SUMMARY PROSPECTUS    January 31, 2022

AB Short Duration Income Portfolio

Ticker: Class A–SHUAX; Class C–SHUCX; Advisor Class–SHUYX

Before you invest, you may want to review the Fund’s Prospectus, which contains more information about the Fund and its risks. The Fund’s Prospectus and Statement of Additional Information (“SAI”), both dated January 31, 2022, as may be amended or supplemented, are incorporated by reference into this Summary Prospectus. For free paper or electronic copies of the Fund’s Prospectus, reports to shareholders and other information about the Fund, go to www.abfunds.com/go/prospectus, email a request to prorequest@alliancebernstein.com, call (800) 227-4618, or ask any financial advisor, bank, or broker-dealer who offers shares of the Fund. The Fund’s reports to shareholders are also available at www.abfunds.com/go/SDI.

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INVESTMENT OBJECTIVE

The Fund’s investment objective is to seek high current income consistent with preservation of capital.

FEES AND EXPENSES OF THE FUND

This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund. You may be required to pay commissions and/or other forms of compensation to a broker for transactions in Advisor Class shares, which are not reflected in the tables or the examples below. You may qualify for sales charge reductions if you and members of your family invest, or agree to invest in the future, at least $100,000 in AB Mutual Funds. More information about these and other discounts is available from your financial intermediary and in Investing in the Funds—Sales Charge Reduction Programs for Class A Shares on page 65 of the Fund’s Prospectus, in Appendix C—Financial Intermediary Waivers of the Fund’s Prospectus and in Purchase of Shares—Sales Charge Reduction Programs for Class A Shares on page 134 of the Fund’s SAI.

Shareholder Fees (fees paid directly from your investment)

	Class A Shares (prior to 3/7/22)	Class A Shares (effective on 3/7/22)	Class C Shares	Advisor Class Shares
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	4.25%(a)	2.25%(a)	None	None
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower)	None(b)	None(c)	1.00%(d)	None
Exchange Fee	None	None	None	None

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

	Class A		Class C		Advisor Class
Management Fees		.35%		.35%		.35%
Distribution and/or Service (12b-1) Fees		.20%		1.00%		None
Other Expenses:
Transfer Agent		.08%		.07%		.07%
Interest Expense		.03%		.02%		.02%
Other Expenses		.60%		.75%		.74%
Total Other Expenses		.71%		.84%		.83%
Total Annual Fund Operating Expenses		1.26%		2.19%		1.18%
Fee Waiver and/or Expense Reimbursement(e)		(.58)%		(.72)%		(.71)%
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement(f)		.68%		1.47%		.47%

(a) Effective on March 7, 2022, the maximum sales charge for purchases of Class A shares is reduced from 4.25% to 2.25%.

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(b) Prior to March 7, 2022, purchases of Class A shares in amounts of $1,000,000 or more, or by certain group retirement plans, may be subject to a 1%, 1-year contingent deferred sales charge, or CDSC, which may be subject to waiver in certain circumstances.

(c) Effective on March 7, 2022, purchases of Class A shares in amounts of $500,000 or more, or by certain group retirement plans, may be subject to a 1%, 18-month CDSC, which may be subject to waiver in certain circumstances.

(d) For Class C shares, the CDSC is 0% after the first year. Class C shares automatically convert to Class A shares after eight years.

(e) The Adviser has contractually agreed to waive its management fees and/or to bear expenses of the Fund until January 31, 2023 to the extent necessary to prevent total Fund operating expenses (excluding acquired fund fees and expenses other than the advisory fees of any AB Mutual Funds in which the Fund may invest, interest expense, taxes, extraordinary expenses, and brokerage commissions and other transaction costs), on an annualized basis, from exceeding .65%, 1.45% and .45% of average daily net assets, respectively, for Class A, Class C and Advisor Class shares (“expense limitations”). Any fees waived and expenses borne by the Adviser may be reimbursed by the Fund until the end of the third fiscal year after the fiscal period in which the fee was waived or the expense was borne, provided that no reimbursement payment will be made that would cause the Fund’s covered operating expenses to exceed the applicable expense limitations. The agreement will remain in effect until January 31, 2023 and may only be terminated or changed with the consent of the Fund’s Board of Directors. In addition, the agreement will be automatically extended for one-year terms unless the Adviser provides notice of termination to the Fund at least 60 days prior to the end of the period.

(f) If interest expense were excluded, net expenses would be as follows:

Class A		Class C		Advisor Class
	.65%		1.45%		.45%

Examples

The Examples are intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Examples assume that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Examples also assume that your investment has a 5% return each year, that the Fund’s operating expenses stay the same and that any fee waiver and/or expense limitation is in effect for only the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	Class A* (effective prior to 3/7/22)		Class A** (effective on 3/7/22)		Class C			Advisor Class
After 1 Year	$	492	$	293	$	250	***	$	48
After 3 Years	$	753	$	560	$	616		$	304
After 5 Years	$	1,034	$	847	$	1,109		$	580
After 10 Years	$	1,834	$	1,663	$	2,230		$	1,369

* This Example reflects amounts that would be paid by investors in Class A shares who pay a maximum sales charge of 4.25% (in effect prior to March 7, 2022).

** This Example reflects amounts that would be paid by investors in Class A shares who pay a maximum sales charge of 2.25% (in effect beginning on March 7, 2022).

*** If you did not redeem your shares at the end of the period, your expenses would be decreased by approximately $100.

Portfolio Turnover

The Fund pays transaction costs, such as commissions, when it buys or 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 the Annual Fund Operating Expenses or in the Examples, affect the Fund’s performance. During the most recent fiscal period, the Fund’s portfolio turnover rate was 163% of the average value of its portfolio.

PRINCIPAL STRATEGIES

The Fund pursues its objective by investing, under normal circumstances, primarily in income-producing securities. The Fund also normally invests at least 65% of its total assets in securities of U.S. and foreign governments and their agencies and instrumentalities (including mortgage-backed securities), derivatives related to such securities, and repurchase agreements relating to U.S. Government securities. Under normal circumstances, the Fund will maintain a dollar-weighted average duration of less than three years, although it may invest in securities of any duration or maturity.

The Fund may invest in non-government fixed-income securities, including corporate debt securities, non-government mortgage-backed and other asset-backed securities, certificates of deposit and commercial paper. The Fund may invest up to 35% of its net assets in below investment grade securities (commonly known as “junk bonds”). The Fund’s investments in foreign securities may include both government and corporate securities, and securities of emerging market countries or of issuers in emerging markets.

The Adviser selects securities for purchase or sale based on its assessment of the securities’ risks and return characteristics as well as the securities’ impact on the overall risks and return characteristics of the Fund. In making this assessment, the Adviser takes into account various factors, including the credit quality and sensitivity to interest rates of the securities under consideration and of the Fund’s other holdings.

The Fund may utilize derivatives, such as options, futures contracts, forwards and swaps. The Fund may, for example, use interest rate futures contracts and swaps to establish exposure to the fixed-income markets or particular fixed-income securities. Derivatives may provide a more efficient and economical exposure to market segments than direct investments, and may also be a more efficient way to alter the Fund’s exposure. The Fund may also enter into transactions such as reverse repurchase agreements that are

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similar to borrowings for investment purposes. The Fund’s use of derivatives and these borrowing transactions may create aggregate exposure that is substantially in excess of its net assets, effectively leveraging the Fund.

The Adviser may hedge the foreign currency exposure resulting from the Fund’s security positions, and may take long or short positions in currencies, through the use of currency-related derivatives.

PRINCIPAL RISKS

• Market Risk: The value of the Fund’s assets will fluctuate as the bond market fluctuates. 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.

• 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.

• Below Investment Grade Securities Risk: 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. These securities may be subject to greater price volatility due to such factors as specific corporate developments and negative perceptions of the junk bond market generally and may be more difficult to trade than other types of securities.

• 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. The current historically low interest rate environment heightens the risks associated with rising interest rates.

• Duration Risk: Duration is a measure that relates the expected price volatility of a fixed-income security to changes in interest rates. The duration of a fixed-income security may be shorter than or equal to the full maturity of a fixed-income security. Fixed-income securities with longer durations have more risk and will decrease in price as interest rates rise.

• 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.

• Mortgage-Related and/or Other Asset-Backed Securities Risk: Investments in mortgage-related and other asset-backed securities are subject to certain additional risks. The value of these securities may be particularly sensitive to changes in interest rates. These risks include “extension risk”, which is the risk that, in periods of rising interest rates, issuers may delay the payment of principal, and “prepayment risk”, which is the risk that in periods of falling interest rates, issuers may pay principal sooner than expected, exposing the Fund to a lower rate of return upon reinvestment of principal. Mortgage-backed securities offered by non-governmental issuers and other asset-backed securities may be subject to other risks, such as higher rates of default in the mortgages or assets backing the securities or risks associated with the nature and servicing of mortgages or assets backing the securities.

• Foreign (Non-U.S.) Risk: Investments in securities of non-U.S. issuers may involve more risk than those of U.S. 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.

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

• 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, which is the risk that the counterparty (the party on the other side of the transaction) on a derivative transaction will be unable or unwilling to honor its contractual obligations to the Fund.

• Leverage Risk: To the extent the Fund uses leveraging techniques, its net asset value, or 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.

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

• Illiquid Investments Risk: Illiquid investments risk exists when certain investments become difficult to purchase or sell. Difficulty in selling such investments may result in sales at disadvantageous prices affecting the value of your investment in the Fund. Causes of illiquid investments risk may include low trading volumes, large positions and heavy redemptions of Fund shares.

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Illiquid investments risk may be higher in a rising interest rate environment, when the value and liquidity of fixed-income securities generally decline.

• Active Trading Risk: The Fund 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 Fund’s return. In addition, a high rate of portfolio turnover may result in substantial short-term gains, which may have adverse tax consequences for Fund shareholders.

• 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, but there is no guarantee that its techniques will produce the intended results. 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.

As with all investments, you may lose money by investing in the Fund.

BAR CHART AND PERFORMANCE INFORMATION

The bar chart and performance information provide an indication of the historical risk of an investment in the Fund by showing:

• how the Fund’s performance changed from year to year over the life of the Fund; and

• how the Fund’s average annual returns for one year and since inception compare to those of a broad-based securities market index.

You may obtain updated performance information on the website at www.abfunds.com (click on “Investments—Mutual Funds”).

The Fund’s past performance before and after taxes, of course, does not necessarily indicate how it will perform in the future.

Bar Chart

The annual returns in the bar chart are for the Fund’s Class A shares and do not reflect sales loads. If sales loads were reflected, returns would be less than those shown.

During the period shown in the bar chart, the Fund’s:

Best Quarter was up 4.48%, 2nd quarter, 2020; and Worst Quarter was up -6.84%, 1st quarter, 2020.

Performance Table

Average Annual Total Returns

(For the periods ended December 31, 2021)

		1 Year		Since Inception*
Class A** (maximum sales charge of 4.25%)	Return Before Taxes		-4.22%		2.03%
	Return After Taxes on Distributions		-5.63%		0.33%
	Return After Taxes on Distributions and Sale of Fund Shares		-2.42%		0.85%
Class A**, *** (maximum sales charge of 2.25%)	Return Before Taxes		-2.19%		2.72%
	Return After Taxes on Distributions		-3.63%		1.00%
	Return After Taxes on Distributions and Sale of Fund Shares		-1.22%		1.36%
Class C	Return Before Taxes		-1.83%		2.64%
Advisor Class	Return Before Taxes		0.23%		3.64%
Bloomberg 1-5 Year U.S. Government/Credit Index (reflects no deduction for fees, expenses, or taxes)			-0.97%		3.10%

* Inception date for all Classes is 12/12/18.

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** After-tax returns:

– Are shown for Class A shares only and will vary for the other Classes of shares because these Classes have different expense ratios;

– Are an estimate, which is based on the highest historical individual federal marginal income tax rates, and do not reflect the impact of state and local taxes; actual after-tax returns depend on an individual investor’s tax situation and are likely to differ from those shown; and

– Are not relevant to investors who hold Fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.

Effective on March 7, 2022, the maximum sales charge for purchases of Class A shares is reduced from 4.25% to 2.25%.

*** The returns for Class A shares for the periods shown have been adjusted to reflect a maximum sales charge of 2.25% (reduced from 4.25% effective on March 7, 2022).

INVESTMENT ADVISER

AllianceBernstein L.P. is the investment adviser for the Fund.

PORTFOLIO MANAGERS

The following table lists the persons responsible for day-to-day management of the Fund’s portfolio:

Employee	Length of Service	Title
Scott A. DiMaggio	Since 2018	Senior Vice President of the Adviser
Gershon M. Distenfeld	Since 2018	Senior Vice President of the Adviser
Fahd Malik	Since January 2022	Senior Vice President of the Adviser
Matthew S. Sheridan	Since 2018	Senior Vice President of the Adviser

PURCHASE AND SALE OF FUND SHARES

Purchase Minimums

The following table describes the initial and subsequent minimum purchase amounts for each class of shares, which are subject to waiver in certain circumstances.

	Initial	Subsequent
Class A/Class C shares, including traditional IRAs and Roth IRAs	$2,500	$50
Automatic Investment Program	None	$50 If initial minimum investment is less than $2,500, then $200 monthly until account balance reaches $2,500
Advisor Class shares (only available to fee-based programs or through other limited arrangements and certain commission-based brokerage arrangements)	None	None
Class A shares are available at NAV, without an initial sales charge, to 401(k) plans, 457 plans, employer-sponsored 403(b) plans, profit-sharing and money purchase pension plans, defined benefit plans, and non-qualified deferred compensation plans, where in each case plan level or omnibus accounts are held on the books of the Fund.	None	None

You may sell (redeem) your shares each day the New York Stock Exchange is open. You may sell your shares through your financial intermediary or by mail (AllianceBernstein Investor Services, Inc., P.O. Box 786003, San Antonio, TX 78278-6003) or telephone (800) 221-5672.

TAX INFORMATION

The Fund may pay income dividends or make capital gains distributions, which may be subject to federal income taxes and taxable as ordinary income or capital gains, and may also be subject to state and local taxes.

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 or a group retirement plan), the Fund and its related companies may pay the intermediary for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other financial intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary’s website for more information.

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