Summary Prospectus by Investment Company (Form 497K)

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iShares Russell 2000 Small-Cap Index Fund

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The fees and expenses shown in the table and the example that follows include both the expenses of Russell 2000 Small-Cap Index Fund and Russell 2000 Small-Cap Index Fund's share of the allocated expenses of Master Small Cap Index Series (the "Series"), a series of Quantitative Master Series LLC (the "Master LLC"). The management fees are paid by the Series.

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As described in the "Management of the Funds" section of the Fund's prospectus beginning on page 38, BlackRock has contractually agreed to waive the management fee with respect to any portion of the Series' assets estimated to be attributable to investments in other equity and fixed-income mutual funds and exchange-traded funds managed by BlackRock or its affiliates that have a contractual management fee, through June 30, 2027. In addition, BlackRock has contractually agreed to waive its management fees by the amount of investment advisory fees the Series pays to BlackRock indirectly through its investment in money market funds managed by BlackRock or its affiliates, through June 30, 2027. The contractual agreements may be terminated upon 90 days' notice by a majority of the non-interested directors of the Master LLC or by a vote of a majority of the outstanding voting securities of the Series.

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As described in the "Management of the Funds" section of the Fund's prospectus beginning on page 38, BlackRock has contractually agreed to waive and/or reimburse fees and/or expenses in order to limit Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements of Russell 2000 Small-Cap Index Fund (excluding Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses) to 0.37% for Investor P Shares of average daily net assets through June 30, 2027. In addition to the contractual waiver with respect to the Fund, BlackRock has contractually agreed to waive and/or reimburse fees or expenses in order to limit Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements of the Series (excluding Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Series expenses) to 0.07% of average daily net assets through June 30, 2027. These contractual agreements may be terminated upon 90 days' notice by a majority of the non-interested directors of the Corporation or of the Master LLC, as applicable, or by a vote of a majority of the outstanding voting securities of the Fund or the Series, as applicable.

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Small Cap Securities Risk - Small cap companies may have limited product lines or markets. They may be less financially secure than larger, more established companies. They may depend on a more limited management group than larger capitalized companies.

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Index-Related Risk - The index provider may rely on various sources of information to assess the criteria of components of the Underlying Index, including information that may be based on assumptions and estimates. Neither the Fund nor BlackRock can offer assurances that the index provider's methodology or sources of information will provide an accurate assessment of included components. Errors in index data, index computations or the construction of the Underlying Index in accordance with its methodology may occur, and the index provider may not identify or correct them promptly or at all, which may have an adverse impact on the Fund and its shareholders. Unusual market conditions or other unforeseen circumstances (such as natural disasters, political

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Passive Investment Risk - Because BlackRock does not select individual companies in the index that the Fund tracks, the Fund may hold securities of companies that present risks that an investment adviser researching individual securities might seek to avoid.

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Tracking Error Risk - The Fund is subject to the risk of "tracking error," which is the divergence of the Fund's performance from that of the Underlying Index. Tracking error may occur due to a number of factors, including differences between the securities and other assets held in the Fund's portfolio and those included in the Underlying Index; differences in the timing and methodologies used to value securities and other assets; transaction costs and other expenses incurred by the Fund that the Underlying Index does not incur; the Fund's holding of uninvested cash; differences in the timing of the accrual or the valuation of dividends or interest received by the Fund or distributions paid to Fund shareholders; tax gains or losses; differences between the amount and/or timing of withholding taxes on dividends reflected in the Underlying Index from the Fund's obligation, if any, for foreign withholding taxes; the requirements for the Fund to maintain pass-through tax treatment; portfolio transactions carried out to minimize the distribution of capital gains to shareholders; changes to the Underlying Index, such as during a rebalancing or reconstitution; and impacts to the Fund of complying with certain regulatory requirements or limits. A fund that tracks an index composed of a large number of securities or other assets may experience greater tracking error than a fund that tracks a more narrow index. Tracking error risk may be heightened during times of increased market volatility or other unusual market conditions.

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Equity Securities Risk - Stock markets are volatile. The price of equity securities fluctuates based on changes in a company's financial condition and overall market and economic conditions.

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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.

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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.

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Representative Sampling Risk - Representative sampling is a method of indexing that involves investing in a representative sample of securities that collectively have a similar investment profile to the Underlying Index and resemble the Underlying Index in terms of risk factors and other key characteristics. The Fund may or may not hold every security in the Underlying Index. When the Fund deviates from a full replication indexing strategy to utilize a representative sampling strategy, the Fund is subject to an increased risk of tracking error, in that the securities selected in the aggregate for the Fund may not have an investment profile similar to those of the Underlying Index.

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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.