Summary Prospectus by Investment Company (Form 497K)

SUMMARY PROSPECTUS

April 30, 2026

MFS^® Global Tactical Allocation Portfolio

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 insurancefunds.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 April 30, 2026, as may be amended or supplemented from time to time, are incorporated by reference into this summary prospectus.

CLASS	TICKER SYMBOL
Initial Class	N/A
Service Class	N/A

Summary of Key Information

Investment Objective

The fund's investment objective is to seek total return.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares of the fund. If the fees and expenses imposed by the insurance company that issued your variable contracts or other eligible investor through which the fund is offered were included, your expenses would be higher.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
			Initial Class		Service Class
	Management Fee		0.74%		0.74%
	Distribution and/or Service (12b-1) Fees		None		0.25%
	Other Expenses		0.14%		0.14%
	Total Annual Fund Operating Expenses		0.88%		1.13%
	Fee Reductions and/or Expense Reimbursements1		(0.10)%		(0.10)%
	Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements		0.78%		1.03%

1 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 April 30, 2027. 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 0.76% of the class' average daily net assets annually for Initial Class shares and 1.01% of the class' average daily net assets annually for Service Class shares. ("Other Expenses" include 0.02% of interest and/or investment-related expenses incurred in connection with the fund's investment activity and/or foreign tax reclaim recovery expenses (including contingency fees and closing agreement expenses to be paid to third party service providers) incurred in connection with the fund's recovery of foreign taxes previously withheld in certain foreign countries. These expenses are excluded from the expense limitation described above.) This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least April 30, 2027.

WTS-SUM-043026

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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. If the fees and expenses imposed by the insurance company that issued your variable contracts or other eligible investor through which an investment in the fund is made were included, your expenses would be higher.

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:

			1 YEAR		3 YEARS		5 YEARS		10 YEARS
	Initial Class Shares		$80		$271		$478		$1,075
	Service Class Shares		$105		$349		$613		$1,366

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. 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 95% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser) seeks to achieve the fund's objective by generating returns from a combination of (1) individual security selection of a combination of debt instruments and equity securities and (2) a tactical asset allocation overlay primarily using derivative instruments to manage the fund's exposure to asset classes, markets and currencies. MFS expects to also use derivatives to seek to limit the fund's exposure to certain extreme market events if the fund's exposure to the equity security asset class, after taking into account the tactical overlay, is greater than 35% of the fund's assets. Derivatives include futures, forward contracts, options, and swaps.

The fund normally has exposure to at least three different countries and typically has significant long and/or short exposure to foreign securities and foreign currencies.

The fund's performance may not be correlated with the performance of the asset classes, markets, or currencies represented by the individual investments selected by MFS.

Individual Security Selection: In selecting direct investments for the fund, MFS normally invests the fund's assets in a combination of debt instruments and equity securities. Debt instruments include corporate debt instruments, U.S. Government securities, foreign government securities, securitized instruments (including mortgage-backed securities and other asset-backed securities), and other obligations to repay money borrowed. 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 invests approximately 65% of the fund's assets in debt instruments and cash and/or cash equivalents and approximately 35% of the fund's assets in equity securities. These asset class allocations are not designed to take advantage of short-term market opportunities and have been selected for investment over longer time periods. These asset class allocations may be changed without shareholder approval or notice. The actual asset class weightings can deviate due to market movements and cash flows. MFS periodically rebalances the fund's asset class weightings.

MFS invests the fund's assets in U.S. and foreign securities, including emerging market securities.

Of the fund's investments in debt instruments, 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.

While MFS may invest the equity portion of the fund's assets in securities of companies of any size, MFS primarily invests in securities of companies with large capitalizations.

Of the fund's investments in equity securities, MFS focuses on investing the fund's assets in the stocks of companies it believes are undervalued compared to their perceived worth (value companies).

While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives as part of its individual security selection process, 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 or currency exposure, or as alternatives to direct investments.

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 instruments. Quantitative models that systematically evaluate issuers and instruments are used by certain of the fund's equity securities portfolio managers and may also be considered by the fund's other portfolio managers.

Tactical Asset Allocation Overlay: MFS employs a top-down tactical asset allocation process primarily through the use of derivative instruments to adjust the fund's exposure to asset classes, markets, and currencies based on its assessment of the relative attractiveness of such asset classes, markets, and currencies. MFS manages the fund's exposure to asset classes, markets and currencies primarily based on its proprietary quantitative models. MFS may also consider current market conditions, its qualitative assessment of the risk/return characteristics of asset classes, markets, and/or currencies, and other factors in structuring the portfolio.

In managing the tactical overlay, MFS may increase or decrease the fund's exposure to asset classes, markets and/or currencies resulting from MFS' individual security selection based on MFS' assessment of the risk/return potential of such asset classes, markets and/or currencies. The fund's exposure to the equity security asset class, after taking into account the tactical overlay, may generally range from 0% to approximately 70% of the fund's assets.

Correspondingly, the fund's exposure to the debt instrument asset class after taking into account the tactical overlay may at times be as high as 100%. The fund's exposure to non-U.S. dollar currencies after taking into account the tactical overlay may generally range from 0% to approximately 50% of the fund's assets. MFS may also expose the fund to asset classes, markets and/or currencies that are not represented in the individual security selection component of the fund.

MFS may adjust the fund's net exposure to asset classes, markets and/or currencies by taking net short positions in an asset class, market or currency if MFS believes the risk/return potential of such asset class, market or currency is unattractive. Alternatively, MFS may cause the fund to take net long positions in an asset class, market or currency if MFS believes such asset class, market or currency appears attractive. When MFS' assessment of the relative

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attractiveness of asset classes and markets is neutral, the fund's exposure to the equity security asset class is expected to be approximately 35% of the fund's assets and the fund's exposure to the debt instrument and cash and/or cash equivalent asset classes is expected to be approximately 65% of the fund's assets.

After taking into account the tactical overlay, the fund may have significant exposure to issuers in a single sector, industry, country, or region.

MFS' tactical asset allocation process for the fund will typically make extensive use of derivatives.

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:

Allocation Risk: MFS' assessment of the risk/return potential of asset classes, markets and currencies, and its adjustments to the fund's exposure to asset classes, markets, and currencies 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.

Investment Strategy Risk: The fund's strategy to manage its exposure to asset classes, markets, and currencies may not produce the intended results. In addition, the strategies MFS may implement to limit the fund's exposure to certain extreme market events may not work as intended, and the costs associated with such strategies will reduce the fund's returns.

Investment Selection Risk: MFS' investment analysis, its development and use of quantitative models, 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. The quantitative models used by MFS (both proprietary and third-party) may not produce the intended results for a variety of reasons, including the factors used in the models, the weight placed on each factor in the models, changes from the market factors' historical trends, changing sources of market return or market risk, and technical issues in the design, development, implementation, application, and maintenance of the models (e.g., incomplete, stale, or inaccurate data, human error, programming or other software issues, coding errors, and technology failures).

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.

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.

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.

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,

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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.

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.

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.

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.

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 (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the insurance company that issued your variable contracts or other eligible investor through which an investment in the fund is made were included, they would reduce the returns shown.

Initial Class Bar Chart.

The total return for the three-month period ended March 31, 2026, was 1.58%. During the period(s) shown in the bar chart, the highest quarterly return was 7.99% (for the calendar quarter ended December 31, 2022) and the lowest quarterly return was (10.40)% (for the calendar quarter ended March 31, 2020).

Performance Table.

Average Annual Total Returns
(For the Periods Ended December 31, 2025)

			1 YEAR		5 YEARS		10 YEARS
	Initial Class Shares		15.48%		4.86%		5.67%
	Service Class Shares		15.21%		4.60%		5.40%
	Index Comparisons (Reflects no deduction for fees, expenses, or taxes)
	Bloomberg Global Aggregate Index		8.17%		(2.15)%		1.26%
	MFS Global Tactical Allocation Blended Index		10.78%		4.20%		5.81%

As of December 31, 2025, the MFS Global Tactical Allocation Blended Index (the Blended Index) consisted of the following indices and weightings: 35% MSCI World Index (net div); 54% Bloomberg Global Aggregate Index (USD Hedged); and 11% Bloomberg Global Aggregate Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.

Investment Adviser

MFS serves as the investment adviser for the fund.

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Portfolio Manager(s)

Portfolio Manager	Since	Title
Pilar Gomez-Bravo	2013	Co-Chief Investment Officer-Global Fixed Income of MFS
Steven Gorham	2000	Investment Officer of MFS
Andy Li	2019	Investment Officer of MFS
John Mitchell	2023	Investment Officer of MFS
Johnathan Munko	2021	Investment Officer of MFS
Benjamin Nastou	2010	Investment Officer and Chief Investment Officer-Quantitative Solutions of MFS
Jonathan Sage	2015	Investment Officer of MFS
Natalie Shapiro	2010	Investment Officer of MFS
Erich Shigley	2021	Investment Officer of MFS
David Shindler	2022	Investment Officer of MFS
Robert Spector	2015	Investment Officer of MFS
Erik Weisman	2004	Investment Officer of MFS

Purchase and Sale of Fund Shares

You should consult with the insurance company that issued your variable contract, or other eligible investor through which your investment in the fund is made, for minimum investment requirements and redemption procedures.

Taxes

You should consult with the insurance company that issued your variable contract, or other eligible investor through which your investment in the fund is made, to understand the tax treatment of your investment.

Payments to Financial Intermediaries

The fund, MFS, and/or its affiliates may make payments to insurance companies, other financial intermediaries, and all of their affiliates, for distribution and/or other services. These payments may create a conflict of interest for the insurance company or other financial intermediary to include the fund as an investment option in its product or to recommend the fund over another investment option. Ask your financial intermediary or insurance company, or visit your financial intermediary's or insurance company's website, for more information.

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