AUG    ^08.31.20

ANNUAL REPORT

AB ALL MARKET TOTAL RETURN PORTFOLIO

Beginning January 1, 2021, as permitted by new regulations adopted by the Securities and Exchange Commission, the Fund’s annual and semi-annual shareholder reports will no longer be sent by mail, unless you specifically request paper copies of the reports. Instead, the reports will be made available on a website, and you will be notified by mail each time a report is posted and provided with a website address to access the report.

If you already elected to receive shareholder reports electronically, you will not be affected by this change and you need not take any action. You may elect to receive shareholder reports and other communications from the Fund electronically at any time by contacting your financial intermediary (such as a broker-dealer or bank) or, if you are a direct investor, by calling the Fund at (800) 221 5672.

You may elect to receive all future reports in paper form free of charge. If you invest through a financial intermediary, you can contact your financial intermediary to request that you continue to receive paper copies of your shareholder reports; if you invest directly with the Fund, you can call the Fund at (800) 221 5672. Your election to receive reports in paper form will apply to all funds held in your account with your financial intermediary or, if you invest directly, to all AB Mutual Funds you hold.

Investors should consider the investment objectives, risks, charges and expenses of the Fund carefully before investing. For copies of our prospectus or summary prospectus, which contain this and other information, visit us online at www.abfunds.com or contact your AB representative. Please read the prospectus and/or summary prospectus carefully before investing.

This shareholder report must be preceded or accompanied by the Fund’s prospectus for individuals who are not current shareholders of the Fund.

You may obtain a description of the Fund’s proxy voting policies and procedures, and information regarding how the Fund voted proxies relating to portfolio securities during the most recent 12-month period ended June 30, without charge. Simply visit AB’s website at www.abfunds.com, or go to the Securities and Exchange Commission’s (the “Commission”) website at www.sec.gov, or call AB at (800) 227 4618.

The Fund files its complete schedule of portfolio holdings with the Commission for the first and third quarters of each fiscal year as an exhibit to its reports on Form N-PORT. The Fund’s Form N-PORT reports are available on the Commission’s website at www.sec.gov. The Fund’s Forms N-PORT may also be reviewed and copied at the Commission’s Public Reference Room in Washington, DC; information on the operation of the Public Reference Room may be obtained by calling (800) SEC 0330. AB publishes full portfolio holdings for the Fund monthly at www.abfunds.com.

AllianceBernstein Investments, Inc. (ABI) is the distributor of the AB family of mutual funds. ABI is a member of FINRA and is an affiliate of AllianceBernstein L.P., the Adviser of the funds.

The [A/B] logo is a registered service mark of AllianceBernstein and AllianceBernstein^® is a registered service mark used by permission of the owner, AllianceBernstein L.P.

FROM THE PRESIDENT

Dear Shareholder,

We are pleased to provide this report for AB All Market Total Return Portfolio (the “Fund”). Please review the discussion of Fund performance, the market conditions during the reporting period and the Fund’s investment strategy.

As always, AB strives to keep clients ahead of what’s next by:

Whether you’re an individual investor or a multi-billion-dollar institution, we put knowledge and experience to work for you.

AB’s global research organization connects and collaborates across platforms and teams to deliver impactful insights and innovative products. Better insights lead to better opportunities—anywhere in the world.

For additional information about AB’s range of products and shareholder resources, please log on to www.abfunds.com.

Thank you for your investment in the AB Mutual Funds.

Sincerely,

Robert M. Keith

President and Chief Executive Officer, AB Mutual Funds

ANNUAL REPORT

October 14, 2020

This report provides management’s discussion of fund performance for AB All Market Total Return Portfolio for the annual reporting period ended August 31, 2020.

The Fund’s investment objective is to achieve the highest total return consistent with the Adviser’s determination of reasonable risk.

INVESTMENT RESULTS

The table above shows the Fund’s performance compared to its primary benchmark, the Morgan Stanley Capital International All Country World Index (“MSCI ACWI”) (net), and the Bloomberg Barclays Global Aggregate Bond Index (USD hedged), for the six- and 12-month periods ended August 31, 2020.

All share classes of the Fund underperformed the primary benchmark for both the six- and 12-month periods. All share classes underperformed the Bloomberg Barclays Global Aggregate Bond Index (USD hedged) for the 12-month period, but outperformed for the six-month period, all before sales charges.

During both periods, equity markets performed well, and therefore, the Fund’s more diversified approach, which balances exposures to equities, bonds, commodities and alternative strategies, underperformed the

all-equity benchmark. Overall allocations within equities contributed to absolute performance. Allocations within fixed-income assets contributed for the 12-month period, but detracted for the six-month period; alternative strategies detracted for the 12-month period, but contributed for the six-month period. Security selection within all three asset classes detracted over both periods.

The Fund utilized derivatives for hedging and investment purposes in the form of futures, inflation Consumer Price Index swaps and purchased options, which contributed to absolute performance for both periods, while credit default swaps, interest rate swaps, total return swaps, variance swaps and written options detracted; currency forwards detracted for the six-month period, but contributed for the 12-month period; purchased swaptions contributed for the six-month period, but detracted for the 12-month period.

MARKET REVIEW AND INVESTMENT STRATEGY

Global equity markets, led by a strong US rally, recorded positive returns for the 12-month period ended August 31, 2020. US, international and emerging-market equities erased losses from March when the COVID-19 pandemic triggered a decline from all-time highs as global economies were shuttered amid stay-at-home mandates. Investor optimism was supported by expanded monetary and fiscal stimulus, signs of encouraging economic data, and news that several potential vaccines had reached advanced trials. Despite the widespread rebound, headwinds from a resurgence of US-China tensions, persistently high rates of COVID-19 cases in many countries and an unprecedented contraction of economic growth threatened to temper the acceleration of economic activity. In the US, growth stocks consistently outperformed value stocks in all categories. Small-cap stocks continued to rally, outperforming large-caps at times; however, overall, large-cap stocks have performed significantly better.

Global fixed-income market returns were positive yet volatile over the 12-month period. Central banks and governments enacted an unprecedented amount of monetary and fiscal stimulus to combat market illiquidity and cushion the negative economic impact of COVID-19, which set the stage for a rebound in risk assets following the sell-off that started in March. Government bonds rallied as interest rates were slashed. Emerging- and developed-market investment-grade and high-yield corporate bonds led gains as investors searched for higher yields in a period of falling interest rates. Securitized assets advanced, while emerging-market sovereign and local bonds also ended the period with positive returns. The US dollar fell against all major developed-market currencies and was mixed against emerging-market currencies.

The Fund’s Senior Investment Management Team (the “Team”) strives to provide the highest total return consistent with reasonable risk. The

Team’s global multi-asset strategy focuses on growth and defensively managing market volatility. The Team utilizes a rigorous quantitative research toolset with fundamental expertise across all regions and markets.

INVESTMENT POLICIES

The Adviser allocates the Fund’s investments primarily among a number of asset classes, including equity securities, fixed-income securities, and a number of alternative asset classes and alternative investment strategies. The Fund pursues a global strategy, typically investing in securities of issuers located in the United States and in other countries throughout the world, including emerging-market countries. Under normal circumstances, at least 40% of the Fund’s net assets will be invested in securities of non-US issuers.

The Fund’s investments in equity securities of issuers consist primarily of securities of large-capitalization companies, but include securities of small- and mid-capitalization companies to a lesser extent, and include derivatives related to equity securities. In selecting equity securities for the Fund, the Adviser uses fundamental and quantitative analysis with the goal of generating returns primarily from security selection rather than price movements in equity securities generally. Fixed-income securities include corporate and sovereign debt securities as well as interest rate derivatives and credit derivatives such as credit default swaps. Fixed-income securities also include debt securities with lower credit ratings (commonly known as “junk bonds”). In selecting fixed-income securities for the Fund, the Adviser attempts to take advantage of inefficiencies that it believes exist in the global fixed-income markets. These inefficiencies arise from investor behavior, market complexity and the investment limitations to which investors are subject.

Alternative investments include various instruments the returns on which are expected to have low correlation with returns on equity and fixed-income securities, such as commodities and related derivatives, real estate-related securities and inflation-indexed securities. Alternative investment strategies that may be pursued by the Fund directly or indirectly through investment in other registered investment companies include (i) long/short equity strategies through which the Fund takes long positions in certain securities in the expectation that they will increase in value and takes short positions in other securities in the expectation that they will decrease in value; (ii) strategies that consider macroeconomic and technical factors to identify and exploit opportunities across global asset classes; and (iii) event-driven strategies that invest in the securities of companies that are expected to

(continued on next page)

become the subject of major corporate events and companies in which an active role in company management has been taken or sought by a third-party investor.

The Adviser adjusts the Fund’s asset class exposure utilizing both fundamental analysis and the Adviser’s Dynamic Asset Allocation (“DAA”) approach. DAA comprises a series of analytical and forecasting tools employed by the Adviser to gauge fluctuations in the risk/return profile of various asset classes. DAA seeks to adjust the Fund’s investment exposure in changing market conditions and thereby reduce overall portfolio volatility by mitigating the effects of market fluctuations, while preserving consistent long-term return potential. For example, the Adviser may seek to reduce the Fund’s risk exposure to one or more assets classes when DAA suggests that market risks relevant to those asset classes are rising but return opportunities are declining. In addition to merely increasing or decreasing asset class exposure by buying or selling securities of that asset class, the Adviser may pursue DAA implementation for the Fund by utilizing derivatives.

The Adviser intends to utilize a variety of derivatives in its management of the Fund. As noted above, the Adviser may use derivatives to gain exposure to various asset classes, and may cause the Fund to enter into derivatives in making the adjustments called for by DAA. As a result of the use of derivatives, the Fund will frequently be leveraged, with net investment exposure substantially in excess of net assets.

While the Fund may seek to gain exposure to physical commodities traded in the commodities markets through investments in a variety of derivative instruments, the Adviser expects that the Fund seeks to gain such exposure to commodities and commodities-related instruments and derivatives primarily through investments in AB All Market Total Return Portfolio (Cayman), Ltd., a wholly-owned subsidiary of the Fund organized under the laws of the Cayman Islands (the “Subsidiary”). The Subsidiary is advised by the Adviser and has the same investment objective and substantially similar investment policies and restrictions as the Fund except that the Subsidiary, unlike the Fund, may invest, without limitation, in commodities and commodities-related instruments. The Fund is subject to the risks associated with the commodities, derivatives and other instruments in which the Subsidiary invests, to the extent of its investment in the Subsidiary. The Fund limits its investment in the Subsidiary to no more than 25% of its total assets. Investment in the Subsidiary is expected to provide the Fund with commodity exposure within the limitations of federal tax requirements that apply to the Fund.

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Currency exchange rate fluctuations can have a dramatic impact on returns. The Fund’s foreign currency exposures will come from investment in securities priced or denominated in foreign currencies and from direct holdings in foreign currencies and currency-related derivatives. The Adviser may seek to hedge all or a portion of the currency exposure resulting from Fund investments or decide not to hedge this exposure. The Adviser may seek investment opportunities by taking long or short positions in currencies through the use of currency-related derivatives.

DISCLOSURES AND RISKS

Benchmark Disclosure

All indices are unmanaged and do not reflect fees and expenses associated with the active management of a mutual fund portfolio. The MSCI ACWI (net, free float-adjusted, market capitalization weighted) represents the equity market performance of developed and emerging markets. The Bloomberg Barclays Global Aggregate Bond Index (USD hedged) represents the performance of global investment-grade developed fixed-income markets, hedged to the US dollar. MSCI makes no express or implied warranties or representations, and shall have no liability whatsoever with respect to any MSCI data contained herein. The MSCI data may not be further redistributed or used as a basis for other indices, any securities or financial products. This report is not approved, reviewed or produced by MSCI. Net returns include the reinvestment of dividends after deduction of non-US withholding tax. An investor cannot invest directly in an index or average, and their results are not indicative of the performance for any specific investment, including the Fund.

A Word About Risk

Market Risk: The value of the Fund’s assets will fluctuate as the stock, bond or commodities markets fluctuate. The value of its investments may decline, sometimes rapidly and unpredictably, simply because of economic changes or other events, including public health crises (including the occurrence of a contagious disease or illness), that affect large portions of the market. It includes the risk that a particular style of investing, such as growth or value, may be underperforming the stock market generally.

Allocation Risk: The allocation of investments among different investment styles, such as equity or debt, growth or value, US or non-US securities, or diversification strategies, may have a more significant effect on the Fund’s net asset value (“NAV”) when one of these investments is performing more poorly than another.

Credit Risk: An issuer or guarantor of a fixed-income security, or the counterparty to a derivatives or other contract, may be unable or unwilling to make timely payments of interest or principal, or to otherwise honor its obligations. The issuer or guarantor may default, causing a loss of the full principal amount of a security and accrued interest. The degree of risk for a particular security may be reflected in its credit rating. There is the possibility that the credit rating of a fixed-income security may be downgraded after purchase, which may adversely affect the value of the security. Investments in fixed-income securities with lower ratings (commonly known as “junk bonds”) are subject to a higher probability that an issuer will default or fail to meet its payment obligations.

DISCLOSURES AND RISKS (continued)

High-Yield Debt Securities Risk: Investments in fixed-income securities with lower ratings (commonly known as “junk bonds”) tend to have a higher probability that an issuer will default or fail to meet its payment obligations. These securities may be subject to greater price volatility due to such factors as specific corporate developments, interest-rate sensitivity, negative perceptions of the junk bond market generally and less secondary market liquidity.

Interest-Rate Risk: Changes in interest rates will affect the value of the Fund’s investments in fixed-income securities. When interest rates rise, the value of existing investments in fixed-income securities tends to fall and this decrease in value may not be offset by higher income from new investments. Interest-rate risk is generally greater for fixed-income securities with longer maturities or durations.

Inflation Risk: This is the risk that the value of assets or income from investments will be less in the future as inflation decreases the value of money. As inflation increases, the value of the Fund’s assets can decline as can the value of the Fund’s distributions. This risk is significantly greater for fixed-income securities with longer maturities.

Foreign (Non-US) Risk: Investments in securities of non-US issuers may involve more risk than those of US issuers. These securities may fluctuate more widely in price and may be more difficult to trade due to adverse market, economic, political, regulatory or other factors.

Currency Risk: Fluctuations in currency exchange rates may negatively affect the value of the Fund’s investments or reduce its returns.

Emerging-Market Risk: Investments in emerging-market countries may have more risk because the markets are less developed and less liquid as well as being subject to increased economic, political, regulatory or other uncertainties.

Alternative Investments Risk: Many alternative investments can be volatile and may be illiquid. Their performance may have little correlation with the performance of equity or fixed-income markets, and they may not perform in accordance with expectations.

Capitalization Risk: Investments in small- and mid-capitalization companies may be more volatile than investments in large-capitalization companies. Investments in small-capitalization companies may have additional risks because these companies have limited product lines, markets or financial resources.

DISCLOSURES AND RISKS (continued)

Derivatives Risk: Derivatives may be difficult to price or unwind and leveraged so that small changes may produce disproportionate losses for the Fund. Derivatives, especially over-the-counter derivatives, are also subject to counterparty risk.

Leverage Risk: To the extent the Fund uses leveraging techniques, its NAV may be more volatile because leverage tends to exaggerate the effect of changes in interest rates and any increase or decrease in the value of the Fund’s investments.

Commodity Risk: Investing in commodities and commodity-linked derivative instruments may subject the Fund to greater volatility than investments in traditional securities. The value of commodity-linked derivative instruments may be affected by overall market movements, commodity index volatility, changes in interest rates, or factors affecting a particular industry or commodity, such as drought, floods, weather, livestock disease, embargoes, tariffs and international economic, political and regulatory developments.

Subsidiary Risk: By investing in the Subsidiary, the Fund is indirectly exposed to the risks associated with the Subsidiary. The derivatives and other investments held by the Subsidiary are generally similar to those that are permitted to be held by the Fund and are subject to the same risks that apply to similar investments if held directly by the Fund. The Subsidiary is not registered under the Investment Company Act of 1940, as amended (the “1940 Act”), and, unless otherwise noted in the prospectus, is not subject to all of the investor protections of the 1940 Act. However, the Fund wholly owns and controls the Subsidiary, and the Fund and the Subsidiary are managed by the Adviser, making it unlikely the Subsidiary will take actions contrary to the interests of the Fund or its shareholders. In addition, changes in federal tax laws applicable to the Fund or interpretations thereof could limit the Fund’s ability to gain exposure to commodities investments through investments in the Subsidiary.

Short Sale Risk: The Fund is subject to short sale risk because it may engage in short sales either directly or indirectly through investment in the Underlying Portfolio. Short sales involve the risk that the Fund or Underlying Portfolio will incur a loss by subsequently buying a security at a higher price than the price at which it sold the security. The amount of such loss is theoretically unlimited, as it will be based on the increase in value of the security sold short. In contrast, the risk of loss from a long position is limited to the Fund’s or Underlying Portfolio’s investment in the security, because the price of the security cannot fall below zero. The Fund or Underlying Portfolio may not always be able to close out a short position on favorable terms.

DISCLOSURES AND RISKS (continued)

Management Risk: The Fund is subject to management risk because it is an actively managed investment fund. The Adviser will apply its investment techniques and risk analyses in making investment decisions for the Fund, but there is no guarantee that its techniques will produce the intended results.

These risks are fully discussed in the Fund’s prospectus. As with all investments, you may lose money by investing in the Fund.

An Important Note About Historical Performance

The investment return and principal value of an investment in the Fund will fluctuate as the prices of the individual securities in which it invests fluctuate, so that your shares, when redeemed, may be worth more or less than their original cost. Performance shown in this report represents past performance and does not guarantee future results. Current performance may be lower or higher than the performance information shown. You may obtain performance information current to the most recent month-end by visiting www.abfunds.com. The performance shown for periods prior to April 24, 2017 is based on the Fund’s prior principal strategies and may not be representative of the Fund’s performance under its current principal strategies. Class B shares are no longer being offered. Effective November 7, 2019, all outstanding Class B shares were converted to Class A shares. Please see Note A for more information.

All fees and expenses related to the operation of the Fund have been deducted. NAV returns do not reflect sales charges; if sales charges were reflected, the Fund’s quoted performance would be lower. SEC returns reflect the applicable sales charges for each share class: a 4.25% maximum front-end sales charge for Class A shares and a 1% 1-year contingent deferred sales charge for Class C shares. Returns for the different share classes will vary due to different expenses associated with each class. Performance assumes reinvestment of distributions and does not account for taxes.

HISTORICAL PERFORMANCE

GROWTH OF A $10,000 INVESTMENT IN THE FUND (unaudited)

8/31/2010 TO 8/31/2020

This chart illustrates the total value of an assumed $10,000 investment in AB All Market Total Return Portfolio Class A shares (from 8/31/2010 to 8/31/2020) as compared to the performance of the Fund’s benchmarks. The chart reflects the deduction of the maximum 4.25% sales charge from the initial $10,000 investment in the Fund and assumes the reinvestment of dividends and capital gains distributions.

The Fund’s current prospectus fee table shows the Fund’s total annual operating expense ratios as 1.10%, 1.85%, 0.85%, 1.51%, 1.20% and 0.87% for Class A, Class C, Advisor Class, Class R, Class K and Class I shares, respectively. The Financial Highlights section of this report sets forth expense ratio data for the current reporting period; the expense ratios shown above may differ from the expense ratios in the Financial Highlights section since they are based on different time periods.

EXPENSE EXAMPLE

(unaudited)

As a shareholder of the Fund, you incur two types of costs: (1) transaction costs, including sales charges (loads) on purchase payments, contingent deferred sales charges on redemptions and (2) ongoing costs, including management fees; distribution (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 as indicated below.

Actual Expenses

The table below provides information about actual account values and actual expenses. You may use the information, 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 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 table below also provides information about hypothetical account values and hypothetical expenses based on the Fund’s actual expense ratio and an assumed annual rate of return of 5% 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 by comparing this 5% hypothetical example with the 5% hypothetical examples that appear in the shareholder reports of 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), or contingent deferred sales charges on redemptions. Therefore, the hypothetical example 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.

PORTFOLIO SUMMARY

August 31, 2020 (unaudited)

PORTFOLIO STATISTICS

Net Assets ($mil): $639.6

PORTFOLIO SUMMARY (continued)

August 31, 2020 (unaudited)

CONSOLIDATED PORTFOLIO OF INVESTMENTS

August 31, 2020