Columbia Funds Series Trust I

Summary Prospectus

September 1, 2017

Columbia U.S. Treasury Index Fund

Class		Ticker Symbol
Class A Shares		LUTAX
Class C Shares		LUTCX
Class R5 Shares		CUTRX
Class T Shares*		CTIWX
Class Y Shares		CUTYX
Class Z Shares		IUTIX

* Prior to March 27, 2017, Class T shares were known as Class W shares.

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, statement of additional information and other information about the Fund online at https://www.columbiathreadneedleus.com/resources/literature. You can also 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, 2017, 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 Citi Bond U.S. 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 and hold shares of the Fund. The front-end sales charge applicable to Class T shares is a per-transaction charge, meaning that separate orders will not be aggregated for purposes of calculating the rate of the sales charge payable. An investor transacting in a class of Fund shares without any front-end sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution may be required to pay a commission to the financial intermediary for effecting such transactions. Such commission rates are set by the financial intermediary and are not reflected in the tables or the example below. You may qualify for sales charge waivers. More information about these sales charge waivers is available from your financial intermediary, and can be found in the Choosing a Share Class section beginning on page 18 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)
	Class A	Class C	Class T	Classes R5, Y and Z
Maximum sales charge (load) imposed on purchases (as a % of offering price)	None	None	2.50%	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	1.00% ^(a)	None	None

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
	Class A	Class C	Class R5	Class T	Class Y	Class Z
Management fees	0.40%	0.40%	0.40%	0.40%	0.40%	0.40%
Distribution and/or service (12b-1) fees	0.25%	1.00%	0.00%	0.25%	0.00%	0.00%
Other expenses^(b)	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Total annual Fund operating expenses	0.65%	1.40%	0.40%	0.65%	0.40%	0.40%
Less: Fee waivers and/or expense reimbursements^(c)	(0.20%)	(0.20%)	(0.20%)	(0.20%)	(0.20%)	(0.20%)
Total annual Fund operating expenses after fee waivers and/or expense reimbursements	0.45%	1.20%	0.20%	0.45%	0.20%	0.20%

(a)	This charge applies to redemptions within 12 months after purchase, with certain limited exceptions.
(b)	Other expenses for Class Y shares are based on estimated amounts for the Fund’s current fiscal year.
(c)	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, 2018, 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 0.45% for Class A, 1.20% for Class C, 0.20% for Class R5, 0.45% for Class T, 0.20% for Class Y and 0.20% for Class Z.

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.

1	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)	$ 46	$188	$342	$ 791
Class C (assuming redemption of all shares at the end of the period)	$222	$423	$747	$1,662
Class C (assuming no redemption of shares)	$122	$423	$747	$1,662
Class R5 (whether or not shares are redeemed)	$ 20	$108	$204	$ 486
Class T (whether or not shares are redeemed)	$295	$433	$584	$1,022
Class Y (whether or not shares are redeemed)	$ 20	$108	$204	$ 486
Class Z (whether or not shares are redeemed)	$ 20	$108	$204	$ 486

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 50% of the average value of its portfolio.

Principal Investment Strategies

Under normal circumstances, the Fund invests at least 80% of its net assets (including the amount of any borrowings for investment purposes) in securities that comprise the Citi Bond U.S. 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 Citi 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.

Principal Risks

An investment in the Fund involves risks, including those described 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.

Correlation/Tracking Error Risk. The Fund’s value will generally decline when the performance of 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. The factors that may adversely affect the Fund’s correlation with the Index include the size of the Fund’s portfolio, fees, expenses, transaction costs, income items, valuation methodology, accounting standards, the effectiveness of sampling techniques (if applicable), changes in the Index and disruptions or illiquidity in the markets for the securities or other instruments in which the Fund invests. While the Fund typically seeks to track the performance of the Index by investing all, or substantially all, of its assets in the components of the Index in approximately the same proportion as their weighting in the Index, at times, the Fund may not have investment exposure to all components of the Index, or its weighting of investment exposure to such components may be different from that of the Index. In addition, the Fund may invest in securities or other instruments not included in the Index. The Fund may take or refrain from taking investment positions for various reasons, such as tax efficiency purposes, or to comply with regulatory restrictions, which may negatively affect the Fund’s correlation with the Index. The Fund may also be subject to large movements of assets into and out of the Fund, potentially resulting in the Fund being over- or under-exposed to certain components of the Index and may be impacted by Index reconstitutions and Index rebalancing events. Holding cash balances may prevent the Fund from tracking the Index. In addition, the Fund’s NAV may deviate from the Index if the Fund fair values a portfolio security at a price other than the price used by the Index for that security. The Fund also bears management and other expenses and transaction costs in trading securities or other instruments, which the Index does not bear.

Columbia U.S. Treasury Index Fund

Accordingly, the Fund’s performance will likely fail to match the performance of the Index, after taking expenses into account. Any of these factors could decrease correlation between the performance of the Fund and the Index and may hinder the Fund’s ability to meet its investment objective. 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. Rating agencies assign credit ratings to certain debt instruments to indicate their credit risk. Lower quality or unrated instruments held by the Fund may present increased credit risk as compared to higher-rated instruments. Non-investment grade debt instruments (commonly called “high-yield” or “junk”) 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. If the Fund purchases unrated instruments, or if the ratings of instruments held by the Fund are lowered after purchase, the Fund will depend on analysis of credit risk more heavily than usual.

Interest Rate Risk. Interest rate risk is the risk of losses attributable to changes in interest rates. In general, if prevailing interest rates (which are currently near historic lows) 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 the Fund's shares. In general, the longer the maturity or duration of a debt instrument, the greater its sensitivity to changes in interest rates. Interest rate declines also may increase prepayments of debt obligations, which, in turn, would increase prepayment risk. Similarly, a period of rising interest rates may negatively impact the Fund’s performance. Actions by governments and central banking authorities can result in increases in 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. Market risk refers to the possibility that the market values of securities or other investments that the Fund holds will fall, sometimes rapidly or unpredictably, or fail to rise. An investment in the Fund could lose money over short or long periods.

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.

3	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. Class Y shares of the Fund commenced operations after the periods shown in the table below and, therefore, performance information is not yet available. 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. Prior to March 27, 2017, Class T shares were known as Class W shares and there was no sales charge on Class W shares. Beginning March 27, 2017, the maximum applicable sales charge attributable to Class T shares is 2.50% per transaction. The Fund’s Class T share returns (after applicable sales charges) have been adjusted to reflect the current maximum applicable sales charge of 2.50%.

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 Z shares (adjusted to reflect the higher class-related operating expenses of such classes, where applicable) for periods prior to its inception date. Any share class, such as Class Y shares, that does not have available performance would have annual returns substantially similar to those of Class A shares. 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 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 columbiathreadneedle.com/us.

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	_{4th Quarter 2008}	_8.75%
	_Worst	_{4th Quarter 2016}	_-3.86%

*	Year to Date return as of June 30, 2017: 1.77%

Average Annual Total Returns After Applicable Sales Charges (for periods ended December 31, 2016)

	Share Class Inception Date	1 Year	5 Years	10 Years
Class A	11/25/2002
returns before taxes		0.72%	0.78%	3.54%
returns after taxes on distributions		0.09%	0.02%	2.49%
returns after taxes on distributions and sale of Fund shares		0.45%	0.36%	2.42%
Class C returns before taxes	11/25/2002	-0.97%	0.13%	2.90%
Class R5 returns before taxes	11/08/2012	0.87%	0.98%	3.77%
Class T returns before taxes	06/18/2012	-1.86%	0.19%	3.12%
Class Z returns before taxes	06/04/1991	0.87%	0.99%	3.77%
Citi Bond U.S. Treasury Index (reflects no deductions for fees, expenses or taxes)		1.03%	1.19%	3.93%

Columbia U.S. Treasury Index Fund

Fund Management

Investment Manager: Columbia Management Investment Advisers, LLC

Portfolio Manager		Title		Role with Fund		Managed Fund Since
Alan Erickson, CFA		Portfolio Manager		Portfolio Manager		January 2017

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
investor.columbiathreadneedle.com/us		Columbia Funds, c/o Columbia Management Investment Services Corp. P.O. Box 8081 Boston, MA 02266-8081		Columbia Funds, c/o Columbia Management Investment Services Corp. 30 Dan Road, Suite 8081 Canton, MA 02021-2809		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	For systematic investment plan accounts
Classes A, C & T^(b))	All accounts other than IRAs	$2,000	$100
Classes A, C & T^(b))	IRAs	$1,000	$100
Class R5	All eligible accounts	None	N/A
Class Y	All eligible accounts	$0, $1,000, $2,000 or $1 million depending upon the category of eligible investor	$100 (for certain eligible investors)
Class Z	All eligible accounts	$0, $1,000 or $2,000 depending upon the category of eligible investor	$100

(b)	Class T shares must be purchased through financial intermediaries that, by written agreement with Columbia Management Investment Distributors, Inc., are specifically authorized to sell Class T shares.

There is no minimum additional investment for any share class.

5	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

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

columbiathreadneedle.com/us

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