The report is prepared for the general information of shareholders. It is authorized for distribution to prospective investors only when preceded or accompanied by a current prospectus.

LETTER FROM THE EXECUTIVE CHAIR

Dear Shareholders:

Markets experienced dramatic swings in early 2020 as the coronavirus pandemic brought the global economy to a standstill for several months. Optimism over the

development of vaccines and therapeutics, along with a decline in cases in countries affected by the outbreak early on, brightened the economic and market outlook during the second quarter, as did the phased reopening of U.S. states. However, a great deal of uncertainty remains. While policymakers and public health officials have learned a great deal about combating the virus, much remains unknown at a time when the risks are rising for a second wave of infection. Political uncertainty is heightened as well, as the pandemic has caused many jurisdictions in the United States to adopt mail-in voting for the first time, raising questions over whether ballots in the November elections will be counted as quickly as they have been in the past.

Global central banks have taken aggressive steps to cushion the economic and market fallout related to the virus, and governments are deploying unprecedented levels of fiscal support, though in the United States some of those measures were allowed to lapse at the end of July as negotiators found themselves at an impasse over the scope of additional funding. The measures already put in place have helped build a supportive environment and are encouraging economic recovery; however, if markets disconnect from fundamentals, they can also sow the seeds of instability. In the aftermath of the crisis, societal changes may be likely, as households, businesses, and governments adjust to a new reality, and any such alterations could affect the investment landscape. For investors, events such as the COVID-19 outbreak demonstrate the importance of having a deep understanding of company fundamentals, and we have built our global research platform to do just that.

Here at MFS®, we aim to help our clients navigate the growing complexity of the markets and world economies. Our long-term investment philosophy and commitment to the responsible allocation of capital allow us to tune out the noise and uncover what we believe are the best, most durable investment opportunities in the market. Through our unique global investment platform, we combine collective expertise, thoughtful risk management, and long-term discipline to create sustainable value for investors.

Respectfully,

Robert J. Manning

Executive Chair

MFS Investment Management

October 19, 2020

The opinions expressed in this letter are subject to change and may not be relied upon for investment advice. No forecasts can be guaranteed.

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PORTFOLIO COMPOSITION

Cash & Cash Equivalents includes any cash, investments in money market funds, short-term securities, and other assets less liabilities. Please see the Statement of Assets and Liabilities for additional information related to the fund’s cash position and other assets and liabilities.

Percentages are based on net assets as of August 31, 2020.

The portfolio is actively managed and current holdings may be different.

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MANAGEMENT REVIEW

Summary of Results

For the twelve months ended August 31, 2020, Class A shares of the MFS Core Equity Fund (fund) provided a total return of 20.59%, at net asset value. This compares with a return of 21.44% for the fund’s benchmark, the Russell 3000® Index.

Market Environment

Markets experienced an extraordinarily sharp selloff and in many cases an unusually rapid recovery late in the period. Central banks and fiscal authorities undertook astonishing levels of stimulus to offset the economic effects of government-imposed social-distancing measures implemented to slow the spread of the COVID-19 virus. At this point, the global economy looks to have experienced the deepest, steepest, and possibly shortest recession in the postwar period. However, the recovery remains subject to more than the usual number of uncertainties due to questions about the evolution of the virus, what its continued impact will be and when vaccines or medicines will become available to prevent or treat it.

Compounding market uncertainty earlier in the pandemic was a crash in the price of crude oil due to a sharp drop in global demand and a disagreement between Saudi Arabia and Russia over production cuts, which resulted in a price war. The subsequent decline in prices undercut oil exporters, many of which are in emerging markets, as well as a large segment of the high-yield credit market. The OPEC+ group later agreed on output cuts, with shale oil producers in the United States also decreasing production, which – along with the gradual reopening of some major economies and the resultant boost in demand – helped stabilize the price of crude oil.

Around the world, central banks responded quickly and massively to the crisis with programs to improve liquidity and support markets. These programs proved largely successful in helping to restore market function, ease volatility and stimulate a continued market rebound. Late in the period, the US Federal Reserve adopted a new, flexible average-inflation-targeting framework, which is expected to result in policy rates remaining at low levels for longer. In developed countries, monetary easing measures were complemented by large fiscal stimulus initiatives, although late in the period there was uncertainty surrounding the timing and scope of additional US recovery funding. Due to relatively manageable external liabilities and balances of payments in many countries, along with persistently low inflation, even emerging market countries were able to implement countercyclical policies – a departure from the usual market-dictated response to risk-off crises.

As has often been the case in a crisis, market vulnerabilities have been revealed. For example, companies that have added significant leverage to their balance sheets in recent years by borrowing to fund dividend payments and stock buybacks have in many cases halted share repurchases and cut dividends, and some firms have been forced to recapitalize.

Detractors from Performance

Security selection in both the capital goods and health care sectors detracted from performance relative to the Russell 3000® Index. Within the capital goods sector, not

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Management Review – continued

owning shares of electric vehicle manufacturer Tesla hurt relative results. The share price of Tesla rose during the period on the back of solid earnings and better-than-anticipated free cash flow. Additionally, the firm disclosed record deliveries amid the launch of its Model Y and China factory, despite weak near-term demand for autos during the initial stages of the pandemic. Within the health care sector, there were no individual stocks that were among the fund’s top relative detractors for the reporting period.

Elsewhere, not owning shares of computer graphics processor maker NVIDIA and digital payment technology developer PayPal held back relative returns. The share price of NVIDIA advanced as the company reported solid earnings, primarily driven by strength in gaming and robust demand for Data Center products. The timing of the fund’s ownership in shares of semiconductor company Intel also dampened relative performance. The share price of Intel suffered in the second half of the reporting period, mainly due to major delays with its 7nm process technology. Additionally, overweight positions in real estate investment trust EPR Properties, integrated energy company Chevron, financial services provider Charles Schwab, banking services provider Truist Financial and financial services company U.S. Bancorp further weighed on relative results.

The fund’s cash and/or cash equivalents position during the period was also a detractor from relative performance. Under normal market conditions, the fund strives to be fully invested and generally holds cash to buy new holdings and to provide liquidity. In a period when equity markets rose, as measured by the fund’s benchmark, holding cash hurt performance versus the benchmark, which has no cash position.

Contributors to Performance

Security selection in both the technology and consumer cyclicals sectors contributed to relative performance. Within the technology sector, the fund’s overweight positions in computer and personal electronics maker Apple, customer information software manager salesforce.com and software company Adobe Systems, and holdings of analytics services provider Clarivate ^(b), boosted relative performance. Despite supply constraints for both the Apple Watch and Apple Airpods Pro, the share price of Apple was supported by stronger-than-anticipated revenues, driven by robust demand in its wearable technology and services segments paired with strong iPhone sales. Within the consumer cyclicals sector, an overweight position in internet retailer Amazon.com supported relative performance. The share price of Amazon.com benefited from strong e-commerce volumes as consumers adjusted to global lockdowns in response to the COVID-19 pandemic. As a result, the company reported revenues ahead of expectations, partially offset by additional COVID-related operating costs.

Elsewhere, not owning shares of integrated oil and gas company Exxon Mobil, global financial services firm JPMorgan Chase and telecommunication services provider AT&T bolstered relative returns. The share price of Exxon Mobil fell during the period after the company missed consensus estimates on the back of disappointing chemical and refining margins and higher costs. Furthermore, oil and gas prices came under significant pressure due to lower demand from disruptions caused by the COVID-19 virus and the price war between Saudi Arabia and Russia. Additionally, an underweight

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Management Review – continued

position in aerospace company Boeing ^(h), and the timing of the fund’s ownership in shares of diversified financial services firm Wells Fargo, aided relative results.

Respectfully,

Portfolio Manager(s)

Joseph MacDougall

The views expressed in this report are those of the portfolio manager(s) only through the end of the period of the report as stated on the cover and do not necessarily reflect the views of MFS or any other person in the MFS organization. These views are subject to change at any time based on market or other conditions, and MFS disclaims any responsibility to update such views. These views may not be relied upon as investment advice or an indication of trading intent on behalf of any MFS portfolio. References to specific securities are not recommendations of such securities, and may not be representative of any MFS portfolio’s current or future investments.

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PERFORMANCE SUMMARY THROUGH 8/31/20

The following chart illustrates a representative class of the fund’s historical performance in comparison to its benchmark(s). Performance results include the deduction of the maximum applicable sales charge and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. The performance of other share classes will be greater than or less than that of the class depicted below. Benchmarks are unmanaged and may not be invested in directly. Benchmark returns do not reflect sales charges, commissions or expenses. (See Notes to Performance Summary.)

Performance data shown represents past performance and is no guarantee of future results. Investment return and principal value fluctuate so your shares, when sold, may be worth more or less than the original cost; current performance may be lower or higher than quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on fund distributions or the redemption of fund shares.

Growth of a Hypothetical $10,000 Investment

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Performance Summary – continued

Total Returns through 8/31/20

Average annual without sales charge

CDSC – Contingent Deferred Sales Charge.

Class I, R1, R2, R3, R4, and R6 shares do not have a sales charge.

Benchmark Definition(s)

Russell 3000® Index – constructed to provide a comprehensive barometer for the 3,000 largest U.S. companies based on total market capitalization, which represents approximately 98% of the investable U.S. equity market. Frank Russell Company (“Russell”) is the source and owner of the trademarks, service marks, and copyrights related to the Russell Indexes. Russell® is a trademark of Frank Russell Company. Neither Russell nor its licensors accept any liability for any errors or omissions in the Russell Indexes and/or Russell ratings or underlying data and no party may rely on any Russell Indexes and/or Russell ratings and/or underlying data contained in this document. No further distribution of Russell Data is permitted without Russell’s express written consent. Russell does not promote, sponsor, or endorse the content of this document.

It is not possible to invest directly in an index.

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Performance Summary – continued

Notes to Performance Summary

Average annual total return represents the average annual change in value for each share class for the periods presented. Life returns are presented where the share class has less than 10 years of performance history and represent the average annual total return from the class inception date to the stated period end date. As the fund’s share classes may have different inception dates, the life returns may represent different time periods and may not be comparable. As a result, no comparative benchmark performance information is provided for life periods.

Performance results reflect any applicable expense subsidies and waivers in effect during the periods shown. Without such subsidies and waivers the fund’s performance results would be less favorable. Please see the prospectus and financial statements for complete details.

Performance results do not include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles and may differ from amounts reported in the financial highlights.

From time to time the fund may receive proceeds from litigation settlements, without which performance would be lower.

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EXPENSE TABLE

Fund expenses borne by the shareholders during the period,

March 1, 2020 through August 31, 2020

As a shareholder of the fund, you incur two types of costs: (1) transaction costs, including sales charges (loads) on certain purchase or redemption payments, and (2) ongoing costs, including management fees; distribution and service (12b-1) fees; and other fund expenses. This example is intended to help you understand your ongoing costs (in dollars) of investing in the fund and to compare these costs with the ongoing costs of investing in other mutual funds.

The example is based on an investment of $1,000 invested at the beginning of the period and held for the entire period March 1, 2020 through August 31, 2020.

Actual Expenses

The first line for each share class in the following table provides information about actual account values and actual expenses. You may use the information in this line, together with the amount you invested, to estimate the expenses that you paid over the period. Simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number in the first line under the heading entitled “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

Hypothetical Example for Comparison Purposes

The second line for each share class in the following table provides information about hypothetical account values and hypothetical expenses based on the fund’s actual expense ratio and an assumed rate of return of 5% per year before expenses, which is not the fund’s actual return. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period. You may use this information to compare the ongoing costs of investing in the fund and other funds. To do so, compare this 5% hypothetical example with the 5% hypothetical examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown in the table are meant to highlight your ongoing costs only and do not reflect any transactional costs, such as sales charges (loads). Therefore, the second line for each share class in the table is useful in comparing ongoing costs only, and will not help you determine the relative total costs of owning different funds. In addition, if these transactional costs were included, your costs would have been higher.

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Expense Table – continued

Notes to Expense Table

Expense ratios include 0.02% of investment related expenses from short sales (See Note 2 of the Notes to Financial Statements). Each class with a Rule 12b-1 service fee is subject to a rebate of a portion of such fee. Such rebates are included in the expense ratios above. For Class A and Class R2 shares, this rebate reduced the expense ratios above by 0.01%. See Note 3 in the Notes to Financial Statements for additional information.

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