupplementToProspectusTextBlock

Supplement dated March 3, 2025

to the Prospectus and Summary Prospectus, each as supplemented, of the following fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Acorn International®	5/1/2024

Effective immediately (unless a different date is otherwise noted), the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

Shareholder Fees (fees paid directly from your investment)
	Class A	Classes Inst, Inst2, Inst3 and S
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75 %	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)	None

Annual Fund Operating Expenses(b) (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Inst	Class Inst2	Class Inst3	Class S
Management fees(c)	0.85 %	0.85 %	0.85 %	0.85 %	0.85 %
Distribution and/or service (12b-1) fees	0.25 %	0.00 %	0.00 %	0.00 %	0.00 %
Other expenses(c)	0.20 %	0.20 %	0.13 %	0.09 %	0.20 %
Total annual Fund operating expenses(d)	1.30 %	1.05 %	0.98 %	0.94 %	1.05 %
Less: Fee waivers and/or expense reimbursements(e)	(0.08 %)	(0.08 %)	(0.09 %)	(0.10 %)	(0.08 %)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.22 %	0.97 %	0.89 %	0.84 %	0.97 %

(a)

(b)

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

(c)

(d)

(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 1.22% for Class A, 0.97% for Class Inst, 0.89% for Class Inst2, 0.84% for Class Inst3 and 0.97% 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

■

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 Expenses table above.

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$692	$948	$1,232	$2,039
Class Inst (whether or not shares are redeemed)	$99	$318	$563	$1,268
Class Inst2 (whether or not shares are redeemed)	$91	$294	$524	$1,185
Class Inst3 (whether or not shares are redeemed)	$86	$279	$500	$1,136
Class S (whether or not shares are redeemed)	$99	$318	$563	$1,268

The rest of the section remains the same.

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_OperatingExpensesCaption

Annual Fund Operating Expenses(b)(expenses that you pay each year as a percentage of the value of your investment)

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2027

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

rr_ExpensesRestatedToReflectCurrent

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

rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees

rr_ExpenseExampleHeading

Example

S000009185 [Member] | C000024958 [Member]

rr_ExpenseExampleNarrativeTextBlock

■

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 Expenses table above.

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

rr_ManagementFeesOverAssets

0.85%

^[2],[9]

rr_DistributionAndService12b1FeesOverAssets

0.25%

^[2]

rr_OtherExpensesOverAssets

0.20%

^[2],[9]

rr_ExpensesOverAssets

1.30%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.08%)

^[2],[10]

rr_NetExpensesOverAssets

1.22%

^[2]

rr_ExpensesDeferredChargesTextBlock

rr_ExpenseExampleYear01

$ 692

rr_ExpenseExampleYear03

948

rr_ExpenseExampleYear05

1,232

rr_ExpenseExampleYear10

2,039

rr_ExpenseExampleNoRedemptionYear01

692

rr_ExpenseExampleNoRedemptionYear03

948

rr_ExpenseExampleNoRedemptionYear05

1,232

S000009185 [Member] | C000024961 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 2,039

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.85%

^[2],[9]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.20%

^[2],[9]

rr_ExpensesOverAssets

1.05%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.08%)

^[2],[10]

rr_NetExpensesOverAssets

0.97%

^[2]

rr_ExpenseExampleYear01

$ 99

rr_ExpenseExampleYear03

318

rr_ExpenseExampleYear05

563

rr_ExpenseExampleYear10

1,268

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

318

rr_ExpenseExampleNoRedemptionYear05

563

S000009185 [Member] | C000097733 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,268

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.85%

^[2],[9]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.13%

^[2],[9]

rr_ExpensesOverAssets

0.98%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.09%)

^[2],[10]

rr_NetExpensesOverAssets

0.89%

^[2]

rr_ExpenseExampleYear01

$ 91

rr_ExpenseExampleYear03

294

rr_ExpenseExampleYear05

524

rr_ExpenseExampleYear10

1,185

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

294

rr_ExpenseExampleNoRedemptionYear05

524

S000009185 [Member] | C000122739 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,185

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.85%

^[2],[9]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.09%

^[2],[9]

rr_ExpensesOverAssets

0.94%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.10%)

^[2],[10]

rr_NetExpensesOverAssets

0.84%

^[2]

rr_ExpenseExampleYear01

$ 86

rr_ExpenseExampleYear03

279

rr_ExpenseExampleYear05

500

rr_ExpenseExampleYear10

1,136

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

279

rr_ExpenseExampleNoRedemptionYear05

500

S000009185 [Member] | C000251060 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,136

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.85%

^[2],[9]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.20%

^[2],[9]

rr_ExpensesOverAssets

1.05%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.08%)

^[2],[10]

rr_NetExpensesOverAssets

0.97%

^[2]

rr_ExpenseExampleYear01

$ 99

rr_ExpenseExampleYear03

318

rr_ExpenseExampleYear05

563

rr_ExpenseExampleYear10

1,268

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

318

rr_ExpenseExampleNoRedemptionYear05

563

rr_ExpenseExampleNoRedemptionYear10

$ 1,268

S000009188 [Member]

rr_RiskReturnAbstract

rr_SupplementToProspectusTextBlock

Supplement dated March 3, 2025

to the Prospectus and Summary Prospectus, each as supplemented, of the following fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Acorn International SelectSM	5/1/2024

Effective immediately (unless a different date is otherwise noted), the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

Shareholder Fees (fees paid directly from your investment)
	Class A	Classes Inst, Inst2, Inst3 and S
Maximum sales charge (load) imposed on purchases (as a % of offering price)	5.75 %	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)	None

Annual Fund Operating Expenses(b) (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Inst	Class Inst2	Class Inst3	Class S
Management fees(c)	0.87 %	0.87 %	0.87 %	0.87 %	0.87 %
Distribution and/or service (12b-1) fees	0.25 %	0.00 %	0.00 %	0.00 %	0.00 %
Other expenses(c)	0.32 %	0.32 %	0.18 %	0.13 %	0.32 %
Total annual Fund operating expenses(d)	1.44 %	1.19 %	1.05 %	1.00 %	1.19 %
Less: Fee waivers and/or expense reimbursements(e)	(0.30 %)	(0.30 %)	(0.30 %)	(0.30 %)	(0.30 %)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	1.14 %	0.89 %	0.75 %	0.70 %	0.89 %

(a)

(b)

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

(c)

(d)

(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 1.14% for Class A, 0.89% for Class Inst, 0.75% for Class Inst2, 0.70% for Class Inst3 and 0.89% 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

■

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 Expenses table above.

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$685	$947	$1,261	$2,150
Class Inst (whether or not shares are redeemed)	$91	$317	$595	$1,388
Class Inst2 (whether or not shares are redeemed)	$77	$273	$520	$1,227
Class Inst3 (whether or not shares are redeemed)	$72	$257	$492	$1,169
Class S (whether or not shares are redeemed)	$91	$317	$595	$1,388

The rest of the section remains the same.

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_OperatingExpensesCaption

Annual Fund Operating Expenses(b)(expenses that you pay each year as a percentage of the value of your investment)

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

April 30, 2027

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

rr_ExpensesRestatedToReflectCurrent

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

rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees

rr_ExpenseExampleHeading

Example

S000009188 [Member] | C000024970 [Member]

rr_ExpenseExampleNarrativeTextBlock

■

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 Expenses table above.

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

rr_ManagementFeesOverAssets

0.87%

^[2],[11]

rr_DistributionAndService12b1FeesOverAssets

0.25%

^[2]

rr_OtherExpensesOverAssets

0.32%

^[2],[11]

rr_ExpensesOverAssets

1.44%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.30%)

^[2],[12]

rr_NetExpensesOverAssets

1.14%

^[2]

rr_ExpensesDeferredChargesTextBlock

rr_ExpenseExampleYear01

$ 685

rr_ExpenseExampleYear03

947

rr_ExpenseExampleYear05

1,261

rr_ExpenseExampleYear10

2,150

rr_ExpenseExampleNoRedemptionYear01

685

rr_ExpenseExampleNoRedemptionYear03

947

rr_ExpenseExampleNoRedemptionYear05

1,261

S000009188 [Member] | C000024973 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 2,150

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.87%

^[2],[11]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.32%

^[2],[11]

rr_ExpensesOverAssets

1.19%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.30%)

^[2],[12]

rr_NetExpensesOverAssets

0.89%

^[2]

rr_ExpenseExampleYear01

$ 91

rr_ExpenseExampleYear03

317

rr_ExpenseExampleYear05

595

rr_ExpenseExampleYear10

1,388

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

317

rr_ExpenseExampleNoRedemptionYear05

595

S000009188 [Member] | C000122746 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,388

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.87%

^[2],[11]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.18%

^[2],[11]

rr_ExpensesOverAssets

1.05%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.30%)

^[2],[12]

rr_NetExpensesOverAssets

0.75%

^[2]

rr_ExpenseExampleYear01

$ 77

rr_ExpenseExampleYear03

273

rr_ExpenseExampleYear05

520

rr_ExpenseExampleYear10

1,227

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

273

rr_ExpenseExampleNoRedemptionYear05

520

S000009188 [Member] | C000122747 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,227

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.87%

^[2],[11]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.13%

^[2],[11]

rr_ExpensesOverAssets

1.00%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.30%)

^[2],[12]

rr_NetExpensesOverAssets

0.70%

^[2]

rr_ExpenseExampleYear01

$ 72

rr_ExpenseExampleYear03

257

rr_ExpenseExampleYear05

492

rr_ExpenseExampleYear10

1,169

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

257

rr_ExpenseExampleNoRedemptionYear05

492

S000009188 [Member] | C000251061 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,169

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.87%

^[2],[11]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.32%

^[2],[11]

rr_ExpensesOverAssets

1.19%

^[2],[4]

Total annual Fund operating expenses after fee waivers and/or expense reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.30%)

^[2],[12]

rr_NetExpensesOverAssets

0.89%

^[2]

rr_ExpenseExampleYear01

$ 91

rr_ExpenseExampleYear03

317

rr_ExpenseExampleYear05

595

rr_ExpenseExampleYear10

1,388

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

317

rr_ExpenseExampleNoRedemptionYear05

595

rr_ExpenseExampleNoRedemptionYear10

$ 1,388

S000009189 [Member]

rr_RiskReturnAbstract

rr_SupplementToProspectusTextBlock

Supplement dated March 3, 2025

to the Prospectus and Summary Prospectus, each as supplemented, of the following fund:

Fund	Prospectus and Summary Prospectus Dated
Columbia Acorn Trust
Columbia Thermostat FundSM	5/1/2024

Effective immediately (unless a different date is otherwise noted), the following changes are hereby made to the Fund's Prospectus and Summary Prospectus.

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(d)	0.10 %	0.10 %	0.10 %	0.10 %	0.10 %	0.10 %
Distribution and/or service (12b-1) fees	0.25 %	1.00 %	0.00 %	0.00 %	0.00 %	0.00 %
Other expenses	0.12 %	0.12 %	0.12 %	0.08 %	0.04 %	0.12 %
Acquired fund fees and expenses	0.36 %	0.36 %	0.36 %	0.36 %	0.36 %	0.36 %
Total annual Fund operating expenses(e)	0.83 %	1.58 %	0.58 %	0.54 %	0.50 %	0.58 %

(a)

(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)

(e)

Example

■

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 Expenses table above.

	1 year	3 years	5 years	10 years
Class A (whether or not shares are redeemed)	$655	$825	$1,009	$1,541
Class C (assuming redemption of all shares at the end of the period)	$261	$499	$860	$1,677
Class C (assuming no redemption of shares)	$161	$499	$860	$1,677
Class Inst (whether or not shares are redeemed)	$59	$186	$324	$726
Class Inst2 (whether or not shares are redeemed)	$55	$173	$302	$677
Class Inst3 (whether or not shares are redeemed)	$51	$160	$280	$628

	1 year	3 years	5 years	10 years
Class S (whether or not shares are redeemed)	$59	$186	$324	$726

The rest of the section remains the same.

rr_ShareholderFeesCaption

Shareholder Fees (fees paid directly from your investment)

rr_OperatingExpensesCaption

Annual Fund Operating Expenses(c)(expenses that you pay each year as a percentage of the value of your investment)

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

rr_ExpensesRestatedToReflectCurrent

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

rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees

rr_ExpenseExampleHeading

Example

S000009189 [Member] | C000024974 [Member]

rr_ExpenseExampleNarrativeTextBlock

■

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 Expenses table above.

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.75%

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[1]

rr_ManagementFeesOverAssets

0.10%

^[2],[13]

rr_DistributionAndService12b1FeesOverAssets

0.25%

^[2]

rr_OtherExpensesOverAssets

0.12%

^[2]

rr_AcquiredFundFeesAndExpensesOverAssets

0.36%

^[2]

rr_ExpensesOverAssets

0.83%

^[2],[14]

rr_ExpensesDeferredChargesTextBlock

rr_ExpenseExampleYear01

$ 655

rr_ExpenseExampleYear03

825

rr_ExpenseExampleYear05

1,009

rr_ExpenseExampleYear10

1,541

rr_ExpenseExampleNoRedemptionYear01

655

rr_ExpenseExampleNoRedemptionYear03

825

rr_ExpenseExampleNoRedemptionYear05

1,009

S000009189 [Member] | C000024976 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,541

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

1.00%

^[6]

rr_ManagementFeesOverAssets

0.10%

^[2],[13]

rr_DistributionAndService12b1FeesOverAssets

1.00%

^[2]

rr_OtherExpensesOverAssets

0.12%

^[2]

rr_AcquiredFundFeesAndExpensesOverAssets

0.36%

^[2]

rr_ExpensesOverAssets

1.58%

^[2],[14]

rr_ExpensesDeferredChargesTextBlock

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

rr_ExpenseExampleYear01

$ 261

rr_ExpenseExampleYear03

499

rr_ExpenseExampleYear05

860

rr_ExpenseExampleYear10

1,677

rr_ExpenseExampleNoRedemptionYear01

161

rr_ExpenseExampleNoRedemptionYear03

499

rr_ExpenseExampleNoRedemptionYear05

860

S000009189 [Member] | C000024977 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 1,677

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.10%

^[2],[13]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.12%

^[2]

rr_AcquiredFundFeesAndExpensesOverAssets

0.36%

^[2]

rr_ExpensesOverAssets

0.58%

^[2],[14]

rr_ExpenseExampleYear01

$ 59

rr_ExpenseExampleYear03

186

rr_ExpenseExampleYear05

324

rr_ExpenseExampleYear10

726

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

186

rr_ExpenseExampleNoRedemptionYear05

324

S000009189 [Member] | C000122750 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 726

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.10%

^[2],[13]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.08%

^[2]

rr_AcquiredFundFeesAndExpensesOverAssets

0.36%

^[2]

rr_ExpensesOverAssets

0.54%

^[2],[14]

rr_ExpenseExampleYear01

$ 55

rr_ExpenseExampleYear03

173

rr_ExpenseExampleYear05

302

rr_ExpenseExampleYear10

677

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

173

rr_ExpenseExampleNoRedemptionYear05

302

S000009189 [Member] | C000122751 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 677

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.10%

^[2],[13]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.04%

^[2]

rr_AcquiredFundFeesAndExpensesOverAssets

0.36%

^[2]

rr_ExpensesOverAssets

0.50%

^[2],[14]

rr_ExpenseExampleYear01

$ 51

rr_ExpenseExampleYear03

160

rr_ExpenseExampleYear05

280

rr_ExpenseExampleYear10

628

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

160

rr_ExpenseExampleNoRedemptionYear05

280

S000009189 [Member] | C000251062 [Member]

rr_ExpenseExampleNoRedemptionYear10

$ 628

Maximum sales charge (load) imposed on purchases (as a % of offering price)

rr_RiskReturnAbstract

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum deferred sales charge (load) imposed on redemptions (as a % of the lower of the original purchase price or current net asset value)

rr_MaximumDeferredSalesChargeOverOther

none

rr_ManagementFeesOverAssets

0.10%

^[2],[13]

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

rr_OtherExpensesOverAssets

0.12%

^[2]

rr_AcquiredFundFeesAndExpensesOverAssets

0.36%

^[2]

rr_ExpensesOverAssets

0.58%

^[2],[14]

rr_ExpenseExampleYear01

$ 59

rr_ExpenseExampleYear03

186

rr_ExpenseExampleYear05

324

rr_ExpenseExampleYear10

726

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

186

rr_ExpenseExampleNoRedemptionYear05

324