COLUMBIA FUNDS SERIES TRUST I

Columbia U.S. Treasury Index Fund

Summary Prospectus

September 1, 2026

Class	Ticker Symbol
A	LUTAX
Institutional (Class Inst)	IUTIX
Institutional 2 (Class Inst2)	CUTRX
Institutional 3 (Class Inst3)	CUTYX

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 September 1, 2026, 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 U.S. Treasury Index Fund (the Fund) seeks total return that corresponds to the total return of the FTSE USBIG Treasury Index, before fees and expenses.

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 waivers. More information is available about these sales charge 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 Waivers beginning on page S-1.

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

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class Inst	Class Inst2	Class Inst3
Management fees	0.40 %	0.40 %	0.40 %	0.40 %
Distribution and/or service (12b-1) fees	0.15 %	0.00 %	0.00 %	0.00 %
Other expenses	0.00 %	0.00 %	0.00 %	0.00 %
Total annual Fund operating expenses(a)	0.55 %	0.40 %	0.40 %	0.40 %
Less: Fee waivers and/or expense reimbursements(b)	(0.23 %)	(0.23 %)	(0.23 %)	(0.23 %)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	0.32 %	0.17 %	0.17 %	0.17 %

(a)

“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.

(b)

Columbia Management Investment Advisers, LLC 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 August 31, 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 0.32% for Class A, 0.17% for Class Inst, 0.17% for Class Inst2 and 0.17% for Class Inst3. Any differences 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,

■

you redeem all your shares at the end of the period,

■

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.

Columbia U.S. Treasury Index Fund

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 year 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)	$33	$153	$284	$667
Class Inst (whether or not shares are redeemed)	$17	$105	$201	$483
Class Inst2 (whether or not shares are redeemed)	$17	$105	$201	$483
Class Inst3 (whether or not shares are redeemed)	$17	$105	$201	$483

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 44% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in securities that comprise the FTSE USBIG Treasury Index (the Index). The Index is an unmanaged index composed of U.S. Treasury notes and bonds with remaining maturities of at least one year and outstanding principal of at least $5 billion and which are included in the FTSE U.S. Broad Investment-Grade Bond Index. Different securities have different weightings in the Index. Securities in the Index are weighted by market value; that is, the price per bond or note multiplied by the number of bonds or notes outstanding.

In seeking to match the performance of the Index, before fees and expenses, the investment manager attempts to allocate the Fund’s assets among securities in the Index. The Fund will not hold all of the securities in the Index.

The Fund may operate as non-diversified when the Index is non-diversified. A non-diversified fund can invest a greater percentage of its assets in the securities of fewer issuers than can a diversified fund.

Principal Risks

An investment in the Fund involves risks, including Interest Rate Risk, Market Risk, Passive Investment Risk, Correlation/Tracking Error Risk, U.S. Government Obligations Risk and Credit 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.

Correlation/Tracking Error Risk. The Fund’s value will generally decline when the performance of the securities within the Index declines. A number of factors may affect the Fund’s ability to achieve a high degree of correlation with the Index, and there is no guarantee that the Fund will achieve a high degree of correlation. Failure to achieve a high degree of correlation may prevent the Fund from achieving its investment objective. In addition, the Fund bears management and other expenses and transaction costs in trading securities or other instruments, which the Index does not bear. The Fund, unlike the Index, is subject to regulatory requirements that can limit the Fund’s investments relative to what the Index can hold. Accordingly, the Fund's performance will likely fail to match the performance of the Index, after taking expenses into account, as well as regulatory limitations. It is not possible to invest directly in an index.

Credit Risk. Credit risk is the risk that the value of debt instruments may decline if the issuer thereof defaults or otherwise becomes unable or unwilling, or is perceived to be unable or unwilling, to honor its financial obligations, such as making payments to the Fund when due. Credit rating agencies, such as S&P Global Ratings, Moody’s Investors Service, Inc. (Moody’s Ratings), Fitch Ratings, Inc. (Fitch), Morningstar DBRS (DBRS) and Kroll Bond Rating Agency, LLC (KBRA), assign credit ratings to certain debt instruments to indicate their credit risk. A rating downgrade by such agencies can negatively impact the value of such instruments. Lower-rated or unrated instruments held by

Columbia U.S. Treasury Index Fund

the Fund may present increased credit risk as compared to higher-rated instruments. Non-investment grade debt instruments may be subject to greater price fluctuations and are more likely to experience a default than investment grade debt instruments and therefore may expose the Fund to increased credit risk.

Fixed Income Instruments Risk. The Fund is subject to the general risks and considerations associated with investing in debt securities, including the risk that issuers will fail to make timely payments of principal or interest or default altogether. Lower-rated securities in which the Fund may invest may be more volatile and may decline more in price in response to negative issuer developments or general economic news than higher rated securities. In addition, as interest rates rise, the Fund’s investments typically will lose value.

Interest Rate Risk. Interest rate risk is the risk of losses attributable to changes in interest rates. In general, if interest rates rise, the values of debt instruments tend to fall, and if interest rates fall, the values of debt instruments tend to rise. Changes in the value of a debt instrument usually will not affect the amount of income the Fund receives from it but will generally affect the value of your investment in the Fund. Changes in interest rates may also affect the liquidity of the Fund’s investments in debt instruments. In general, the longer the maturity or duration of a debt instrument, the greater its sensitivity to changes in interest rates. For example, a three-year duration means a bond is expected to decrease in value by 3% if interest rates rise 1% and increase in value by 3% if interest rates fall 1%. Interest rate declines also may increase prepayments of debt obligations, which, in turn, would increase prepayment risk. The Fund is subject to the risk that the income generated by its investments may not keep pace with inflation. Actions by governments and central banking authorities can result in increases or decreases in interest rates. Higher periods of inflation could lead such authorities to raise interest rates. Such actions may negatively affect the value of debt instruments held by the Fund, resulting in a negative impact on the Fund's performance and NAV. Any interest rate increases could cause the value of the Fund’s investments in debt instruments to decrease. Rising interest rates may prompt redemptions from the Fund, which may force the Fund to sell investments at a time when it is not advantageous to do so, which could result in losses.

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.

Non-Diversified Fund Risk. The Fund is passively managed to track an unaffiliated index, and the Fund may hold a non-diversified portfolio to the extent that its index’s holdings represent a non-diversified portfolio. When holding a non-diversified portfolio, it may invest a greater percentage of its total assets in the securities of fewer issuers than a “diversified” fund. This increases the risk that a change in the value of any one investment held by the Fund could affect the overall value of the Fund more than it would affect that of a diversified fund holding a greater number of investments. Accordingly, the Fund's value will likely be more volatile than the value of a more diversified fund.

Passive Investment Risk. The Fund is not actively managed and may be affected by a general decline in market segments related to its Index’s investment exposures. The Fund invests in securities or instruments included in, or believed by the portfolio manager to be representative of, the Index regardless of their investment merits. The Fund does not seek temporary defensive positions when markets decline or appear overvalued.

U.S. Government Obligations Risk. While U.S. Treasury obligations are backed by the “full faith and credit” of the U.S. Government, such securities are nonetheless subject to credit risk (i.e., the risk that the U.S. Government may be, or be perceived to be, unable or unwilling to honor its financial obligations, such as making payments). Securities issued or guaranteed by federal agencies or authorities and U.S. Government-sponsored instrumentalities or enterprises may or may not be backed by the full faith and credit of the U.S. Government.

Columbia U.S. Treasury Index Fund

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 A share performance has varied for each full calendar year shown. The table below the bar chart compares the Fund’s returns (after applicable sales charges shown in the Shareholder Fees table in this prospectus) 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.

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 for periods prior to its inception date.

Except for differences in annual returns resulting from differences in expenses and sales charges (where applicable), the 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 A 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	1st Quarter 2020	8.03%
	Worst	1st Quarter 2022	-5.47%

Year to Date return as of June 30, 2026: 0.26%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2025)

	Share Class Inception Date	1 Year	5 Years	10 Years
Class A	11/25/2002
returns before taxes		5.86%	-1.30%	1.03%
returns after taxes on distributions		4.38%	-2.24%	0.19%
returns after taxes on distributions and sale of Fund shares		3.45%	-1.38%	0.44%
Class Inst returns before taxes	06/04/1991	6.02%	-1.13%	1.19%
Class Inst2 returns before taxes	11/08/2012	6.02%	-1.14%	1.19%
Class Inst3 returns before taxes	03/01/2017	6.00%	-1.15%	1.18%
FTSE USBIG Treasury Index (reflects no deductions for fees, expenses or taxes)		6.30%	-0.97%	1.36%
Bloomberg U.S. Aggregate Bond Index (reflects no deductions for fees, expenses or taxes)		7.30%	-0.36%	2.01%

Columbia U.S. Treasury Index Fund

Fund Management

Investment Manager: Columbia Management Investment Advisers, LLC

Portfolio Management	Title	Role with Fund	Managed Fund Since
David Janssen, CFA	Portfolio Manager	Portfolio Manager	2024

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
Class A	All accounts other than IRAs	$2,000	$100
Class A	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 Shares section of the prospectus. There is no minimum additional investment for any share class.

Columbia U.S. Treasury Index Fund

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 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 Management Investment Advisers, 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 U.S. Treasury Index Fund