Columbia Funds Series Trust I

Supplement dated December 20, 2017

to the Prospectus, as supplemented, of the following fund:

Fund	Prospectus Dated
Columbia Funds Series Trust I
Columbia Diversified Real Return Fund	6/1/2017

Columbia Emerging Markets Consumer ETF, Columbia Large Cap Index Fund, Columbia Mid Cap Index Fund, Columbia Small Cap Index Fund, Columbia Sustainable U.S. Equity Income ETF and Columbia U.S. Treasury Index Fund are added as underlying funds. Accordingly, the following is added to Appendix A — Underlying Funds — Investment Objectives and Strategies:

Columbia Emerging Markets Consumer ETF

Columbia Emerging Markets Consumer ETF (the Fund) seeks investment results that correspond (before fees and expenses) to the price and yield performance of the Dow Jones Emerging Markets Consumer Titans 30TM Index (the Index).

The Fund is an exchange-traded fund (ETF). The Fund seeks to achieve its investment objective by attempting to replicate the performance of the Index through investments in equity securities, including, but not limited to, common shares traded on local exchanges, American Depositary Receipts (ADRs) and Global Depositary Receipts (GDRs). The Fund may invest a portion of its assets through a wholly owned subsidiary (the Subsidiary) located in the Republic of Mauritius (Mauritius), which in turn invests at least 90% of its assets in Indian securities. This investment structure enables the Fund to obtain benefits under a tax treaty between Mauritius and India. The Fund may also invest directly in common shares traded on local exchanges, ADRs and GDRs.

Columbia Large Cap Index Fund

Columbia Large Cap Index Fund (the Fund) seeks total return before fees and expenses that corresponds to the total return of the Standard & Poor’s (S&P) 500^® Index.

Under normal circumstances, the Fund invests at least 80% of its net assets (including the amount of any borrowings for investment purposes) in common stocks that comprise the S&P 500 Index (the Index). The Fund may invest in derivatives, including futures (including equity index futures), for cash equitization purposes.

Different common stocks have different weightings in the Index, depending on the amount of stock outstanding and the stock’s current price. In seeking to match the performance of the Index, Columbia Management Investment Advisers, LLC (the Investment Manager) attempts to allocate the Fund’s assets among common stocks in approximately the same weightings as the Index. This is referred to as a passive or indexing approach to investing. The Fund may buy shares of Ameriprise Financial, Inc., an affiliate of the Fund’s investment manager, which is currently included in the Index, subject to certain restrictions.

The Fund attempts to achieve at least a 95% correlation between the performance of the Index and the Fund’s investment results, before fees and expenses.

Columbia Mid Cap Index Fund

Columbia Mid Cap Index Fund (the Fund) seeks total return before fees and expenses that corresponds to the total return of the Standard & Poor’s (S&P) MidCap 400^® Index.

Under normal circumstances, the Fund invests at least 80% of its net assets (including the amount of any borrowings for investment purposes) in common stocks that comprise the S&P MidCap 400 Index (the Index). The Fund also may invest in real estate investment trusts.

The Fund may invest in derivatives, including futures (including equity index futures), for cash equitization purposes.

Different common stocks have different weightings in the Index, depending on the amount of stock outstanding and the stock’s current price. In seeking to match the performance of the Index, Columbia Management Investment Advisers, LLC (the Investment Manager) attempts to allocate the Fund’s assets among common stocks in approximately the same weightings as the Index. This is referred to as a passive or indexing approach to investing. As a result of the Fund’s indexing approach to investing, the Fund will typically emphasize within the portfolio those economic sectors emphasized by the Index, such as the financial services sector.

The Fund attempts to achieve at least a 95% correlation between the performance of the Index and the Fund’s investment results, before fees and expenses.

Columbia Small Cap Index Fund

Columbia Small Cap Index Fund (the Fund) seeks total return before fees and expenses that corresponds to the total return of the Standard & Poor’s (S&P) SmallCap 600^®Index.

Under normal circumstances, the Fund invests at least 80% of its net assets (including the amount of any borrowings for investment purposes) in common stocks that comprise the S&P SmallCap 600 Index (the Index). The Fund may invest in derivatives, including futures (including equity index futures), for cash equitization purposes.

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approximately the same weightings as the Index. This is referred to as a passive or indexing approach to investing. As a result of the Fund’s indexing approach to investing, the Fund will typically emphasize within the portfolio those economic sectors emphasized by the Index, such as the financial services sector.

The Fund attempts to achieve at least a 95% correlation between the performance of the Index and the Fund’s investment results, before fees and expenses.

Columbia Sustainable U.S. Equity Income ETF

Columbia Sustainable U.S. Equity Income ETF (the Fund) seeks investment results that, before fees and expenses, closely correspond to the performance of the Beta Advantage® Sustainable U.S. Equity Income 100 Index (the Index).

The Fund uses an indexing investment approach that seeks to replicate the performance of the Index. The Fund invests at least 80% of its assets in the component securities of the Index. The Index is owned and calculated by MSCI Inc. (MSCI or the Index Provider). The Index was developed by MSCI with input from Columbia Management Investment Advisers, LLC (the Investment Manager). The Index, which typically holds common stocks, was constructed to provide exposure to U.S. large- and mid-cap companies that are believed to offer sustainable levels of income, as well as total return opportunity.

Columbia U.S. Treasury Index Fund

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.

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.

The rest of the section remains the same.

The following is added to Appendix B - Underlying Funds - Principal Risks:

Authorized Participant Concentration Risk. Only an Authorized Participant may engage in creation or redemption transactions directly with the Fund. The Fund has a limited number of institutions that may act as Authorized Participants, none of which are or will be obligated to engage in creation or redemption transactions. To the extent that these institutions exit the business or are unable or unwilling to proceed with creation and/or redemption orders with respect to the Fund and no other Authorized Participant is able or willing to step forward to create or redeem Creation Units, Fund shares may trade at a discount to NAV and possibly face trading halts and/or delisting from the Exchange. This risk is heightened in times of market stress, including at both the Fund share level and at the Fund holdings level.

Concentration Risk. The Fund will concentrate its investments in companies conducting business in a related group of industries within a sector(s) to approximately the same extent as the Index. Companies in the same sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that sector than funds that invest more broadly. Generally, the more broadly a fund diversifies its investments, the more it spreads risk and potentially reduces the risks of loss and volatility.

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 detract from the Fund’s ability to track 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. 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.

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Depositary Receipts Risk. Depositary receipts are receipts issued by a bank or trust company reflecting ownership of underlying securities issued by foreign companies. Some foreign securities are traded in the form of American Depositary Receipts and/or Global Depositary Receipts. Depositary receipts involve risks similar to the risks associated with investments in foreign securities, including those associated with investing in the particular country of an issuer, which may be related to the particular political, regulatory, economic, social and other conditions or events, including, for example, military confrontations, war and terrorism, occurring in the country and fluctuations in its currency, as well as market risk tied to the underlying foreign company. In addition, depositary receipt holders may have limited voting rights, may not have the same rights afforded typical company stockholders in the event of a corporate action such as an acquisition, merger or rights offering and may experience difficulty in receiving company stockholder communications. There is no guarantee that a financial institution will continue to sponsor depositary receipts, or that the depositary receipts will continue to trade on an exchange, either of which could adversely affect the liquidity, availability and pricing of the depositary receipt. Changes in foreign currency exchange rates will affect the value of depositary receipts and, therefore, may affect the value of the Fund's portfolio. To the extent that the exchange price of a depositary receipt differs from the local price of the underlying security used by the Index, the Fund may be prevented from fully achieving its investment objective of tracking the performance of the Index.

Early Close/Late Close/Trading Halt Risk. An exchange or market may close early, close late or issue trading halts on specific securities, or the ability to buy or sell certain securities may be restricted, which may result in the Fund being unable to buy or sell these securities. In these circumstances, the Fund may be unable to rebalance its portfolio, may be unable to accurately price its investments, may incur substantial trading losses and/or may be prevented from sufficiently tracking the performance of the Index.

Environmental, Social and Governance Investing Risk. The Index’s environmental, social and corporate governance screening may cause the Fund to forgo certain investment opportunities, and/or forgo opportunities to gain exposure to certain industries, sectors, regions, countries and companies that could have benefited the Fund. In addition, the Fund may be required to sell a security when it might otherwise be disadvantageous for it to do so.

Foreign Currency Risk. The performance of the Fund may be materially affected positively or negatively by foreign currency strength or weakness relative to the U.S. dollar, particularly if the Fund invests a significant percentage of its assets in foreign securities or other assets denominated in currencies other than the U.S. dollar.

Fund Shares Liquidity Risk. Although the Fund’s shares are listed on the Exchange, there can be no assurance that an active, liquid or otherwise orderly trading market for shares will be established or maintained by market makers or Authorized Participants, particularly in times of stressed market conditions. In this regard, there is no obligation for market makers to make a market in the Fund’s shares or for Authorized Participants to submit purchase or redemption orders for creation units. Accordingly, if such parties determine not to perform their respective roles, this could, in turn, lead to variances between the market price of the Fund’s shares and the underlying value of those shares. Trading in Fund shares on the Exchange also may be disrupted or even halted due to market conditions or for reasons that, in the view of the Exchange, make trading in Fund shares inadvisable. In addition, trading in Fund shares on the Exchange may be subject to trading halts caused by extraordinary market volatility pursuant to the Exchange “circuit breaker” rules. There also can be no assurance that the requirements of the Exchange necessary to maintain the listing of the Fund’s shares will continue to be met or will remain unchanged.

Geographic Focus Risk. The Fund may be particularly susceptible to economic, political, regulatory or other events or conditions affecting issuers and countries within the specific geographic regions in which the Fund invests. The Fund’s NAV may be more volatile than the NAV of a more geographically diversified fund.

Index Fund Risk. The Fund is an index fund, which means that it seeks to track the performance of the Index by using indexing strategies and, therefore, the Fund would not necessarily sell a security because the security’s issuer was in financial trouble or defaulted, or whose credit rating was downgraded, unless that security was removed from the Index. The decision of whether to remove a security from the Index is made by an independent index provider who is not affiliated with the Fund or the Investment Manager.

Index Methodology Risk. The Fund seeks performance that corresponds to the performance of the Index. There is no guarantee or assurance that the Index will achieve high, or even positive, returns. The Index may underperform more traditional indices. The Fund could lose value while other indices or measures of market performance increase in value or performance. In addition, the Fund may be subject to the risk that the index provider may not follow its stated methodology for construction of the Index and/or achieve the index provider’s intended performance objective. Errors may result in a negative performance impact to the Fund and its shareholders.

Limitations of Intraday Indicative Value (IIV) Risk. The Exchange intends to disseminate the approximate per share value of the Fund’s published basket of portfolio securities every 15 seconds (the ‘‘intraday indicative value’’ or ‘‘IIV’’). The IIV should not be viewed as a ‘‘real-time’’ update of the NAV per share of the Fund because (i) the IIV may not be calculated in the same manner as the NAV, which is computed once a day, generally at the end of the business day, (ii) the calculation of NAV may be subject to fair valuation at different prices than those used in the calculations of the IIV, (iii) unlike the calculation of NAV, the IIV does not take into account Fund expenses, and (iv) the IIV is based on the published basket of portfolio securities and not on the Fund’s actual holdings. The IIV calculations are based on local market prices and may not reflect events that occur subsequent to the local market’s close, which could affect premiums and discounts between the IIV and the market price of the Fund’s shares. For example, if the Fund fair values portfolio securities, the Fund’s NAV may deviate from the approximate per share value of the Fund’s published basket of portfolio securities (i.e., the IIV), which could result in the market prices for Fund shares deviating from NAV. The Fund, the Investment Manager and their affiliates are not involved in, or responsible for, any aspect of the calculation or dissemination of the Fund’s IIV, and the Fund, the Investment Manager and their affiliates do not make any warranty as to the accuracy of these calculations.

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Market Price Relative to NAV Risk. Shares of the Fund may trade at prices that vary from Fund NAV. Shares of the Fund are listed for trading on the Exchange and are bought and sold in the secondary market at market prices that may differ, in some cases significantly, from their NAV. The NAV of the Fund will generally fluctuate with changes in the market value of the Fund’s holdings. The market prices of shares, however, will generally fluctuate in response to changes in NAV, as well as the relative supply of, and demand for, Fund shares on the Exchange. The Investment Manager cannot predict whether Fund shares will trade below, at or above their NAV. Price differences may result because of, among other factors, supply and demand forces in the secondary trading market for Fund shares. It is expected that these forces generally will be closely related to, but not identical to, the same forces influencing the prices of the Fund’s holdings. In this connection, if a shareholder purchases Fund shares at a time when the market price is at a premium to the NAV or sells shares at a time when the market price is at a discount to the NAV, the shareholder may sustain losses. Different investment strategies or techniques, including those intended to be defensive in nature, including, as examples, stop loss orders to sell an ETF’s shares in the secondary market during negative market events or conditions, such as a “flash crash” or other market disruptions may not work as intended and may produce significant losses to investors. Investors should consult their financial intermediary prior to using any such investment strategies or techniques, or before investing in the Fund.

Mauritius Subsidiary. General anti-avoidance rules (GAAR) have been enacted in India, the application of which could result in the Subsidiary not being entitled to the benefits of a tax treaty between Mauritius and India. GAAR seeks to curb tax evasion via investments through foreign tax havens and other avenues. Any assertion that the Subsidiary is in violation of GAAR or any change in the requirements established by Mauritius to qualify as a Mauritius resident could result in the imposition by India of various taxes on Indian securities invested in by the Subsidiary (and indirectly by the Fund). Further, the governments of India and Mauritius signed a protocol amending the India-Mauritius tax treaty, which will result in the imposition of Indian tax on gains resulting from the alienation of shares in an Indian company if the shares were acquired by the Subsidiary on or after April 1, 2017. Such gains on shares acquired from April 1, 2017 through March 31, 2019 will be taxed at 50% of the applicable Indian tax rate under certain circumstances, for which neither the Fund nor the Subsidiary qualify. The imposition of taxes on the Subsidiary by India for any of the reasons described herein would result in higher taxes and lower returns for the Fund and its shareholders.

Mid-Cap Company Securities Risk. Investments in mid-capitalization companies (mid-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because mid-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies, and may be less liquid than the securities of larger companies.

New Fund Risk. The Fund is a newly-formed ETF. Accordingly, investors in the Fund bear the risk that the Fund may not be successful in implementing its investment strategy of replicating the Index, which could result in the Fund being liquidated at any time without shareholder approval and/or at a time that may not be favorable for shareholders. Such a liquidation could have negative tax consequences for shareholders.

Portfolio Turnover Risk. In seeking to meet its investment objective, the Fund may incur portfolio turnover to manage the Fund’s investment exposure. Additionally, active market trading of the Fund’s shares may cause more frequent creation or redemption activities that could, in certain circumstances, increase the number of portfolio transactions as well as tracking error to the Index. High levels of transactions increase brokerage and other transaction costs and may result in increased taxable capital gains.

Secondary Market Trading Risk. Investors buying or selling Fund shares will pay brokerage commissions or other charges imposed by brokers as determined by that broker. Brokerage commissions are often a fixed amount and may be a significant proportional cost for investors seeking to buy or sell relatively small amounts of Fund shares.

Sector Risk. At times, the Fund may have a significant portion of its assets invested in securities of companies conducting business in a related group of industries within a sector. Companies in the same sector may be similarly affected by economic, regulatory, political or market events or conditions, which may make the Fund more vulnerable to unfavorable developments in that sector than funds that invest more broadly. Generally, the more broadly the Fund invests, the more it spreads risk and potentially reduces the risks of loss and volatility.

Consumer Discretionary/Staples Sectors. The Fund may be more susceptible to the particular risks that may affect companies in the consumer discretionary/staples sectors than if it were invested in a wider variety of companies in unrelated sectors. Companies in the consumer discretionary/staples sectors are subject to certain risks, including fluctuations in the performance of the overall domestic and international economy, interest rate changes, currency exchange rates, increased competition and consumer confidence. Performance of such companies may be affected by factors including reduced disposable household income, reduced consumer spending, changing demographics and consumer tastes.

Financial Services Sector. The Fund may be more susceptible to the particular risks that may affect companies in the financial services sector than if it were invested in a wider variety of companies in unrelated sectors. Companies in the financial services sector are subject to certain risks, including the risk of regulatory change, decreased liquidity in credit markets and unstable interest rates. Such companies may have concentrated portfolios, such as a high level of loans to real estate developers, which makes them vulnerable to economic conditions that affect that industry. Performance of such companies may be affected by competitive pressures and exposure to investments or agreements that, under certain circumstances, may lead to losses (e.g., subprime loans). Companies in the financial services sector are subject to extensive governmental regulation that may limit the amount and types of loans and other financial commitments they can make, and interest rates and fees that they may charge. In addition, profitability of such companies is largely dependent upon the availability and the cost of capital.

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Information Technology and Technology-Related Sectors. The Fund may be more susceptible to the particular risks that may affect companies in the information technology sector, as well as other technology-related sectors (collectively, the technology sectors) than if it were invested in a wider variety of companies in unrelated sectors. Companies in the technology sectors are subject to certain risks, including the risk that new services, equipment or technologies will not be accepted by consumers and businesses or will become rapidly obsolete. Performance of such companies may be affected by factors including obtaining and protecting patents (or the failure to do so) and significant competitive pressures, including aggressive pricing of their products or services, new market entrants, competition for market share and short product cycles due to an accelerated rate of technological developments. Such competitive pressures may lead to limited earnings and/or falling profit margins. As a result, the value of their securities may fall or fail to rise. In addition, many technology sector companies have limited operating histories and prices of these companies’ securities historically have been more volatile than other securities, especially over the short term.

Small Company Securities Risk. Investments in small-capitalization companies (small-cap companies) often involve greater risks than investments in larger, more established companies (larger companies) because small-cap companies tend to have less predictable earnings and may lack the management experience, financial resources, product diversification and competitive strengths of larger companies, and securities of small-cap companies may be less liquid and more volatile than the securities of larger companies.

Treaty/Tax Risk — The India-Mauritius Tax Treaty. The Fund and the Subsidiary have historically relied on a tax treaty between India and Mauritius for relief from certain Indian taxes. India and Mauritius have agreed to an amended protocol with respect to gains resulting from the alienation of shares in Indian companies acquired on or after April 1, 2017, which will result in higher taxes paid indirectly by the Fund and, therefore, lower returns for the Fund and its shareholders. Gains resulting from the alienation of shares acquired prior to April 1, 2017 will continue to be exempt from Indian tax under the India-Mauritius tax treaty. Additionally, India has enacted general anti-avoidance rules, the application of which could result in the imposition by India of various additional taxes on Indian securities invested in by the Subsidiary (and indirectly the Fund).

The rest of the section remains the same.

Shareholders should retain this Supplement for future reference.

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