Summary Prospectus by Investment Company (Form 497K)

SUMMARY PROSPECTUS January 31, 2025,

as revised November 7, 2025

Maximum Sales Charge (Load) Imposed on Purchases

(as a percentage of offering price)

Maximum Deferred Sales Charge (Load)

(as a percentage of offering price or redemption proceeds, whichever is lower)

Management Fees

Fee Waiver(a)

Net Management Fees

Distribution and/or Service (12b-1) Fees

Other Expenses:

Transfer Agent

Other Expenses

Total Other Expenses

Total Annual Portfolio Operating Expenses

Fee Waiver and/or Expense Reimbursement(b)

Total Annual Portfolio Operating Expenses After Fee Waiver and/or Expense Reimbursement

Effective November 7, 2025, the Manager has contractually agreed to waive 0.15% of its management fee from the Portfolio until January 31, 2027. This waiver agreement may be terminated or changed only with the consent of the Board of Directors.

Restated to reflect new expense limitations, which became effective on November 7, 2025. The Manager has contractually agreed to waive its management fee and/or to bear certain expenses of the Portfolio to the extent necessary to prevent total Portfolio operating expenses (excluding any acquired fund fees and expenses other than the advisory fees of any AB Funds in which the Portfolio may invest, interest expense, taxes, extraordinary expenses, and brokerage commissions, and other transaction costs), on an annualized basis, from exceeding 0.28% of average daily net assets for Class Z shares. The agreement will remain in effect until January 31, 2027 and may only be terminated or changed with the consent of the Portfolio's Board of Directors. In addition, the agreement will be automatically extended for one-year terms unless the Manager provides notice of termination to the Portfolio at least 60 days prior to the end of the period.

After 1 Year

After 3 Years

After 5 Years

Interest Rate Risk: Changes in interest rates will affect the value of 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. Changing interest rates may have unpredictable effects on the markets, may result in heightened market volatility and may detract from Portfolio performance. In addition, changes in monetary policy may exacerbate the risks associated with changing interest rates.

Credit Risk: This is the risk that the issuer or the guarantor of a debt security, or the counterparty to a derivatives or other contract, will be unable or unwilling to make timely principal and/or interest payments, or to otherwise honor its obligations. The issuer or guarantor may default, potentially 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, although credit ratings are opinions and not guarantees of quality. 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 tend to have a higher probability that an issuer will default or fail to meet its payment obligations, making credit risk greater for medium-quality and lower-rated debt securities. Lower-rated debt securities and similar unrated securities (commonly known as "junk bonds") have speculative elements or are predominantly speculative credit risks. At times when credit risk is perceived to be greater, credit "spreads" (i.e., the difference between the yields on lower quality securities and the yields on higher quality securities) may get larger or "widen". As a result, the values of the lower quality securities may go down more and they may become harder to sell.

Duration Risk: The duration of a fixed-income security may be shorter than or equal to full maturity of the fixed-income security. Fixed-income securities with longer durations have more interest rate risk and will decrease in price as interest rates rise. Securities that have final maturities longer than their durations may be affected by increased credit spreads to a far greater degree than their durations would suggest, because they are exposed to credit risk until final maturity.

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 Portfolio's assets can decline as can the value of the Portfolio's distributions. This risk is significantly greater for fixed-income securities with longer maturities.

Inflation-Protected Securities Risk: The terms of inflation-protected securities provide for the coupon and/or maturity value to be adjusted based on changes in an inflation index. Decreases in the inflation rate or in investors' expectations about inflation could cause these securities to underperform non-inflation-adjusted securities on a total-return basis. In addition, there can be no assurance that the relevant inflation index will accurately measure the rate of inflation, in which case the securities may not work as intended. These securities may be more difficult to trade or dispose of than other types of securities.

Foreign (Non-U.S.) Securities Risk: Investments in foreign securities entail significant risks in addition to those customarily associated with investing in U.S. securities, such as less liquid, less transparent, less regulated and more volatile markets. These risks include risks related to unfavorable or unsuccessful government actions, reduction of government or central bank support, economic sanctions and tariffs and potential responses to those sanctions and tariffs, inadequate accounting standards and auditing and financial recordkeeping requirements, lack of information, social instability, armed conflict, and other adverse market, economic, political and regulatory factors, all of which could disrupt the financial markets in which the Portfolio invests and adversely affect the value of the Portfolio's assets.

Emerging Markets Securities Risk: The risks of investing in foreign (non-U.S.) securities are heightened with respect to issuers in emerging-market countries because the markets are less developed, less liquid and subject to increased potential for market manipulation, and there may be a greater amount of economic, political and social uncertainty. These risks are even more pronounced in "frontier" markets, which are investable markets with lower total market capitalization and liquidity than the more developed emerging markets. Emerging markets typically have fewer medical and economic resources than more developed countries, and thus they may be less able to control or mitigate the effects of a pandemic, climate change, or a natural disaster.

Derivatives Risk: The Portfolio may use derivatives as direct investments to earn income, enhance return and broaden portfolio diversification, which entail greater risk than if used solely for hedging purposes. While hedging can guard against potential risks, there is also a risk that a derivative intended as a hedge may not perform as expected. In addition to other risks such as the credit risk of the counterparty (the party on the other side of the transaction), derivatives involve the risk that changes in the value of the derivative may not correlate with relevant assets, rates or indices. Derivatives may be difficult to price or unwind, and small changes may produce disproportionate losses for the Portfolio. Certain derivatives have the potential for unlimited loss, regardless of the size of the initial investment. Assets required to be set aside or posted as margin or collateral for derivatives positions may themselves go down in value, and these collateral and other requirements may limit investment flexibility. Some derivatives involve leverage, which can make the Portfolio more volatile and can compound other risks. Derivatives, especially

over-the-counter derivatives, are also subject to counterparty risk, which is the risk that the counterparty on a derivative transaction will be unable or unwilling to honor its contractual obligations to the Portfolio. Use of derivatives may have different tax consequences for the Portfolio than an investment in the underlying asset or index, and such differences may affect the amount, timing and character of income distributed to shareholders. The U.S. Government and certain foreign governments have adopted regulations governing derivatives markets, including mandatory clearing of certain derivatives as well as additional regulations governing margin, reporting and registration requirements. The ultimate impact of the regulations remains unclear. Additional regulation may make derivatives more costly, limit their availability or utility, otherwise adversely affect their performance, or disrupt markets.

Mortgage-Related and Asset-Related Securities Risk: Mortgage- and asset-related securities represent interests in "pools" of mortgages or other assets, including consumer loans or receivables held in trust. Mortgage- and asset-related securities are subject to credit, interest rate, prepayment and extension risks. These securities also are subject to risk of default on the underlying mortgage or asset, particularly during periods of economic downturn. Small movements in interest rates (both increases and decreases) may quickly and significantly reduce the value of certain mortgage-related securities. Asset-related securities entail certain risks not presented by mortgage-backed securities, including the risk that it may be difficult to perfect the liens securing any collateral backing certain asset-backed securities.

Prepayment and Extension Risk: Prepayment risk is the risk that a loan, bond or other security might be called or otherwise converted, prepaid or redeemed before maturity. If this happens, particularly during a time of declining interest rates or credit spreads, the Portfolio will not benefit from the rise in market price that normally accompanies a decline in interest rates, and may not be able to invest the proceeds in securities providing as much income, resulting in a lower yield to the Portfolio. Conversely, extension risk is the risk that as interest rates rise or spreads widen, payments of securities may occur more slowly than anticipated by the market. If this happens, the values of these securities may go down because their interest rates are lower than current market rates and they remain outstanding longer than anticipated.

Subordination Risk: The Portfolio may invest in securities that are subordinated to more senior securities of an issuer, or which represent interests in pools of such subordinated securities. Subordinated securities will be disproportionately affected by a default or even a perceived decline in creditworthiness of the issuer. Subordinated securities are more likely to suffer a credit loss than non-subordinated securities of the same issuer, any loss incurred by the subordinated securities is likely to be proportionately greater, and any recovery of interest or principal may take more time.

Illiquid Investments Risk: Illiquid investments risk exists when particular investments are difficult or impossible to purchase or sell, possibly preventing the Portfolio from purchasing or selling these securities at an advantageous price. In certain cases, governmental actions could prevent sales of securities or repatriation of proceeds. Over recent years, regulatory changes have led to reduced liquidity in the marketplace, and the capacity of dealers to make markets in fixed-income securities has been outpaced by the growth in the size of the fixed-income markets. Illiquid investments risk may be magnified in a rising interest rate environment, where the value and liquidity of fixed-income securities generally go down. Illiquid securities may also be difficult to value. If the Portfolio is forced to sell an illiquid asset to meet redemption requests or other cash needs, or to try to limit losses, the Portfolio may be forced to sell at a substantial loss or may not be able to sell at all.

Redemption Risk: The Portfolio may experience heavy redemptions that could cause the Portfolio to liquidate its assets at inopportune times or unfavorable prices or increase or accelerate taxable gains or transaction costs and may negatively affect the Portfolio's net asset value ("NAV"), or performance, which could cause the value of your investment to decline. Redemption risk is heightened during periods of overall market turmoil.

Foreign Currency Risk: This is the risk that changes in foreign (non-U.S.) currency exchange rates may negatively affect the value of the Portfolio's investments or reduce the returns of the Portfolio. For example, the value of the Portfolio's investments in foreign securities and foreign currency positions may decrease if the U.S. Dollar is strong (i.e., gaining value relative to other currencies) and other currencies are weak (i.e., losing value relative to the U.S. Dollar).

Actions by a Few Major Investors: In certain countries, volatility may be heightened by actions of a few major investors. For example, substantial increases or decreases in cash flows of mutual funds investing in these markets could significantly affect local securities prices and, therefore, share prices of the Portfolio.

Market Risk: The Portfolio is subject to market risk, which is the risk that securities prices in general or in particular countries or sectors may decline over short or extended periods. Securities prices may decline in response to adverse changes in the economy or the economic outlook; deterioration in investor sentiment; interest rate, currency and commodity price fluctuations; inflationary pressures; adverse geopolitical, social or environmental developments; issuer- and sector-specific considerations; public health crises (including the occurrence of a contagious disease or illness) and regional and global conflicts (including war or civil disturbance and acts of terrorism); cybersecurity events; market disruptions caused by the imposition of new or additional tariffs, or changing interest rate levels; trade disputes; levels of government debt and deficits and measures to address budget deficits; downgrading of sovereign debt; sanctions or other government actions; and other factors.

Lower-rated Securities Risk: Lower-rated securities, or junk bonds/high-yield securities, are subject to greater risk of loss of principal and interest and greater market risk than higher-rated securities. The capacity of issuers of lower-rated securities to pay interest and repay principal is more likely to weaken than is that of issuers of higher-rated securities in times of deteriorating economic conditions or rising interest rates.

Active Trading Risk: The Portfolio expects to engage in active and frequent trading of its portfolio securities and its portfolio turnover rate may greatly exceed 100%. A higher rate of portfolio turnover increases transaction costs, which may negatively affect the Portfolio's return. In addition, a high rate of portfolio turnover may result in substantial short-term gains, which may have adverse tax consequences for Portfolio shareholders.

Management Risk: The Portfolio is subject to management risk because it is an actively-managed investment portfolio. The Manager will apply its investment techniques and risk analyses in making investment decisions for the Portfolio, but these techniques, analyses and decisions may not work as intended or may not produce the desired results, and may, during certain periods, result in increased volatility for the Portfolio or cause the value of the Portfolio's shares to go down. In some cases, derivatives and other investment techniques may be unavailable, or the Manager may determine not to use them, possibly even under market conditions where their use could benefit the Portfolio. Some of these techniques may incorporate, or rely upon, quantitative models,

but there is no guarantee that these models will generate accurate forecasts, reduce risk or otherwise perform as expected. In addition, the Manager may change the Portfolio's investment strategies or policies from time to time. Those changes may not lead to the results intended by the Manager and could have an adverse effect on the value or performance of the Portfolio.

how the Portfolio's performance changed from year to year over ten years; and

how the Portfolio's average annual returns for one, five and ten years compare to those of a broad-based securities market index.

Bloomberg U.S. Aggregate Bond Index

(reflects no deduction for fees, expenses, or taxes)

Inception date of Class Z shares: July 23, 2019. Performance information for periods prior to the inception of Class Z shares is the performance of the Portfolio's Core Bond Class shares, adjusted to reflect the net expense differences between the Core Bond Class and Class Z shares.

Investors who qualify for Class Z shares as institutional clients of the Manager must have at least $2,000,000 invested in the Portfolio.