# EDGAR Filing Document

**Accession Number:** 0000783740
**File Stem:** 0000912938-26-000563
**Filing Date:** 2026-5
**Character Count:** 23406
**Document Hash:** 9a3d8ee144077b8999e5dda21454bbdd
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0000912938-26-000563.hdr.sgml**: 20260512

**ACCESSION NUMBER**: 0000912938-26-000563

**CONFORMED SUBMISSION TYPE**: 497

**PUBLIC DOCUMENT COUNT**: 16

**FILED AS OF DATE**: 20260512

**DATE AS OF CHANGE**: 20260512

**EFFECTIVENESS DATE**: 20260512

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** MFS SERIES TRUST X
- **CENTRAL INDEX KEY:** 0000783740

**ORGANIZATION NAME:**
- **EIN:** 000000000
- **STATE OF INCORPORATION:** MA
- **FISCAL YEAR END:** 1130

**FILING VALUES:**
- **FORM TYPE:** 497
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 033-01657
- **FILM NUMBER:** 26966913

**BUSINESS ADDRESS:**
- **STREET 1:** 111 HUNTINGTON AVENUE
- **STREET 2:** 21ST FLOOR
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02199
- **BUSINESS PHONE:** 18006372929

**MAIL ADDRESS:**
- **STREET 1:** 111 HUNTINGTON AVENUE
- **STREET 2:** 21ST FLOOR
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02199

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** MFS GOVERNMENT MORTGAGE FUND
- **DATE OF NAME CHANGE:** 19930408

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** MFS GOVERNMENT INCOME PLUS FUND
- **DATE OF NAME CHANGE:** 19930312

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** MASSACHUSETTS MFS GOVERNMENT INCOME PLUS FUND
- **DATE OF NAME CHANGE:** 19921015

## Series and Classes Contracts Data

### MFS International Diversification Fund (Series ID: S000002515)

---

|  |  |  |
|:---|:---|:---|
| Class Name | Ticker Symbol | Class ID   |
| A          | MDIDX         | C000006924 |
| R4         | MDITX         | C000006925 |
| B          | MDIFX         | C000006929 |
| C          | MDIGX         | C000006930 |
| I          | MDIJX         | C000006931 |
| R1         | MDIOX         | C000006933 |
| R2         | MDIKX         | C000006935 |
| R3         | MDIHX         | C000006936 |
| R6         | MDIZX         | C000195683 |

---

## Series and Classes Contracts Data

### MFS International Diversification Fund (Series ID: S000002515)

| Class ID   | Class Name   | Ticker Symbol   |
|:---|:---|:---|
| C000006924 | A            | MDIDX           |
| C000006925 | R4           | MDITX           |
| C000006929 | B            | MDIFX           |
| C000006930 | C            | MDIGX           |
| C000006931 | I            | MDIJX           |
| C000006933 | R1           | MDIOX           |
| C000006935 | R2           | MDIKX           |
| C000006936 | R3           | MDIHX           |
| C000195683 | R6           | MDIZX           |

?xml version='1.0' encoding='ASCII'?

![](img_8fe646ad56b14f1.jpg)

SUPPLEMENT TO THE PROSPECTUS

*Supplement dated May 12, 2026, to the Prospectus dated September 26, 2025.*

## MFS <sup>®</sup> International Diversification Fund
**Effective immediately, the second paragraph and table in the sub-sections entitled "Principal Investment Strategies" under the main heading entitled "Summary of Key Information" and under the main heading entitled "Investment Objective, Strategies, and Risks" are restated in their entirety as follows:**

As of September 1, 2025, the fund's target allocation among underlying funds was:

---

| | |
|:---|:---|
| MFS Emerging Markets Equity Fund | 17.5% |
| MFS International Growth Fund | 15% |
| MFS International Intrinsic Equity Fund<sup>1</sup> | 15% |
| MFS International Large Cap Value Fund<sup>2</sup> | 15% |
| MFS International New Discovery Fund | 10% |
| MFS Research International Fund | 27.5% |

---

<sup>1</sup> Effective April 30, 2026, the name of MFS International Intrinsic Value Fund changed to MFS

International Intrinsic Equity Fund.

<sup>2</sup> Effective August 1, 2026, the name of MFS International Large Cap Value Fund will change to

MFS International Value Fund.

**-- End of Supplement Data --**

#### Effective immediately, the section under the main heading entitled "Appendix B - Description of Underlying Funds" is restated in its entirety as follows:

#### Appendix B - Description of Underlying Funds
Further information about each underlying fund, including a copy of an underlying fund's most recent prospectus, SAI, Annual and Semi-Annual Reports, financial statements, and other information, may be obtained on the fund's Website at **mfs.com**, or by contacting MFSC.

#### MFS Emerging Markets Equity Fund

#### Investment Objective
The fund's investment objective is to seek capital appreciation. The fund's objective may be changed without shareholder approval.

#### Principal Investment Strategies
MFS normally invests at least 80% of the fund's net assets in equity securities of issuers that are tied economically to emerging market countries. Emerging markets are countries determined to have emerging market economies based on factors that demonstrate the country's financial and capital markets are in the development

phase, including whether a particular country has a low- to middle-income economy according to the International Bank for Reconstruction and Development (the World Bank), the country's designation by the International Monetary Fund as an emerging market, or the country's inclusion in an emerging market index. Emerging market countries include countries located in Latin America, Asia, Africa, the Middle East, and developing countries of Europe, primarily Eastern Europe. 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 generally considers the issuer of a security or other investment to be tied economically to emerging market countries if: (i) the security or other investment is issued or guaranteed by the government of an emerging market country or any of its agencies, authorities or instrumentalities; (ii) the issuer is organized under the laws of, and maintains a principal office in, an emerging market country; (iii) the issuer has its principal securities trading market in an emerging market country; (iv) a third party has identified an emerging market country as the issuer's "country of risk"; (v) the issuer is included in an index which is representative of emerging market countries; (vi) the issuer derives 50% or more of its total revenues from goods sold or services performed in emerging market countries; or (vii) the issuer has 50% or more of its assets in emerging market countries.

MFS may also invest the fund's assets in equity securities of issuers that are not tied economically to emerging market countries.

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 may invest a significant percentage of the fund's assets in a single issuer or a small number of issuers.

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 and their potential in light of their financial condition, and market, economic, political, and regulatory conditions. Factors considered may include analysis of an issuer's earnings, cash flows, competitive position, and management ability. MFS may also consider environmental, social, and governance (ESG) factors in its fundamental investment analysis where MFS believes such factors could materially impact the economic value of an issuer. ESG factors considered may include, but are not limited to, climate change, resource depletion, an issuer's governance structure and practices, data protection and privacy issues, and diversity and labor practices. Quantitative screening tools that systematically evaluate an issuer's valuation, price and earnings momentum, earnings quality, and other factors, may also be considered.

MDI-SUP-I-051226

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MFS International Diversification Fund

For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes.

#### MFS International Growth Fund

#### Investment Objective
The fund's investment objective is to seek capital appreciation. The fund's objective may be changed without shareholder approval.

#### Principal Investment Strategies

#### Effective June 10, 2026, the following paragraph is added:
MFS normally invests at least 80% of the fund's net assets in growth companies. Growth companies are companies that MFS believes have above average earnings growth potential compared to other companies. MFS considers a number of factors when determining a company's growth potential, including whether (i) the issuer is included in an index that is representative of growth companies; (ii) the issuer is classified as a growth company by an independent third party financial data provider; and/or (iii) the issuer exhibits the characteristics of a growth company, considering metrics such as historical and/or projected growth rates relative to the applicable equity market. Growth companies tend to have stock prices that are high relative to their earnings, dividends, book value, or other financial measures.

MFS normally invests the fund's assets primarily in foreign equity securities, including emerging market equity securities.

#### Effective June 10, 2026, the following paragraph is deleted in its entirety:
MFS focuses on investing the fund's assets in the stocks of companies it believes to have above average earnings growth potential compared to other companies (growth companies). Growth companies tend to have stock prices that are high relative to their earnings, dividends, book value, or other financial measures.

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 and their potential in light of their financial condition, and market, economic, political, and regulatory conditions. Factors considered may include analysis of an issuer's earnings, cash flows, competitive position, and management ability. MFS may also consider environmental, social, and governance (ESG) factors in its fundamental investment analysis where MFS believes such factors could materially impact the economic value of an issuer. ESG factors considered may include, but are not limited to, climate change, resource depletion, an issuer's governance structure and practices, data protection and privacy issues, and diversity and labor practices. Quantitative screening tools that systematically evaluate an issuer's valuation, price and earnings momentum, earnings quality, and other factors, may also be considered.

#### Effective June 10, 2026, the following sentence is added as its own paragraph:
For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes.

#### MFS International Intrinsic Equity Fund
*(Formerly MFS International Intrinsic Value Fund)*

#### Investment Objective
The fund's investment objective is to seek capital appreciation. The fund's objective may be changed without shareholder approval.

#### Principal Investment Strategies
MFS 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 equity securities, including emerging market equity securities.

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. In managing the fund, MFS assesses the intrinsic valuation of issuers by considering the full context of how a company's cash flows are generated. MFS focuses on companies it believes have conservative balance sheets, sustainable competitive advantages, high returns on capital, and/or the ability to weather economic downturns, among other factors. Many of the factors considered by MFS in assessing issuers are qualitative in nature and require subjective judgment and interpretation.

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.

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 currency exposure.

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 and their potential in light of their financial condition, and market, economic, political, and regulatory conditions. Factors considered may include analysis of an issuer's earnings, cash flows, competitive position, and management ability. MFS may also consider environmental, social, and governance (ESG) factors in its fundamental investment analysis where MFS believes such factors could materially impact the economic value of an issuer. ESG factors considered may include, but are not limited to, climate change, resource depletion, an issuer's governance structure and practices, data protection and privacy issues, and diversity and labor practices. Quantitative screening tools that systematically evaluate an issuer's valuation, price and earnings momentum, earnings quality, and other factors, may also be considered.

MDI-SUP-I-051226

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MFS International Diversification Fund

For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes.

#### MFS International Large Cap Value Fund

#### Effective August 1, 2026, the name of MFS International Large Cap Value Fund will change to MFS International Value Fund.

#### Investment Objective
The fund's investment objective is to seek capital appreciation. The fund's objective may be changed without shareholder approval.

#### Principal Investment Strategies
MFS normally invests at least 80% of the fund's net assets in issuers with large market capitalizations.

MFS generally defines large market capitalization issuers as issuers with market capitalizations of at least $10 billion at the time of purchase. Issuers whose market capitalizations fall below this level after purchase continue to be considered to have a large market capitalization for purposes of the 80% policy.

#### Effective August 1, 2026, the two paragraphs directly above are restated in their entirety with the following paragraph:
MFS normally invests at least 80% of the fund's net assets in value companies. Value companies are companies that MFS believes are undervalued compared to their perceived worth in the marketplace. MFS considers a number of factors when determining whether a company is undervalued, including whether (i) the issuer is included in an index which is representative of value companies; (ii) the issuer is classified as a value company by an independent third party financial data provider and/or (iii) the issuer exhibits the characteristics of a value company, considering metrics such as historical and/or projected price-to-book, price-to-earnings, and price-to-cash flow ratios, enterprise value (the total value of the issuer's outstanding equity and debt) relative to earnings, and free cash flow yield compared to the applicable equity market and/or to issuers in the same sector or industry. In assessing the relative value of an issuer, MFS may also consider measures of financial quality, such as indicators of profitability (i.e., return on equity and return on invested capital), balance sheet strength (including leverage and interest coverage ratios), and capital allocation discipline. Value companies tend to have stock prices that are low relative to their earnings, dividends, assets, or other financial measures.

MFS normally invests the fund's assets primarily in foreign equity securities, including emerging market equity securities.

#### Effective August 1, 2026, the following paragraph is deleted in its entirety:
MFS focuses on investing the fund's assets in the stocks of companies that it believes are undervalued compared to their perceived worth (value companies). Value companies tend to have stock prices that are low relative to their earnings, dividends, assets, or other financial measures.

#### Effective August 1, 2026, the following sentence is added:
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 and their potential in light of their financial condition, and market, economic, political, and regulatory conditions. Factors considered may include analysis of an issuer's earnings, cash flows, competitive position, and management ability. MFS may also consider environmental, social, and governance (ESG) factors in its fundamental investment analysis where MFS believes such factors could materially impact the economic value of an issuer. ESG factors considered may include, but are not limited to, climate change, resource depletion, an issuer's governance structure and practices, data protection and privacy issues, and diversity and labor practices. Quantitative screening tools that systematically evaluate an issuer's valuation, price and earnings momentum, earnings quality, and other factors, may also be considered.

For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes.

#### MFS International New Discovery Fund

#### Investment Objective
The fund's investment objective is to seek capital appreciation. The fund's objective may be changed without shareholder approval.

#### Principal Investment Strategies
MFS normally invests the fund's assets primarily in foreign equity securities, including emerging market equity securities.

MFS focuses on investing the fund's assets in the stocks of companies it believes to have above average earnings growth potential compared to other companies (growth companies). Growth companies tend to have stock prices that are high relative to their earnings, dividends, book value, or other financial measures.

While MFS may invest the fund's assets in securities of companies of any size, MFS primarily invests in securities of companies with small to medium capitalizations.

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 and their potential in light of their financial condition, and market, economic, political, and regulatory conditions. Factors considered may include analysis of an issuer's earnings, cash flows, competitive position, and management ability. MFS may also consider environmental, social, and governance (ESG) factors in its fundamental investment analysis where MFS believes such factors could materially impact the economic value of an issuer. ESG factors considered may include, but are not limited to, climate change, resource depletion, an issuer's governance structure and practices, data protection and

MDI-SUP-I-051226

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MFS International Diversification Fund

privacy issues, and diversity and labor practices. Quantitative screening tools that systematically evaluate an issuer's valuation, price and earnings momentum, earnings quality, and other factors, may also be considered.

#### MFS Research International Fund

#### Investment Objective
The fund's investment objective is to seek capital appreciation. The fund's objective may be changed without shareholder approval.

#### Principal Investment Strategies
MFS normally invests the fund's assets primarily in foreign equity securities, including emerging market equity 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.

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.

In conjunction with a team of investment research analysts, sector leaders select investments for the fund. MFS generally manages the fund to be sector neutral to the MSCI EAFE (Europe, Australasia, Far East) Index using MFS' custom industry and sector categories to classify the fund and the MSCI EAFE (Europe, Australasia, Far East) Index's holdings.

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 and their potential in light of their financial condition, and market, economic, political, and regulatory conditions. Factors considered may include analysis of an issuer's earnings, cash flows, competitive position, and management ability. MFS may also consider environmental, social, and governance (ESG) factors in its fundamental investment analysis where MFS believes such factors could materially impact the economic value of an issuer. ESG factors considered may include, but are not limited to, climate change, resource depletion, an issuer's governance structure and practices, data protection and privacy issues, and diversity and labor practices. Quantitative screening tools that systematically evaluate an issuer's valuation, price and earnings momentum, earnings quality, and other factors, may also be considered.

MDI-SUP-I-051226

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