Summary Prospectus by Investment Company - Form 497K

SUMMARY PROSPECTUS

August 28, 2024

MFS^® Core Bond Fund

Before you invest, you may want to review the fund's prospectus, which contains more information about the fund and its risks. You can find the fund's prospectus and other information about the fund, including the fund's reports to shareholders and statement of additional information, online at funds.mfs.com. You can also get this information at no cost by calling 1-800-225-2606 or by sending an e-mail request to [email protected]. The fund's prospectus and statement of additional information, both dated August 28, 2024, as may be amended or supplemented from time to time, are incorporated by reference into this summary prospectus.

CLASS	TICKER SYMBOL
Class A	MCBEX
Class C	MCBCX
Class I	MCBFX
Class R1	MCBGX
Class R2	MCBHX
Class R3	MCBJX
Class R4	MCBKX
Class R6	MCBMX

Summary of Key Information

Investment Objective

The fund's investment objective is to seek total return with an emphasis on current income, but also considering 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 $100,000 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 11 and "Appendix A - Waivers and Reductions of Sales Charges" on page A-1 of the fund's prospectus.

Shareholder Fees (fees paid directly from your investment):

Share Class

A

C

I

R1

R2

R3

R4

R6

Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)

4.25%

None

None

None

None

None

None

None

Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)

1.00%#

1.00%

None

None

None

None

None

None

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
	Share Class		A			C		I		R1		R2		R3		R4		R6
	Management Fee		0.33%			0.33%		0.33%		0.33%		0.33%		0.33%		0.33%		0.33%
	Distribution and/or Service (12b-1) Fees		0.25%			1.00%		None		1.00%		0.50%		0.25%		None		None
	Other Expenses		0.70%			0.70%		0.70%		0.70%		0.70%		0.70%		0.70%		0.67%
	Total Annual Fund Operating Expenses		1.28%			2.03%		1.03%		2.03%		1.53%		1.28%		1.03%		1.00%
	Fee Reductions and/or Expense Reimbursements1		(0.64)%			(0.64)%		(0.64)%		(0.64)%		(0.64)%		(0.64)%		(0.64)%		(0.67)%
	Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements		0.64%			1.39%		0.39%		1.39%		0.89%		0.64%		0.39%		0.33%

#This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.

1Massachusetts 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 August 31, 2025. MFS has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, certain tax reclaim recovery expenses (including contingency fees and closing agreement expenses), and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity), such that "Total Annual Fund Operating Expenses" do not exceed 0.64% of the class' average daily net assets annually for each of Class A and Class R3 shares, 1.39% of the class' average daily net assets annually for each of Class C and Class R1 shares, 0.39% of the class' average daily net assets annually for each of Class I and Class R4 shares, 0.89% of the class' average daily net assets annually for Class R2 shares, and 0.33% of the class' average daily net assets annually for Class R6 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2025.

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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 (unless otherwise indicated); 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:

			1 YEAR		3 YEARS		5 YEARS		10 YEARS
	Class A Shares		$488		$753		$1,039		$1,851
	Class C Shares assuming1
	redemption at end of period		$242		$575		$1,034		$2,113
	no redemption at end of period		$142		$575		$1,034		$2,113
	Class I Shares		$40		$264		$506		$1,201
	Class R1 Shares		$142		$575		$1,034		$2,307
	Class R2 Shares		$91		$421		$774		$1,769
	Class R3 Shares		$65		$343		$641		$1,489
	Class R4 Shares		$40		$264		$506		$1,201
	Class R6 Shares		$34		$252		$487		$1,164

1Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.

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 100% of the average value of its portfolio (53% excluding to be announced (TBA) transactions).

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 debt instruments.

Debt instruments include corporate bonds, U.S. Government securities, securitized instruments (including mortgage-backed securities and other asset-backed securities), and other obligations to repay money borrowed.

MFS generally invests substantially all of the fund's assets in investment grade quality debt instruments.

MFS may purchase or sell securities for the fund on a when-issued, delayed delivery, or forward commitment basis where payment and delivery take place at a future settlement date, including mortgage-backed securities purchased or sold in the to be announced (TBA) market.

MFS may invest the fund's assets in foreign securities.

MFS normally invests the fund's assets across different industries and sectors, but MFS may invest a significant percentage of the fund's assets in issuers in a single industry or sector.

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.

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

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:

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.

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.

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

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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.

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.

When-Issued, Delayed Delivery, and Forward Commitment Transaction Risk: The purchaser in a when-issued, delayed delivery or forward commitment transaction assumes the rights and risks of ownership, including the risks of price and yield fluctuations and the risk that the security will not be issued or delivered as anticipated. When-issued, delayed delivery, and forward commitment transactions can involve leverage. TBA transactions may significantly increase the fund's portfolio turnover rate.

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.

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 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. Updated performance is available online at mfs.com or by calling 1-800-225-2606.

Class A 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 total return for the six-month period ended June 30, 2024, was (0.37)%. During the period(s) shown in the bar chart, the highest quarterly return was 6.69% (for the calendar quarter ended December 31, 2023) and the lowest quarterly return was (3.02)% (for the calendar quarter ended September 30, 2023).

Performance Table.

Average Annual Total Returns
(For the Periods Ended December 31, 2023)

	Share Class		1 YEAR		LIFE (INCEPTION 6-22-2022)
	Returns Before Taxes
	C Shares		4.39%		1.83%
	I Shares		6.54%		2.85%
	R1 Shares		5.39%		1.83%
	R2 Shares		5.90%		2.33%
	R3 Shares		6.17%		2.59%
	R4 Shares		6.43%		2.85%
	R6 Shares		6.46%		2.86%
	A Shares		1.56%		(0.35)%
	Returns After Taxes on Distributions
	A Shares		(0.22)%		(2.00)%
	Returns After Taxes on Distributions and Sale of Fund Shares
	A Shares		0.89%		(0.97)%
	Index Comparison (Reflects no deduction for fees, expenses, or taxes)
	Bloomberg U.S. Aggregate Bond Index		5.53%		2.65%

After-tax returns are calculated using the historical highest individual 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

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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.

Investment Adviser

MFS serves as the investment adviser for the fund.

Portfolio Manager(s)

Portfolio Manager	Since	Title
Alexander Mackey	2022	Co-Chief Investment Officer-Global Fixed Income of MFS
Joshua Marston	2022	Investment Officer of MFS

Purchase and Sale of Fund Shares

You may purchase and redeem shares of the fund each day the New York Stock Exchange (the NYSE) is open for trading. You may purchase or redeem shares either by having your financial intermediary process your purchase or redemption, or through MFS Service Center, Inc. (MFSC) by overnight mail (MFSC, Suite 219341, 430 W 7^th Street, Kansas City, MO 64105-1407), by mail ([Fund Name], P.O. Box 219341, Kansas City, MO 64121-9341), by telephone (1-800-225-2606), or via the Internet at mfs.com (MFS Access).

The fund's initial and subsequent investment minimums generally are as follows:

Class	Initial Minimum	Subsequent Minimum
Class A, Class C	None - automatic investment plans and certain asset-based fee programs $25 - employer-sponsored retirement plans $250 - Traditional and Roth IRAs $1,000 - other accounts	$50 - by check and non-systematic written exchange request, and via MFSC telephone representatives None - other purchases
Class I, Class R1, Class R2, Class R3, Class R4, Class R6	None	None

Purchases of Class R1 and Class R2 shares are closed to new eligible investors. Existing eligible investors can make additional purchases and reinvest distributions in Class R1 and Class R2 shares in any account open. Existing eligible investors may also exchange their Class R1 and Class R2 shares for the same share class of another MFS fund, open new Class R1 and Class R2 share accounts in other MFS funds, or transfer some or all of the shares in their account to another account and such account will be treated as an open account. Subject to the approval of the fund's Board of Trustees, the fund may in the future (i) close purchases of Class R1 and/or Class R2 shares to existing eligible investors; (ii) terminate and liquidate Class R1 and/or Class R2 shares; or (iii) convert Class R1 and/or Class R2 shares to another share class of the fund. Such actions may be undertaken without shareholder approval, but the fund expects to provide shareholders with at least 60 days' notice before taking any such action.

Taxes

If your shares are held in a taxable account, the fund's distributions will be taxed to you as ordinary income and/or capital gains. If your shares are held in a tax-advantaged account, you will generally be taxed only upon withdrawals from the account.

Payments to Broker/Dealers and Other Financial Intermediaries

If you purchase shares of the fund through a broker/dealer or other financial intermediary (such as a bank), the fund, MFS, and/or MFS' affiliates may pay the financial intermediary for the sale of shares of the fund and/or the servicing of shareholder accounts. These payments may create a conflict of interest by influencing your broker/dealer or other financial intermediary and your salesperson to recommend the fund over another investment. Ask your financial intermediary or visit your financial intermediary's website for more information.

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