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Fees and Expenses This table describes the fees and expenses that you may pay when you buy, hold, and sell shares of the fund. Investors may also pay commissions or other fees to their financial intermediaries when they buy, hold, and sell shares of the fund, which are not reflected below. Shareholder Fees (fees paid directly from your investment): 0 0 Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment): 0.0025 0.0000 0.0025 Example This example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not take into account brokerage commissions or other fees that you may pay to your financial intermediary when purchasing or selling shares of the fund.The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods; your investment has a 5% return each year; and the fund’s operating expenses remain the same. Although your actual costs will likely be higher or lower, under these assumptions your costs would be: 26 80 Portfolio Turnover The fund pays 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 shares are held in a taxable account. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance. The portfolio turnover rate for the fund is not available because the fund had not commenced operations as of the date of this prospectus. Principal Investment Strategies MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests the fund’s assets primarily in debt instruments. Debt instruments include U.S. Government securities, corporate debt instruments, foreign government securities, securitized instruments (including mortgage-backed securities and other asset-backed securities), and other obligations to repay money borrowed. In managing the fund, MFS employs a short duration investment strategy whereby the dollar-weighted average effective duration of the fund’s portfolio will approximate that of the Bloomberg 1-5 Year Government/Credit Bond Index plus or minus 1 year. Duration is a measure of a debt instrument’s or a portfolio of debt instruments’ sensitivity to a change in interest rates expressed in years. For example, if a debt instrument has a 3-year duration and interest rates rise 1%, the debt instrument’s value is likely to fall approximately 3%.MFS primarily invests the fund’s assets in investment grade quality debt instruments, but may also invest the fund’s assets in below investment grade quality debt instruments. MFS invests the fund’s assets in U.S. securities and U.S. dollar-denominated foreign securities, which may include emerging market securities.MFS normally invests the fund's assets across different industries, sectors, countries, and regions, but MFS may invest a significant percentage of the fund’s assets in issuers in a single industry, sector, country, or region. MFS may invest a significant percentage of the fund’s assets in a single issuer or a small number of issuers.While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, and swaps.MFS uses an active bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual instruments and their issuers. Quantitative screening tools that systematically evaluate instruments may also be considered. In structuring the fund, MFS also considers top-down factors. Principal Risks As with any exchange-traded fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. 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 governmental agency.The principal risks of investing in the fund are: As with any exchange-traded fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. 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 governmental agency. Investment Selection Risk: MFS' investment analysis and its selection of investments may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests. In addition, to the extent MFS considers quantitative tools in managing the fund, such tools may not produce the intended results. Debt Market Risk: Debt markets can be volatile and can decline significantly in response to changes in, or investor perceptions of, issuer, market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. These conditions can affect a single instrument, issuer, or borrower, a particular type of instrument, issuer, or borrower, a segment of the debt markets or the debt markets generally. Certain events can have a dramatic adverse effect on debt markets and may lead to periods of high volatility and reduced liquidity in a debt market or segment of a debt market. Interest Rate Risk: In general, the price of a debt instrument falls when interest rates rise and rises when interest rates fall. Interest rate risk is generally greater for instruments with longer maturities or durations, or that do not pay current interest. Credit Risk: The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or other entity responsible for payment, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in, or perceptions of, the financial condition of the issuer, borrower, counterparty, or other entity, or underlying collateral or assets, or changes in, or perceptions of, specific or general market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. Debt instruments may be more susceptible to downgrades or defaults during economic downturns or similar periods of economic stress, which in turn could negatively affect the market value and liquidity of a debt instrument.Below investment grade quality debt instruments (commonly referred to as “high yield securities” or “junk bonds”) can involve a substantially greater risk of default or can already be in default, and their values can decline significantly. Below investment grade quality debt instruments are regarded as having predominantly speculative characteristics. Below investment grade quality debt instruments tend to be more sensitive to adverse news about the issuer, or the market or economy in general, than higher quality debt instruments. Foreign Risk: Exposure to foreign markets through issuers can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. These factors can make foreign investments, especially those tied economically to countries with developing economies or countries subject to sanctions or the threat of new or modified sanctions, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market. Focus Risk: Issuers in a single industry, sector, country, or region can react similarly to market, currency, political, economic, regulatory, geopolitical, environmental, public health, and other conditions, and the fund's performance will be affected by the conditions in the industries, sectors, countries, and regions to which the fund is exposed. Furthermore, investments in particular industries, sectors, countries, or regions may be more volatile than the broader market as a whole. If MFS invests a significant percentage of the fund's assets in a single issuer or small number of issuers, the fund’s performance could be more volatile than the performance of more diversified funds. Prepayment/Extension Risk: Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument’s holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended. Derivatives Risk: Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s) on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives’ original cost. Derivatives can involve leverage. Leveraging Risk: Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses. Counterparty and Third Party Risk: Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty’s or third party’s ability or willingness to perform in accordance with the terms of the transaction. Liquidity Risk: It may be difficult to value, and it may not be possible to sell, certain investments, types of investments, and/or investments in certain segments of the market, and the fund may have to sell certain of these investments at prices or times that are not advantageous in order to meet redemptions or other cash needs. Fluctuation of Net Asset Value and Share Price Risk: The net asset value (NAV) per share of the fund will generally fluctuate with changes in the market value of the fund’s holdings. The fund’s shares can be bought and sold in the secondary market at market prices. Disruptions to purchases and sales, the existence of extreme market volatility, and/or a lack of an active trading market for the fund's shares may result in the fund's shares trading significantly above (at a premium) or below (at a discount) to NAV and bid/ask spreads may widen. Shares of the fund may trade at a larger premium or discount to the NAV than shares of other ETFs that focus on other market segments or types of securities. In addition, in stressed market conditions or periods of market disruption or volatility, the market for shares of the fund may become less liquid in response to deteriorating liquidity in the markets for the fund’s underlying portfolio holdings. If you buy fund shares when their market price is at a premium or sell fund shares when their market prices is at a discount, you may pay more than, or receive less than, NAV, respectively. Authorized Participant Risks: Only financial institutions authorized to transact daily with the fund (Authorized Participants) may engage in creation or redemption transactions directly with the fund, and Authorized Participants are not obligated to do so. To the extent an Authorized Participant cannot or is otherwise unwilling to engage in creation and redemption transactions, and no other Authorized Participant engages in such transactions, shares of the fund may trade at a significant discount or premium to NAV, experience wider intraday bid/ask spreads, and may face trading halts and/or delisting from the exchange. Trading Issues Risk: There can be no assurance that an active trading market for the fund’s shares will develop or be maintained. In addition, trading of the fund’s shares may be halted or become less liquid. Shares of the fund, similar to shares of other issuers listed on a stock exchange, may be sold short and are therefore subject to the risk of increased volatility and price decreases associated with being sold short.Most fund investors will buy and sell fund shares on the listing exchange or on another secondary market. When buying or selling shares of the fund, investors typically will pay brokerage commissions or other charges imposed by financial intermediaries as determined by that financial intermediary. Cash Transactions Risk: Unlike certain ETFs that distribute portfolio securities entirely in-kind, the fund may effect some or all creations and redemptions using cash, rather than in-kind securities. As a result, an investment in the fund may be less tax-efficient than an investment in an ETF that distributes portfolio securities entirely in-kind. Performance Information The bar chart and performance table are not included because the fund has not had a full calendar year of operations. Once the fund has commenced operations, updated performance information will be available online at mfs.com. Past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. mfs.com MFS® Active Short Muni Bond ETF Summary of Key Information MFSX Investment Objective The fund’s investment objective is to seek total return with an emphasis on income exempt from U.S. federal income tax, but also considering capital preservation. Fees and Expenses This table describes the fees and expenses that you may pay when you buy, hold, and sell shares of the fund. Investors may also pay commissions or other fees to their financial intermediaries when they buy, hold, and sell shares of the fund, which are not reflected below. Shareholder Fees (fees paid directly from your investment): 0 0 Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment): 0.0025 0.0000 0.0025 Example This example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. The example does not take into account brokerage commissions or other fees that you may pay to your financial intermediary when purchasing or selling shares of the fund.The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods; your investment has a 5% return each year; and the fund’s operating expenses remain the same. Although your actual costs will likely be higher or lower, under these assumptions your costs would be: 26 80 Portfolio Turnover The fund pays 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 shares are held in a taxable account. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance. The portfolio turnover rate for the fund is not available because the fund had not commenced operations as of the date of this prospectus. Principal Investment Strategies MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests the fund’s assets primarily in municipal instruments. MFS defines municipal instruments as debt instruments issued by or for states, territories, or possessions of the United States or by their political subdivisions, agencies, authorities, or other government entities, to raise money for a variety of public and private purposes, including general financing for state and local governments, or financing for a specific project or public facility. Municipal instruments include general obligation bonds of municipalities, state or local governments, project or revenue-specific bonds, municipal lease obligations, and pre-refunded or escrowed bonds. MFS normally invests at least 80% of the fund’s net assets in municipal instruments, the interest on which is exempt from U.S. federal income tax. However, interest from the fund’s investments may be subject to the U.S. federal alternative minimum tax.In managing the fund, MFS employs a short duration investment strategy whereby the dollar-weighted average effective duration of the fund’s portfolio will not normally exceed three years. Duration is a measure of a debt instrument’s or a portfolio of debt instruments’ sensitivity to a change in interest rates expressed in years. For example, if a debt instrument has a 3-year duration and interest rates rise 1%, the debt instrument’s value is likely to fall approximately 3%.MFS primarily invests the fund’s assets in investment grade quality debt instruments, but may also invest the fund’s assets in below investment grade quality debt instruments. MFS may invest 25% or more of the fund’s total assets in municipal instruments that finance similar types of projects, such as those relating to education, healthcare, housing, utilities, water, or sewers. MFS may invest a significant percentage of the fund's assets in issuers in a single state, territory, or possession, or a small number of states, territories, or possessions.While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, inverse floating rate instruments, and swaps.MFS uses an active bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual instruments and their issuers. Quantitative screening tools that systematically evaluate instruments may also be considered. In structuring the fund, MFS also considers top-down factors.For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes. MFS defines municipal instruments as debt instruments issued by or for states, territories, or possessions of the United States or by their political subdivisions, agencies, authorities, or other government entities, to raise money for a variety of public and private purposes, including general financing for state and local governments, or financing for a specific project or public facility. Municipal instruments include general obligation bonds of municipalities, state or local governments, project or revenue-specific bonds, municipal lease obligations, and pre-refunded or escrowed bonds. MFS normally invests at least 80% of the fund’s net assets in municipal instruments, the interest on which is exempt from U.S. federal income tax. Principal Risks As with any exchange-traded fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. 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 governmental agency.The principal risks of investing in the fund are: As with any exchange-traded fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. 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 governmental agency. Investment Selection Risk: MFS' investment analysis and its selection of investments may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests. In addition, to the extent MFS considers quantitative tools in managing the fund, such tools may not produce the intended results. Debt Market Risk: Debt markets can be volatile and can decline significantly in response to changes in, or investor perceptions of, issuer, market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. These conditions can affect a single instrument, issuer, or borrower, a particular type of instrument, issuer, or borrower, a segment of the debt markets or the debt markets generally. Certain events can have a dramatic adverse effect on debt markets and may lead to periods of high volatility and reduced liquidity in a debt market or segment of a debt market. Interest Rate Risk: In general, the price of a debt instrument falls when interest rates rise and rises when interest rates fall. Interest rate risk is generally greater for instruments with longer maturities or durations, or that do not pay current interest. Credit Risk: The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or other entity responsible for payment, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in, or perceptions of, the financial condition of the issuer, borrower, counterparty, or other entity, or underlying collateral or assets, or changes in, or perceptions of, specific or general market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. Debt instruments may be more susceptible to downgrades or defaults during economic downturns or similar periods of economic stress, which in turn could negatively affect the market value and liquidity of a debt instrument.The credit quality of, and the ability to pay principal and interest when due by, an issuer of a municipal instrument depends on the credit quality of the entity supporting the municipal instrument, how essential any services supported by the municipal instrument are, the sufficiency of any revenues or taxes that support the municipal instrument, and/or the willingness or ability of the appropriate government entity to approve any appropriations necessary to support the municipal instrument. In addition, the price of a municipal instrument also depends on its credit quality and ability to meet the credit support obligations of any insurer or other entity providing credit support to a municipal instrument. Below investment grade quality debt instruments (commonly referred to as “high yield securities” or “junk bonds”) can involve a substantially greater risk of default or can already be in default, and their values can decline significantly. Below investment grade quality debt instruments are regarded as having predominantly speculative characteristics. Below investment grade quality debt instruments tend to be more sensitive to adverse news about the issuer, or the market or economy in general, than higher quality debt instruments. Municipal Risk: The price of a municipal instrument can be volatile and significantly affected by adverse tax changes or court rulings, legislative or political changes, changes in specific or general market and economic conditions and developments, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in certain industries can significantly affect the fund and the overall municipal market. Municipal instruments may be more susceptible to downgrades or defaults during economic downturns or similar periods of economic stress, which in turn could affect the market values and marketability of many or all municipal obligations of issuers in a state, U.S. territory, or possession. In addition, because some municipal obligations may be secured or guaranteed by banks and other institutions, the risk associated with investments in such municipal securities could increase if the banking or financial sector suffers an economic downturn and/or if the credit ratings of the institutions issuing the guarantee are downgraded or at risk of being downgraded by a national rating organization. If such events occur, the value of the security could decrease or the value could be lost entirely, and it may be difficult or impossible to sell the security at the time and the price that normally prevails in the market. Focus Risk: The fund’s performance will be closely tied to the issuer, market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions in the states, territories, and possessions of the United States in which the fund's assets are invested. If MFS invests a significant percentage of the fund's assets in a single state, territory, or possession, or a small number of states, territories, or possessions, these conditions will have a significant impact on the fund's performance and the fund's performance may be more volatile than the performance of more geographically-diversified funds. Prepayment/Extension Risk: Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument’s holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended. Derivatives Risk: Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s) on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives’ original cost. Derivatives can involve leverage. Leveraging Risk: Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses. Counterparty and Third Party Risk: Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty’s or third party’s ability or willingness to perform in accordance with the terms of the transaction. Liquidity Risk: It may be difficult to value, and it may not be possible to sell, certain investments, types of investments, and/or investments in certain segments of the market, and the fund may have to sell certain of these investments at prices or times that are not advantageous in order to meet redemptions or other cash needs. Fluctuation of Net Asset Value and Share Price Risk: The net asset value (NAV) per share of the fund will generally fluctuate with changes in the market value of the fund’s holdings. The fund’s shares can be bought and sold in the secondary market at market prices. Disruptions to purchases and sales, the existence of extreme market volatility, and/or a lack of an active trading market for the fund's shares may result in the fund's shares trading significantly above (at a premium) or below (at a discount) to NAV and bid/ask spreads may widen. Shares of the fund may trade at a larger premium or discount to the NAV than shares of other ETFs that focus on other market segments or types of securities. In addition, in stressed market conditions or periods of market disruption or volatility, the market for shares of the fund may become less liquid in response to deteriorating liquidity in the markets for the fund’s underlying portfolio holdings. If you buy fund shares when their market price is at a premium or sell fund shares when their market prices is at a discount, you may pay more than, or receive less than, NAV, respectively. Authorized Participant Risks: Only financial institutions authorized to transact daily with the fund (Authorized Participants) may engage in creation or redemption transactions directly with the fund, and Authorized Participants are not obligated to do so. To the extent an Authorized Participant cannot or is otherwise unwilling to engage in creation and redemption transactions, and no other Authorized Participant engages in such transactions, shares of the fund may trade at a significant discount or premium to NAV, experience wider intraday bid/ask spreads, and may face trading halts and/or delisting from the exchange. Trading Issues Risk: There can be no assurance that an active trading market for the fund’s shares will develop or be maintained. In addition, trading of the fund’s shares may be halted or become less liquid. Shares of the fund, similar to shares of other issuers listed on a stock exchange, may be sold short and are therefore subject to the risk of increased volatility and price decreases associated with being sold short.Most fund investors will buy and sell fund shares on the listing exchange or on another secondary market. When buying or selling shares of the fund, investors typically will pay brokerage commissions or other charges imposed by financial intermediaries as determined by that financial intermediary. Cash Transactions Risk: Unlike certain ETFs that distribute portfolio securities entirely in-kind, the fund may effect some or all creations and redemptions using cash, rather than in-kind securities. As a result, an investment in the fund may be less tax-efficient than an investment in an ETF that distributes portfolio securities entirely in-kind. Performance Information The bar chart and performance table are not included because the fund has not had a full calendar year of operations. Once the fund has commenced operations, updated performance information will be available online at mfs.com. 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