Summary Prospectus by Investment Company (Form 497K)

Portfolio Turnover. The Fund pays 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. For the fiscal year ended July 31, 2025, the Fund's portfolio turnover rate was 113% of the average value of its portfolio.

Principal Investment Strategies

The Fund seeks to achieve its investment objective by investing, under normal circumstances, at least 80% of its net assets, plus the amount of any borrowings for investment purposes, in municipal securities issued in the State of California (the "State" or "California") by or on behalf of California state or local governments or agencies, whose interest payments are exempt from regular U.S. federal and California state income taxes. The Fund's

investments in derivatives will be counted toward the Fund's 80% policy to the extent that they provide investment exposure to the securities included within that policy or to one or more market risk factors associated with such securities.

Under normal circumstances, the Fund will primarily invest in U.S. dollar-denominated investment-grade short-term fixed- and floating-rate municipal securities issued by California with remaining maturities of five years or less, such as municipal bonds, municipal notes and variable rate demand obligations, as well as money market instruments and registered investment companies. Investment-grade securities are rated BBB- or higher by S&P Global Ratings and/or Fitch Ratings, Inc. ("Fitch"), or Baa3 or higher by Moody's Investors Service, Inc. ("Moody's"), or, if unrated, determined by the Fund's management team to be of equivalent quality. Municipal bonds include debt obligations issued by or on behalf of a governmental entity or other qualifying issuer that pay interest that is, in the opinion of bond counsel to the issuer at the time of issuance, generally

excludable from gross income for U.S. federal and California state income tax purposes.

The Fund may invest up to 20% of its net assets in securities that are not California municipal bonds (including, but not limited to, taxable municipal bonds, U.S. Treasury and Government agency issues, and investment grade corporate bonds). Further, the Fund may invest up to 20% of its net assets in municipal securities that pay interest that is subject to the federal alternative minimum tax. Issuers of such securities may be states, territories and possessions of the U.S., including the District of Columbia, and their political subdivisions, agencies and instrumentalities.

BFA or its affiliates may advise the money market funds and investment companies in which the Fund may invest.

Under normal circumstances, the effective duration of the Fund's portfolio is expected to be 1.5 years or less, as calculated by the Fund's management team. Effective duration is a measure of the Fund's price sensitivity to changes in yields or interest rates; however, investors should be aware that effective duration is not an exact measurement and may not reliably predict a particular security's price sensitivity to changes in yield or interest rates.

Under normal circumstances, the Fund will also seek to maintain a weighted average maturity that is less than three years. Weighted average maturity is a U.S. dollar-weighted average of the remaining term to maturity of the underlying securities in the Fund's portfolio. Maturity of a debt security

refers to the date upon which debt securities are due to be repaid, that is, the date when the issuer generally must pay back the face amount of the security.

The Fund is an actively managed exchange-traded fund ("ETF") that does not seek to track the performance of a specified index. The Fund may have a higher degree of portfolio turnover than funds that seek to track the performance of an index.

The Fund is classified as non-diversified under the Investment Company Act of 1940, as amended (the "1940 Act").

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 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.

Municipal Securities Risks. Municipal securities risks include the ability of the issuer to repay the obligation, the relative lack of information about certain issuers of municipal securities, and the possibility of future legislative changes which could affect the market for and value of municipal securities. Budgetary constraints of local, state,

and federal governments upon which the issuers may be relying for funding may also impact municipal securities. These risks include:

General Obligation Bonds Risks. Timely payments depend on the issuer's credit quality, ability to raise tax revenues and ability to maintain an adequate tax base.

Revenue Bonds Risks. These payments depend on the money earned by the particular facility or class of facilities, or the amount of revenues derived from another source.

Private Activity Bonds Risks. Municipalities and other public authorities issue private activity bonds to finance development of industrial facilities for use by a private enterprise. The private enterprise pays the principal and interest on the bond, and the issuer does not pledge its full faith, credit and taxing power for repayment.

Moral Obligation Bonds Risks. Moral obligation bonds are generally issued by special purpose public authorities of a state or municipality. If the issuer is unable to meet its obligations, repayment of these bonds becomes a moral commitment, but not a legal obligation, of the state or municipality.

Municipal Notes Risks. Municipal notes are shorter term municipal debt obligations. If there is a shortfall in the anticipated proceeds, the notes may not be fully repaid and the Fund may lose money.

Municipal Lease Obligations Risks. In a municipal lease obligation, the issuer agrees to make payments when due on the lease obligation. Although the issuer does not pledge its unlimited taxing power for payment of the lease

obligation, the lease obligation is secured by the leased property.

Tax-Exempt Status Risk. The Fund and its investment manager will rely on the opinion of issuers' bond counsel and, in the case of derivative securities, sponsors' counsel, on the tax-exempt status of interest on municipal bonds and payments under derivative securities. Neither the Fund nor its investment manager will independently review the bases for those tax opinions, which may ultimately be determined to be incorrect and subject the Fund and its shareholders to substantial tax liabilities.

State Specific Risk. Because the Fund invests primarily in California municipal securities, it is more exposed to adverse political, economic and regulatory developments within the state than a fund that invests more widely.

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.

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.

Assets Under Management (AUM) Risk. From time to time, an Authorized Participant (as defined in the Creations and Redemptions section of the Fund's 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 may effect some or 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.

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.

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 dispose of illiquid investments during periods when shareholders are redeeming or selling

their shares or the Fund's net assets otherwise shrink, the Fund will need to dispose of 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 greater 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 or sales of Fund shares 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. During periods of market volatility, liquidity in the market for the Fund's shares may be impacted by the liquidity in the market for the underlying securities or instruments held by the Fund, which could lead to the Fund's shares trading at a premium or discount to the Fund's NAV.

Issuer Risk. Fund performance depends on the performance of individual securities to which the Fund has exposure. Changes in the financial condition or credit rating of an issuer of

those securities may cause the value of the securities to decline.

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 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.

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.

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 significantly less than the underlying value of the Fund shares.

Non-Diversification Risk. The Fund is a non-diversified fund. Because the Fund may invest in securities of a smaller number of issuers, it may be more exposed to the risks associated with and developments affecting an individual issuer than a fund that invests more widely.

Operational and Technology Risks. The Fund is directly and indirectly susceptible to operational and technology risks, including those related to human errors, processing errors, communication errors, systems failures, cybersecurity incidents, and the use of artificial intelligence and machine learning ("AI"), which may result in losses for the Fund and its shareholders or may impair the Fund's operations. While the Fund's service providers are required to have appropriate operational, information security and cybersecurity risk management policies and procedures, their methods of risk management may differ from those of the Fund. Operational and technology risks for the issuers in which the Fund invests

could also result in material adverse consequences for such issuers and may cause the Fund's investments in such issuers to lose value.

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.

School District Investment Risk. School districts rely, in part, on funding appropriations from, among others, the federal government and state governments. As a result, municipal securities issued by school districts may be adversely affected by political and economic changes at the state or federal levels, such as decreased tax or other revenues, spending reductions or changes in appropriations. Municipal securities that are issued to finance a particular school district project often depend on revenues from ad valorem taxes (i.e., property taxes) to make principal and interest payments. Adverse conditions and developments affecting a particular project can result in lower revenues to the issuer of the municipal securities. Investors in these securities, similar to investors in municipal securities generally, face heightened risk of loss upon insolvency of the school district issuers because there is often no ready source of funding to pay the bonds other than the local tax base, which a bankruptcy court or administrator does not control.

Taxability Risk. Future laws, regulations, rulings or court decisions may cause interest on municipal securities to be subject, directly or indirectly, to U.S. federal income taxation or currently exempt interest on

state municipal securities to be subject to state or local income taxation, or the value of state municipal securities that are currently exempt to be subject to state or local intangible personal property tax, or may otherwise prevent the Fund from realizing the full current benefit of the tax-exempt status of such securities. Any such change could also affect the market price of such securities, and thus the value of an investment in the Fund.

Legal Opinion Risk. The Fund will rely on legal opinions of counsel to issuers of municipal securities as to the tax-exempt status of investments and will not do its own analysis. The status of a municipal security as tax-exempt may be affected by events that occur after the municipal security is issued.

Valuation Risk. The price that the Fund could receive upon the sale (or other disposition) of a security or other asset may differ from the Fund's valuation of the security or other asset, particularly for securities or other assets that trade in low volume or volatile markets or that are valued using a fair value methodology. In addition, the value of the securities or other assets in the Fund's portfolio may change on days or during time periods when investors are not able to purchase or sell Fund shares.

Authorized Participants that create or redeem Fund shares on days when the Fund is holding fair-valued securities or other assets may receive fewer or more shares, or lower or higher redemption proceeds, than they would have received had the securities or other assets not been fair valued or been valued using a different methodology. The ability to value investments may be impacted by technological issues or

errors by pricing services or other third-party service providers.

Variable and Floating Rate Instrument Risk. Variable and floating rate securities provide for periodic adjustment in the interest rate paid on the securities. Securities with floating or variable interest rates can be less sensitive to interest rate changes than securities with fixed interest rates, but may decline in value if their coupon rates do not reset as high, or as quickly, as comparable market interest rates, and generally carry lower yields than fixed securities of the same maturity. These securities will not generally increase in value if interest rates decline. A decline in interest rates may result in a reduction in income received from variable and floating rate securities held by the

Fund and may adversely affect the value of the Fund's shares. These securities may be subject to greater illiquidity risk than other fixed income securities, meaning the absence of an active market for these securities could make it difficult for the Fund to dispose of them at any given time. Floating rate securities generally are subject to legal or contractual restrictions on resale, may trade infrequently, and their value may be impaired when the Fund needs to liquidate such loans. Benchmark interest rates may not accurately track market interest rates. Although floating rate securities are less sensitive to interest rate risk than fixed-rate securities, they are subject to credit risk and default risk, which could impair their value.

Management

Investment Adviser. BlackRock Fund Advisors.

Portfolio Managers. Kristi Manidis, Christian Romaglino, CFA and Alicia De Lorenzo (the "Portfolio Managers") are jointly and primarily responsible for the day-to-day management of the Fund. Ms. Manidis, Mr. Romaglino and Ms. De Lorenzo have been Portfolio Managers of the Fund since 2023, 2023 and 2024, 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 primarily from net tax-exempt income (but not necessarily free from federal AMT), although distributions of taxable capital gains may also occur. The Fund is generally not an appropriate investment for a 401(k) plan or an individual retirement account ("IRA"). Please consult your personal tax advisor.

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.