# EDGAR Filing Document

**Accession Number:** 0001804196
**File Stem:** 0001193125-25-167687
**Filing Date:** 2025-7
**Character Count:** 39121
**Document Hash:** 641fe21dbc4d1652615fd1f6a48ac590
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-25-167687.hdr.sgml**: 20250729

**ACCESSION NUMBER**: 0001193125-25-167687

**CONFORMED SUBMISSION TYPE**: 497K

**PUBLIC DOCUMENT COUNT**: 4

**FILED AS OF DATE**: 20250729

**DATE AS OF CHANGE**: 20250729

**EFFECTIVENESS DATE**: 20250729

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** BlackRock ETF Trust II
- **CENTRAL INDEX KEY:** 0001804196

**ORGANIZATION NAME:**
- **EIN:** 000000000
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 0731

**FILING VALUES:**
- **FORM TYPE:** 497K
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-236575
- **FILM NUMBER:** 251159586

**BUSINESS ADDRESS:**
- **STREET 1:** 100 BELLEVUE PARKWAY
- **CITY:** WILMINGTON
- **STATE:** DE
- **ZIP:** 19809
- **BUSINESS PHONE:** 800 882 0052

**MAIL ADDRESS:**
- **STREET 1:** 100 BELLEVUE PARKWAY
- **CITY:** WILMINGTON
- **STATE:** DE
- **ZIP:** 19809

## Series and Classes Contracts Data

### iShares Mortgage-Backed Securities Active ETF (Series ID: S000093898)

| Class ID   | Class Name                                    | Ticker Symbol   |
|:---|:---|:---|
| C000262359 | iShares Mortgage-Backed Securities Active ETF |  |

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| | |
|:---|:---|
|  ![LOGO](g44930g56p99.jpg)  | **JULY 23, 2025** |

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**2025 Summary Prospectus** 

**BlackRock ETF Trust II** 

● **iShares Mortgage-Backed Securities Active ETF \| MBBA \| CBOE BZX** 

*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 (including amendments and supplements), reports to shareholders and other information about the Fund, including the Fund's statement of additional information, online at https://www.blackrock.com/prospectus. You can also get this information at no cost by calling 1-800-474-2737 or by sending an e-mail request to prospectus.request@blackrock.com, or from your financial professional. The Fund's prospectus and statement of additional information, both dated July 23, 2025, as amended and supplemented from time to time, are incorporated by reference into (legally made a part of) this Summary Prospectus.* 

*The Securities and Exchange Commission has not approved or disapproved these securities or passed upon the adequacy of this Summary Prospectus. Any representation to the contrary is a criminal offense.* 

&nbsp;&nbsp;&nbsp;**Not FDIC Insured • May Lose Value • No Bank Guarantee**

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iSHARES MORTGAGE-BACKED SECURITIES ACTIVE ETF

Ticker: MBBA Stock Exchange: CBOE BZX

**Investment Objective** 

The investment objective of iShares Mortgage-Backed Securities Active ETF (the "Fund") is to seek to maximize total return, consistent with income generation and prudent investment management.

**Fees and Expenses** 

The following table describes the fees and expenses that you will incur if you buy, hold and sell shares of the Fund. The investment advisory agreement between BlackRock ETF Trust II (the "Trust") and BlackRock Fund Advisors ("BFA") (the "Investment Advisory Agreement") provides that BFA will pay all operating expenses of the Fund, except: (i) the management fees, (ii) interest expenses, (iii) taxes, (iv) expenses incurred with respect to the acquisition and disposition of portfolio securities and the execution of portfolio transactions, including brokerage commissions, (v) distribution fees or expenses, and (vi) litigation expenses and any extraordinary expenses. The Fund may incur "Acquired Fund Fees and Expenses." Acquired Fund Fees and Expenses reflect the Fund's pro rata share of the fees and expenses incurred indirectly by the Fund as a result of investing in other investment companies. The impact of Acquired Fund Fees and Expenses is included in the total returns of the Fund.

You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and Example below.

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| | | | | | |
|:---|:---|:---|:---|:---|:---|
| **Annual Fund Operating Expenses<br>(ongoing expenses that you pay each year as a<br>percentage of the value of your investments)** | **Annual Fund Operating Expenses<br>(ongoing expenses that you pay each year as a<br>percentage of the value of your investments)** | **Annual Fund Operating Expenses<br>(ongoing expenses that you pay each year as a<br>percentage of the value of your investments)** | **Annual Fund Operating Expenses<br>(ongoing expenses that you pay each year as a<br>percentage of the value of your investments)** | **Annual Fund Operating Expenses<br>(ongoing expenses that you pay each year as a<br>percentage of the value of your investments)** | **Annual Fund Operating Expenses<br>(ongoing expenses that you pay each year as a<br>percentage of the value of your investments)** |
| **Management<br>Fees** | **Distribution and<br>Service (12b-1)<br>Fees** | **Other<br>Expenses<sup>1</sup>** | **Total Annual<br>Fund<br>Operating<br>Expenses** | **Fee<br>Waiver<sup>2</sup>** | **Total Annual<br>Fund<br>Operating<br>Expenses<br>After Fee Waiver<sup>1</sup>** |
| 0.25% |  | 0.00% | 0.25% | (0.00)% | 0.25% |

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<sup>1</sup> Other Expenses are based on estimated amounts for the Fund's current fiscal year. 

<sup>2</sup> As described in the "Management" section of the Fund's prospectus beginning on page 21, BFA has contractually agreed to waive a portion of its management fees in an amount equal to the aggregate Acquired Fund Fees and Expenses, if any, attributable to investments by the Fund in other equity and fixed-income mutual funds and exchange-traded funds ("ETFs") advised by BFA or its affiliates through June 30, 2027. As described in the "Management" section of the Fund's prospectus beginning on page 21, BFA has contractually agreed to waive a portion of its management fees in an amount equal to the aggregate Acquired Fund 

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Fees and Expenses, if any, attributable to investments by the Fund in money market funds managed by BFA or its affiliates through June 30, 2027. The agreement (with respect to either waiver)may be terminated upon 90 days' notice by a majority of the non-interested trustees of the Trust or by a vote of a majority of the outstanding voting securities of the Fund. <br>

**Example.** This Example is intended to help you compare the cost of owning shares of the Fund with the cost of investing in other funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then sell all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions, your costs would be:

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| | |
|:---|:---|
| **1 Year** | **3 Years** |
| $26 | $80 |

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**Portfolio Turnover**. The Fund may pay 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 and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in the Annual Fund Operating Expenses or in the Example, affect the Fund's performance. There has been no portfolio turnover because the Fund has not commenced operations as of the date of this prospectus (the "Prospectus"), but it is expected that BlackRock Mortgage-Backed Securities Fund, a series of BlackRock Funds V (the "Predecessor Fund"), will be reorganized into the Fund. During the Predecessor Fund's fiscal year ended September 30, 2024, the portfolio turnover rate was 1,338% of the average value of its portfolio.

**Principal Investment Strategies**. Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in mortgage-backed securities ("MBS") and derivatives that provide investment exposure to such

securities or to one or more market risk factors associated with such securities. Such securities include, but are not limited to, securities issued by Government National Mortgage Association ("GNMA"), Federal National Mortgage Association ("Fannie Mae") and Federal Home Loan Mortgage Corporation ("Freddie Mac") as well as other U.S. Government securities.

The Fund may participate in to be announced ("TBA") transactions. A TBA transaction is a method of trading MBS where the buyer and seller agree upon general trade parameters such as agency, settlement date, par amount and price at the time the contract is entered into but the MBS are delivered in the future, generally 30 days later. The actual pools of MBS delivered in a TBA transaction typically are not determined until two days prior to settlement date.

The Fund measures its performance against the Bloomberg U.S. MBS Index (the "Benchmark"). Under normal circumstances, the Fund seeks to maintain an average portfolio duration that is within ±1 year of the duration of the Benchmark.

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The Fund makes investments in residential and commercial MBS as well as other asset backed securities.

The Fund may buy or sell options or futures on a security or an index of securities, or enter into credit default swaps and interest rate transactions, including swaps (collectively, commonly known as derivatives). The Fund may seek to obtain market exposure to the securities in which it primarily invests by entering into a series of purchase and sale contracts or by using other investment techniques (such as reverse repurchase agreements or dollar rolls).

The Fund typically uses derivatives as a substitute for taking a position in the underlying asset and/or as part of a strategy designed to reduce exposure to other risks, such as interest rate risk. From time to time, the Fund will use derivatives to enhance returns, in which case their use would involve leveraging risk.

**Summary of Principal Risks** 

As with any investment, you could lose all or part of your investment in the Fund, and the Fund's performance could trail that of other investments. The Fund is subject to certain risks, including the principal risks noted below, any of which may adversely affect the Fund's net asset value per share ("NAV"), trading price, yield, total return and ability to meet its investment objective. Unlike many exchange-traded funds ("ETFs"), the Fund is not an index-based ETF. Certain key risks are prioritized below (with others following in alphabetical order), but the relative significance of any risk is difficult to predict and may change over time. You should review each risk factor carefully.

***Mortgage- and Asset-Backed Securities Risks.*** Mortgage- and asset-backed securities represent interests in "pools" of mortgages or other assets, including consumer loans or receivables held in trust. Mortgage- and asset-backed 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-backed securities.

***Debt Securities Risk*.** Debt securities, such as bonds, involve risks, such as credit risk, interest rate risk, extension risk, and prepayment risk, each of which are described in further detail below:

*Credit Risk* — Credit risk refers to the possibility that the issuer of a debt security (i.e., the borrower) will not be able to make payments of interest and principal when due. Changes in an issuer's credit rating or the market's perception of an issuer's creditworthiness may also affect the value of the Fund's investment in that issuer. The degree of credit risk depends on both the financial condition of the issuer and the terms of the obligation.

*Interest Rate Risk* — The market value of bonds and other fixed-income securities changes in response to interest rate changes and other factors. Interest rate risk is the risk that prices of bonds and other fixed-income securities will increase as interest rates fall and decrease as interest rates rise.

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The Fund may be subject to a greater risk of rising interest rates during a period of historically low interest rates. For example, if interest rates increase by 1%, assuming a current portfolio duration of ten years, and all other factors being equal, the value of the Fund's investments would be expected to decrease by 10%. (Duration is a measure of the price sensitivity of a debt security or portfolio of debt securities to relative changes in interest rates.) The magnitude of these fluctuations in the market price of bonds and other fixed-income securities is generally greater for those securities with longer maturities. Fluctuations in the market price of the Fund's investments will not affect interest income derived from instruments already owned by the Fund, but will be reflected in the Fund's net asset value. The Fund may lose money if short-term or long-term interest rates rise sharply in a manner not anticipated by Fund management.

To the extent the Fund invests in debt securities that may be prepaid at the option of the obligor (such as mortgage-backed securities), the sensitivity of such securities to changes in interest rates may increase (to the detriment of the Fund) when interest rates rise. Moreover, because rates on certain floating rate debt securities typically reset only periodically, changes in prevailing interest rates (and particularly sudden and significant changes) can be expected to cause some fluctuations in the net asset value of the Fund to the extent that it invests in floating rate debt securities.

These basic principles of bond prices also apply to U.S. Government securities. A security backed by the

"full faith and credit" of the U.S. Government is guaranteed only as to its stated interest rate and face value at maturity, not its current market price. Just like other fixed-income securities, government-guaranteed securities will fluctuate in value when interest rates change.

A general rise in interest rates has the potential to cause investors to move out of fixed-income securities on a large scale, which may increase redemptions from funds that hold large amounts of fixed-income securities. Heavy redemptions could cause the Fund to sell assets at inopportune times or at a loss or depressed value and could hurt the Fund's performance.

*Extension Risk* — When interest rates rise, certain obligations will be paid off by the obligor more slowly than anticipated, causing the value of these obligations to fall.

*Prepayment Risk* — When interest rates fall, certain obligations will be paid off by the obligor more quickly than originally anticipated, and the Fund may have to invest the proceeds in securities with lower yields.

***U.S. Government Issuer Risk.*** Treasury obligations may differ in their interest rates, maturities, times of issuance and other characteristics. Obligations of U.S. Government agencies and authorities are supported by varying degrees of credit but generally are not backed by the full faith and credit of the U.S. Government. No assurance can be given that the U.S. Government will provide financial support to its agencies and authorities if it is not obligated by law to do so.

***Assets Under Management (AUM) Risk*.** From time to time, an Authorized

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Participant (as defined in the Creations and Redemptions section of this prospectus), a third-party investor, the Fund's adviser, an affiliate of the Fund's adviser, or another fund may invest in the Fund and hold its investment for a specific period of time to allow the Fund to achieve size or scale. There can be no assurance that any such entity would not redeem its investment or that the size of the Fund would be maintained at such levels, which could negatively impact the Fund.

***Authorized Participant Concentration Risk*.** Only an Authorized Participant may engage in creation or redemption transactions directly with the Fund. There are a limited number of institutions that may act as Authorized Participants for the Fund, including on an agency basis on behalf of other market participants. No Authorized Participant is obligated to engage in creation or redemption transactions. To the extent that Authorized Participants exit the business or do not place creation or redemption orders for the Fund and no other Authorized Participant places orders, Fund shares are more likely to trade at a premium or discount to NAV and possibly face trading halts or delisting.

***Cash Transactions Risk.*** The Fund expects to effect all of its creations and redemptions for cash, rather than in-kind securities. As a result, the Fund may have to sell portfolio securities at inopportune times in order to obtain the cash needed to meet redemption orders. This may cause the Fund to sell a security and recognize a capital gain or loss that might not have been incurred if it had made a redemption in-kind. The use of cash creations and redemptions may also cause the Fund's

shares to trade in the market at wider bid-ask spreads or greater premiums or discounts to the Fund's NAV.

***Derivatives Risk.*** The Fund's use of derivatives may increase its costs, reduce the Fund's returns and/or increase volatility. Derivatives involve significant risks, including:

*Leverage Risk* — The Fund's use of derivatives can magnify the Fund's gains and losses. Relatively small market movements may result in large changes in the value of a derivatives position and can result in losses that greatly exceed the amount originally invested.

*Market Risk* — Some derivatives are more sensitive to interest rate changes and market price fluctuations than other securities. The Fund could also suffer losses related to its derivatives positions as a result of unanticipated market movements, which losses are potentially unlimited. Finally, BFA may not be able to predict correctly the direction of securities prices, interest rates and other economic factors, which could cause the Fund's derivatives positions to lose value.

*Counterparty Risk* — Derivatives are also subject to counterparty risk, which is the risk that the other party in the transaction will be unable or unwilling to fulfill its contractual obligation, and the related risks of having concentrated exposure to such a counterparty.

*Illiquidity Risk* — The possible lack of a liquid secondary market for derivatives and the resulting inability of the Fund to sell or otherwise close a derivatives position could expose the Fund to losses and could make derivatives more difficult for the Fund to value accurately.

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*Operational Risk* — The use of derivatives includes the risk of potential operational issues, including documentation issues, settlement issues, systems failures, inadequate controls and human error.

*Legal Risk* — The risk of insufficient documentation, insufficient capacity or authority of counterparty, or legality or enforceability of a contract.

*Volatility and Correlation Risk* — Volatility is defined as the characteristic of a security, an index or a market to fluctuate significantly in price within a short time period. A risk of the Fund's use of derivatives is that the fluctuations in their values may not correlate with the overall securities markets.

*Valuation Risk* — Valuation for derivatives may not be readily available in the market. Valuation may be more difficult in times of market turmoil since many investors and market makers may be reluctant to purchase complex instruments or quote prices for them.

*Hedging Risk* — Hedges are sometimes subject to imperfect matching between the derivative and the underlying security, and there can be no assurance that the Fund's hedging transactions will be effective. The use of hedging may result in certain adverse tax consequences.

*Tax Risk* — Certain aspects of the tax treatment of derivative instruments, including swap agreements and commodity-linked derivative instruments, are currently unclear and may be affected by changes in legislation, regulations or other legally binding authority. Such treatment may be less favorable than that given to a direct investment in an underlying asset

and may adversely affect the timing, character and amount of income the Fund realizes from its investments.

***Dollar Rolls Risk.*** Dollar rolls involve the risk that the market value of the securities that the Fund is committed to buy may decline below the price of the securities the Fund has sold. These transactions may involve leverage.

***High Portfolio Turnover Risk*.** The Fund may engage in active and frequent trading of its portfolio securities. High portfolio turnover (more than 100%) may result in increased transaction costs to the Fund, including brokerage commissions, dealer mark ups and other transaction costs on the sale of the securities and on reinvestment in other securities. The sale of Fund portfolio securities may result in the realization and/or distribution to shareholders of higher capital gains or losses as compared to a fund with less active trading policies, such as index ETFs. These effects of higher than normal portfolio turnover may adversely affect Fund performance.

***Large Shareholder and Large-Scale Redemption Risk.*** Certain shareholders, including an Authorized Participant, a third-party investor, the Fund's adviser or an affiliate of the Fund's adviser, a market maker, or another entity, may from time to time own or manage a substantial amount of Fund shares, or may invest in the Fund and hold their investment for a limited period of time. There can be no assurance that any large shareholder or large group of shareholders would not redeem their investment.

Redemptions of a large number of Fund shares could require the Fund to dispose of assets to meet the

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redemption requests, which can accelerate the realization of taxable income and/or capital gains and cause the Fund to make taxable distributions to its shareholders earlier than the Fund otherwise would have. In addition, under certain circumstances, non-redeeming shareholders may be treated as receiving a disproportionately large taxable distribution during or with respect to such year. In some circumstances, the Fund may hold a relatively large proportion of its assets in cash in anticipation of large redemptions, diluting its investment returns. These large redemptions may also force the Fund to sell portfolio securities when it might not otherwise do so, which may negatively impact the Fund's NAV, increase the Fund's brokerage costs and/or have a material effect on the market price of the Fund shares.

***Illiquid Investments Risk.*** The Fund may not acquire any illiquid investment if, immediately after the acquisition, the Fund would have invested more than 15% of its net assets in illiquid investments. An illiquid investment is any investment that the Fund reasonably expects cannot be sold or disposed of in current market conditions in seven calendar days or less without the sale or disposition significantly changing the market value of the investment. Liquid investments may become illiquid after purchase by the Fund, particularly during periods of market turmoil. There can be no assurance that a security or instrument that is deemed to be liquid when purchased will continue to be liquid for as long as it is held by the Fund, and any security or instrument held by the Fund may be deemed an illiquid investment pursuant to the Fund's

liquidity risk management program. The Fund's illiquid investments may reduce the returns of the Fund because it may be difficult to sell the illiquid investments at an advantageous time or price. In addition, if the Fund is limited in its ability to sell illiquid investments during periods when shareholders are redeeming their shares, the Fund will need to sell liquid securities to meet redemption requests and illiquid securities will become a larger portion of the Fund's holdings. An investment may be illiquid due to, among other things, the reduced number and capacity of traditional market participants to make a market in fixed-income securities or the lack of an active trading market. To the extent that the Fund's principal investment strategies involve derivatives or securities with substantial market and/or credit risk, the Fund will tend to have the greatest exposure to the risks associated with illiquid investments. Illiquid investments may be harder to value, especially in changing markets, and if the Fund is forced to sell these investments to meet redemption requests or for other cash needs, the Fund may suffer a loss. This may be magnified in a rising interest rate environment or other circumstances where investor redemptions from fixed-income mutual funds may be higher than normal. In addition, when there is illiquidity in the market for certain securities, the Fund, due to limitations on illiquid investments, may be subject to purchase and sale restrictions.

***Leverage Risk*.** Some transactions may give rise to a form of economic leverage. These transactions may include, among others, derivatives, and may expose the Fund to greater risk and increase its costs. The use of

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leverage may cause the Fund to liquidate portfolio positions when it may not be advantageous to do so to satisfy its obligations or to meet the applicable requirements of the Investment Company Act and the rules thereunder. Increases and decreases in the value of the Fund's portfolio will be magnified when the Fund uses leverage.

***Management Risk.*** The Fund is subject to management risk, which is the risk that the investment process, techniques and analyses applied by BFA or a sub-adviser will not produce the desired results, and those securities or other financial instruments selected by BFA or a sub-adviser may result in returns that are inconsistent with the Fund's investment objective. In addition, legislative, regulatory, or tax developments may affect the investment techniques available to BFA or a sub-adviser in connection with managing the Fund and may also adversely affect the ability of the Fund to achieve its investment objective.

***Market Risk and Selection Risk*.** Market risk is the risk that one or more markets in which the Fund invests will go down in value, including the possibility that the markets will go down sharply and unpredictably. The value of a security or other asset may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security or other asset, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Local, regional or global events such as war, acts of terrorism, the spread of infectious illness or other public health issues like pandemics or

epidemics, recessions, or other events could have a significant impact on the Fund and its investments. Selection risk is the risk that the securities selected by Fund management will underperform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. This means you may lose money.

Recent policy initiatives undertaken by the U.S. government have the potential to impact international relations, trade agreements and the overall regulatory environment in ways that could create uncertainty and instability in domestic and global markets, and could adversely affect the investment performance of the Fund. In particular, actions taken by the U.S. government in respect of international trade relations could lead to trade wars, increased costs for imported goods, disruptions in supply chains, reduced foreign investment, and instability in regions where the Fund invests.

***Market Trading Risk*.** The Fund faces numerous market trading risks, including the potential lack of an active market for Fund shares (including through a trading halt), losses from trading in secondary markets, periods of high volatility, and disruptions in the process of creating and redeeming Fund shares. Any of these factors, among others, may lead to the Fund's shares trading in the secondary market at a premium or discount to NAV or to the intraday value of the Fund's portfolio holdings. If you buy Fund shares at a time when the market price is at a premium to NAV or sell Fund shares at a time when the market price is at a discount to NAV, you may pay significantly more or receive

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significantly less than the underlying value of the Fund shares.

***Repurchase Agreements and Purchase and Sale Contracts Risk.*** If the other party to a repurchase agreement or purchase and sale contract defaults on its obligation under the agreement, the Fund may suffer delays and incur costs or lose money in exercising its rights under the agreement. If the seller fails to repurchase the security in either situation and the market value of the security declines, the Fund may lose money.

***Reverse Repurchase Agreements Risk.*** Reverse repurchase agreements involve the sale of securities held by the Fund with an agreement to repurchase the securities at an agreed-upon price, date and interest payment. Reverse repurchase agreements involve the risk that the other party may fail to return the securities in a timely manner or at all. The Fund could lose money if it is unable to recover the securities and the value of the collateral held by the Fund, including the value of the investments made with cash collateral, is less than the value of the securities. These events could also trigger adverse tax consequences for the Fund. In addition, reverse repurchase agreements involve the risk that the interest income earned in the investment of the proceeds will be less than the interest expense.

***Risk of Investing in the United States*.** Certain changes in the U.S.

economy, such as when the U.S. economy weakens or when its financial markets decline, may have an adverse effect on the securities to which the Fund has exposure.

***Small Fund Risk***. When the Fund's size is small, the Fund may experience low trading volume and wide bid/ask spreads. The Fund's performance near its inception date may not represent how the Fund will perform in the future or with a larger asset base. The Fund may buy smaller-sized bonds known as "odd lots," which may be purchased or sold at a discount to similar "round lot" bonds. The prices used by the Fund may differ from the value that would be realized if these securities were sold, and the impact of such pricing differences on the Fund's performance may be heightened when the Fund's size is small. In addition, the Fund may face the risk of being delisted if it does not meet certain requirements set by the listing exchange. Any resulting liquidation of the Fund could lead to elevated transaction costs for the Fund and negative tax consequences for its shareholders.

**Performance Information** 

The Fund has not commenced operations as of the date of this prospectus. The returns presented for the Fund reflect the performance of the Predecessor Fund. It is anticipated that on or about January 23, 2026, the Fund will adopt the performance of the

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Predecessor Fund as a result of a reorganization in which the Fund will acquire all of the assets and assume certain stated liabilities of the Predecessor Fund (the "Reorganization"). Performance shown below is based on the investment objective and investment strategies utilized by the Predecessor Fund, which are the same as those of the Fund. The Predecessor Fund is a mutual fund that is managed by a different investment adviser that is under common control with BFA and has the same portfolio management team as that of the Fund. The returns presented for the Fund reflect the performance of Institutional Shares of the Predecessor Fund.

The bar chart and table that follow show how the Predecessor Fund has performed on a calendar year basis and provide an indication of the risks of investing in the Predecessor Fund by showing how the Predecessor Fund's average annual returns for 1, 5, and 10 years compare with that of the Bloomberg U.S. Aggregate Bond Index and the Bloomberg U.S. MBS Index. The Predecessor Fund acquired all of the assets, subject to the liabilities, of BlackRock GNMA Portfolio, a series of BlackRock Funds II, as a result of a different reorganization on September 17, 2018. The performance information of the Predecessor Fund below is based on the performance of the

BlackRock GNMA Portfolio for periods prior to the date of such reorganization. The BlackRock GNMA Portfolio had the same investment objective, strategies and policies, portfolio management team and contractual arrangements, including the same contractual fees and expenses, as the Predecessor Fund as of the date of such reorganization. The Predecessor Fund's and the BlackRock GNMA Portfolio's total returns prior to January 28, 2025 as reflected in the bar chart and table are the returns of the Predecessor Fund and the BlackRock GNMA Portfolio, as applicable, when each followed a different investment objective and different investment strategies and process under the name "BlackRock GNMA Portfolio." Effective January 28, 2025, the Predecessor Fund changed the benchmark against which it measures its performance from the Bloomberg GNMA Total Return Index Value Unhedged USD to the Bloomberg U.S. Aggregate Bond Index and the Bloomberg U.S. MBS Index. Fund management believes the Bloomberg U.S. MBS Index more accurately reflects the investment strategy of the Fund. Both assume that all dividends and distributions have been reinvested in the Predecessor Fund. Past performance (before and after taxes) does not necessarily indicate how the Predecessor Fund will perform in the future.

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Fund's returns would have been lower. Updated information on the Fund's performance, including its current net asset value, can be obtained by visiting www.blackrock.com or can be obtained by phone at (800) 882-0052.

**Investor A Shares** 

**ANNUAL TOTAL RETURNS** 

**BlackRock Mortgage-Backed Securities Fund** 

**As of 12/31**![LOGO](g44930g00a06.jpg)

During the ten-year period shown in the bar chart, the highest return for a quarter was 7.27% (quarter ended December 31, 2023) and the lowest return for a quarter was -5.60% (quarter ended September 30, 2022).

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| | | | |
|:---|:---|:---|:---|
| **Average Annual Total Returns**<br> **For the periods ended 12/31/24** | **Average Annual Total Returns**<br> **For the periods ended 12/31/24** | **Average Annual Total Returns**<br> **For the periods ended 12/31/24** | **Average Annual Total Returns**<br> **For the periods ended 12/31/24** |
|  | **1 Year** | **5 Years** | **10 Years** |
|  **BlackRock Mortgage-Backed Securities Fund — Investor A Shares** |  |  |  |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Return Before Taxes | (3.10)% | (1.88)% | (0.03)% |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Return After Taxes on Distributions | (4.50)% | (2.96)% | (1.18)% |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Return After Taxes on Distributions and Sale of Fund Shares | (1.84)% | (1.85)% | (0.50)% |
|  **BlackRock Mortgage-Backed Securities Fund — Investor C Shares** |  |  |  |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Return Before Taxes | (0.68)% | (1.81)% | (0.22)% |
|  **BlackRock Mortgage-Backed Securities Fund — Institutional Shares** |  |  |  |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Return Before Taxes | 1.30% | (0.82)% | 0.66% |
|  **Bloomberg U.S. Aggregate Bond Index<sup>1</sup>** (Reflects no deduction for fees, expenses or taxes) | 1.25% | (0.33)% | 1.35% |
|  **Bloomberg U.S. MBS Index<sup>2</sup>** (Reflects no deduction for fees, expenses or taxes) | 1.20% | (0.74)% | 0.91% |
|  **Bloomberg GNMA Total Return Index Value Unhedged USD<sup>3</sup>** (Reflects no deduction for fees, expenses or taxes) | 0.96% | (0.60)% | 0.85% |

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<sup>1</sup> The Fund has added this broad-based index in response to new regulatory requirements.

<sup>2</sup> The Fund has added this additional benchmark.

<sup>3</sup> Effective approximately one year from the date of the Fund's prospectus, the Fund will no longer compare its performance to this index.

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**Management** 

**Investment Adviser.** The Fund's investment adviser is BlackRock Fund Advisors.

**Portfolio Managers.** Matthew Kraeger, Daniel Someck, Nicholas Kramvis and Siddharth Mehta (the "Portfolio Managers") are jointly and primarily responsible for the day to day management of the Fund. Including the management of the Predecessor Fund, Messrs. Kraeger, Someck, Kramvis and Mehta have been Portfolio Managers of the Fund since 2009, 2025, 2025 and 2017, respectively.

**Purchase and Sale of Fund Shares** 

The Fund is an ETF. Individual shares of the Fund may only be bought and sold in the secondary market through a broker-dealer. Because ETF shares trade at market prices rather than at NAV, shares may trade at a price greater than NAV (a premium) or less than NAV (a discount). An investor may incur costs attributable to the difference between the highest price a buyer is willing to pay to purchase shares of the Fund (bid) and the lowest price a seller is willing to accept for shares of the Fund (ask) when buying or selling shares in the secondary market (the "bid ask spread").

**Tax Information** 

The Fund intends to make distributions that may be taxable to you as ordinary income or capital gains, unless you are investing through a tax-deferred arrangement such as a 401(k) plan or an individual retirement account ("IRA"), in which case, your distributions generally will be taxed when withdrawn.

**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), BFA or other related companies may pay the intermediary for marketing activities and presentations, educational training programs, conferences, the development of technology platforms and reporting systems or other services related to the sale or promotion of the Fund. These payments may create a conflict of interest by influencing the broker-dealer or other 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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**For more information visit www.blackrock.com or call 1-800-474-2737** 

Investment Company Act File # 811-23511

SPRO-MBBA-0725

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