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2025-12-31 0000867969 cik0000867969:S000002537Member cik0000867969:MSCIEAFEEuropeAustralasiaFarEastIndexnetdiv31Member 2016-01-01 2025-12-31 iso4217:USD pure N-1A MFS® SERIES TRUST XVII 2026-10-28 2026-10-28 MFS® International Equity Fund Summary of Key Information MIEJX MIEKX MIEIX Investment Objective The fund’s investment objective is to seek capital appreciation. 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. You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS funds. More information about these and other waivers and reductions is available from your financial intermediary and in “Sales Charges and Waivers and Reductions” on page 10 and “Appendix A – Waivers and Reductions of Sales Charges” on page A-1 of the fund’s prospectus. You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS funds. 50000 Shareholder Fees (fees paid directly from your investment): 0.0575 0 0 0.0100 0 0 Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment): 0.0060 0.0060 0.0060 0.0025 0 0 0.0011 0.0011 0.0002 0.0096 0.0071 0.0062 -0.0001 -0.0001 -0.0001 0.0095 0.0070 0.0061 Example This 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 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: 666 862 1074 1684 72 226 394 882 62 198 345 773 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. During the most recent fiscal year, the fund’s portfolio turnover rate was 25% of the average value of its portfolio. 0.25 Principal Investment Strategies MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests at least 80% of the fund’s net assets in equity securities. Equity securities include common stocks, depositary receipts, and other securities that represent an ownership interest (or right to acquire an ownership interest) in a company or other issuer.MFS normally invests the fund’s assets primarily in foreign securities, including emerging market securities. Emerging market countries are countries with financial and capital markets in the development phase. Emerging market countries include countries located in Latin America, Asia, Africa, the Middle East, and developing countries of Europe, primarily Eastern Europe. In selecting investments for the fund, MFS is not constrained by any particular investment style. MFS may invest the fund’s assets in the stocks of companies it believes to have above average earnings growth potential compared to other companies (growth companies), in the stocks of companies it believes are undervalued compared to their perceived worth (value companies), or in a combination of growth and value companies. MFS may invest the fund’s assets in securities of companies of any size. 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 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 issuers. Quantitative screening tools that systematically evaluate issuers may also be considered.For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes. MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests at least 80% of the fund’s net assets in equity securities. Equity securities include common stocks, depositary receipts, and other securities that represent an ownership interest (or right to acquire an ownership interest) in a company or other issuer. Principal Risks As with any mutual 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 mutual 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. Equity Market Risk/Company Risk: Equity markets are 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 issuer or type of security, issuers within a broad market sector, industry or geographic region, or the equity markets in general. Certain events can have a dramatic adverse effect on equity markets and may lead to periods of high volatility in an equity market or a segment of an equity market. The value of an investment held by the fund may decline due to factors directly related to the issuer. Growth Company Risk: The stocks of growth companies can be more sensitive to the company’s earnings and more volatile than the market in general. Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general. Foreign Risk: Exposure to foreign markets through issuers or currencies 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 emerging markets 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. Emerging Markets Risk: Investments tied economically to emerging markets, especially frontier markets, can involve additional and greater risks than the risks associated with investments in developed markets. Emerging markets can have less developed markets, greater custody and operational risk, less developed legal, regulatory, and accounting systems, greater government involvement in the economy, greater risk of new or inconsistent government treatment of or restrictions on issuers and instruments, and greater political, social, geopolitical, and economic instability than developed markets. Currency Risk: The value of foreign currencies relative to the U.S. dollar fluctuates in response to market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions, and changes in currency exchange rates impact the financial condition of companies or other issuers and may change the value in U.S. dollars of investments denominated in foreign currencies. 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. 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. Large Shareholder Risk: From time to time, shareholders of the fund (which may include institutional investors, financial intermediaries, or other MFS funds) may make relatively large redemptions or purchases of fund shares. These transactions may cause the fund to sell securities or invest additional cash, as the case may be, at disadvantageous prices. Redemptions of a large number of shares also may increase transaction and other costs or have adverse tax consequences for shareholders of the fund by requiring a sale of portfolio securities. Purchases of a large number of shares may adversely affect the fund's performance to the extent that it takes time to invest new cash and the fund maintains a larger cash position than it ordinarily would. Performance Information The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of a broad measure of market performance.Performance information shown in the “Class R6 Bar Chart” and the performance for Class R6 shares in the “Performance Table” reflects any applicable fee reductions and waivers and expense reimbursements in effect during the periods shown; without these, the performance would have been lower. The fund commenced operations on January 31, 1996. Prior to October 24, 2022, the fund’s shares did not have a share class designation. Effective October 24, 2022, the fund’s existing undesignated shares were designated Class R6 shares. The fund subsequently offered Class A and Class I shares on February 8, 2023.In the “Performance Table,” performance for Class A and Class I shares for periods prior to their offering is derived from the historical performance of the fund’s Class R6 shares, adjusted to take into account differences in sales loads and class specific operating expenses, such as Rule 12b-1 fees and certain shareholder servicing (including sub-accounting) costs, if any. In addition, the performance shown for Class A and Class I shares for periods prior to their offering does not reflect any applicable fee reductions and waivers and expense reimbursements that were in effect prior to the offering of Class A and Class I shares.The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606. The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of a broad measure of market performance. The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. mfs.com 1-800-225-2606 Class R6 Bar Chart. The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown. The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown. The total return for the nine-month period ended September 30, 2026, was 5.08%. During the period(s) shown in the bar chart, the highest quarterly return was 16.19% (for the calendar quarter ended December 31, 2022) and the lowest quarterly return was (19.89)% (for the calendar quarter ended March 31, 2020). The total return for the nine-month period ended 2026-09-30 0.0508 highest quarterly return 0.1619 2022-12-31 lowest quarterly return -0.1989 2020-03-31 Performance Table. Average Annual Total Returns (For the Periods Ended December 31, 2025) Returns Before Taxes Returns Before Taxes Returns Before Taxes 0.1576 0.0682 0.0843 0.2313 0.0836 0.0935 0.2323 0.0843 0.0939 Returns After Taxes on Distributions 0.2258 0.0797 0.0899 Returns After Taxes on Distributions and Sale of Fund Shares 0.1442 0.0673 0.0776 Reflects no deduction for fees, expenses, or taxes MSCI EAFE (Europe, Australasia, Far East) Index (net div) 0.3122 0.0892 0.0818 After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown. 485BPOS 2026-10-28 2026-06-30 0000867969 2026-10-27 false ~ http://xbrl.sec.gov/rr/role/ShareholderFeesData row dei_DocumentInformationDocumentAxis compact cik0000867969_S000002537Summary1Member row dei_LegalEntityAxis compact cik0000867969_S000002537Member ~ ~ http://xbrl.sec.gov/rr/role/OperatingExpensesData row dei_DocumentInformationDocumentAxis compact cik0000867969_S000002537Summary1Member row dei_LegalEntityAxis compact cik0000867969_S000002537Member ~ ~ http://xbrl.sec.gov/rr/role/ExpenseExample row dei_DocumentInformationDocumentAxis compact cik0000867969_S000002537Summary1Member row dei_LegalEntityAxis compact cik0000867969_S000002537Member ~ ~ http://xbrl.sec.gov/rr/role/PerformanceTableData column period compact * row dei_DocumentInformationDocumentAxis compact cik0000867969_S000002537Summary1Member row dei_LegalEntityAxis compact cik0000867969_S000002537Member row oef_ClassAxis compact * row oef_PerformanceMeasureAxis compact * ~ 0.003 0.2802 -0.1066 0.284 0.111 0.1516 -0.1483 0.1904 0.0414 0.2323 This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase. October 31, 2027 October 31, 2027 October 31, 2027 ~ http://www.MFS.com/20260630/role/RRRiskTable3 ~ This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase. Massachusetts Financial Services Company (MFS) has agreed in writing to waive at least 0.01% of the fund's management fee as part of an agreement pursuant to which MFS has agreed to reduce its management fee by a specified amount if certain MFS mutual fund assets exceed thresholds agreed to by MFS and the fund's Board of Trustees. The agreement to waive at least 0.01% of the management fee will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least October 31, 2027.