UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED MANAGEMENT

INVESTMENT COMPANIES

Investment Company Act file number: 811-07899 and 811-07885

Name and address of agent for service: John M. Perlowski, Chief Executive Officer, BlackRock Index Funds, Inc. and Quantitative Master Series LLC, 55 East 52^nd Street, New York, NY 10055

Registrants’ telephone number, including area code: (800) 441-7762

Date of fiscal year end: 12/31/2022

Date of reporting period: 06/30/2022

(a) The Report to Shareholders is attached herewith.

BlackRock Funds^SM

·  iShares Municipal Bond Index Fund

·  iShares Short-Term TIPS Bond Index Fund

BlackRock Index Funds, Inc.

·  iShares MSCI EAFE International Index Fund

·  iShares Russell 2000 Small-Cap Index Fund

Table of Contents

Investment Objective

iShares Municipal Bond Index Fund’s (the “Fund”) investment objective is to seek to provide investment results that correspond to the total return performance of fixed-income securities in the aggregate, as represented by the ICE BofA US Municipal Securities Index (the “Underlying Index”).

Portfolio Management Commentary

How did the Fund perform?

For the six-month period ended June 30, 2022, the Fund’s Institutional Shares returned (8.93)%, Investor A shares returned (9.05)%, Class K Shares returned (8.91)%, and Investor P Shares returned (9.04)%. The Fund’s benchmark, the ICE BofA US Municipal Securities Index, returned (9.28)% for the same period.

Returns for the Fund’s respective share classes differ from the benchmark index based on individual share-class expenses.

Describe the market environment.

The broad U.S. municipal bond market returned (9.28%) for the first half of 2022 as gauged by the Underlying Index. The 10-year U.S. Treasury yield reached as high as 3.49% before finishing the period at 3.01%, an increase of 149 basis points from its 1.52% starting point at the end of 2021. Market volatility persisted as the focus of investors toggled between persistently high inflation prints and growing fears around a potential recession. Against a backdrop of historically high inflation, Fed rate hikes and rising Treasury yields, the AAA municipal yield curve moved higher and flattened over the six months.

With respect to monetary policy, the Fed signaled at the beginning of June 2022 that 50 basis point increases in its benchmark overnight lending rate in June and July would be sufficient near-term tightening under the assumption that monthly inflation prints would decelerate. However, surprisingly strong consumer price index data released the week prior to the June 15th Federal Open Market Committee meeting forced the Fed to accelerate its hiking path, raising rates by 75 basis points. While the committee “does not expect moves of this size to be common,” it raised guidance for the path of hikes for the rest of the year and indicate it will be looking for compelling evidence that inflation pressures are abating before considering a pause. Importantly, the Fed’s Summary of Economic Projections revealed an acknowledgment that restoring price stability will require some economic pain, likely in the form of higher unemployment.

Elsewhere on the economic data front, May 2022 saw a solid 390,000 jobs gained, although this reflected a slowdown from the 516,000 gained in April 2022. Unemployment remained little changed at 3.62% for the third month in a row as the pace of recovery continues to slow since the start of the year. Other parts of the economy also showed moderation, with retail sales, housing starts, and purchasing manager index data all softening. Additionally, consumer confidence has fallen precipitously over the course of the first half of the year as inflation takes its toll on household spending and sentiment.

Describe recent portfolio activity.

During the period, the Fund maintained its objective of seeking to provide investment results that correspond to the total return performance of the Index by selecting securities in accordance with their relative proportion within the Index. Other factors considered in security selection included transaction costs and maturity.

Describe portfolio positioning at period end.

The Fund remained positioned to attempt to match the risk characteristics of the Index, irrespective of the market’s future direction.

The views expressed reflect the opinions of BlackRock as of the date of this report and are subject to change based on changes in market, economic or other conditions. These views are not intended to be a forecast of future events and are no guarantee of future results.

Performance

N/A — Not applicable as the share class and index do not have a sales charge.

Past performance is not an indication of future results.

Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.

Expense Example

See “Disclosure of Expenses” for further information on how expenses were calculated.

Portfolio Information

Investment Objective

iShares Short-Term TIPS Bond Index Fund’s (the “Fund”) investment objective is to seek to track the investment results of an index composed of U.S. 0-5 Year Treasury Inflation-Protected Securities (TIPS).

Portfolio Management Commentary

How did the Fund perform?

For the six-month period ended June 30, 2022, the Fund’s Institutional Shares returned (1.41)%, Class K Shares returned (1.39)% and Investor A shares returned (1.53)%. The Fund’s benchmark, the Bloomberg U.S. Treasury Inflation-Protected Securities (TIPS) 0-5 Years Index (Series-L), (the “Underlying Index”), returned (1.40)% for the same period.

Returns for the Fund’s respective share classes differ from the Underlying Index based on individual share-class expenses.

What factors influenced performance?

Prices for “TIPS” are influenced by changes in inflation expectations as well as the direction of nominal Treasury yields. For the six-month period, the Bloomberg U.S. TIPS Index posted a return of (8.92%) while the Fund’s benchmark, the Bloomberg U.S. TIPS 0-5 year Index (Series-L), returned (1.40%), with returns for both indexes limited by rising longer-term nominal Treasury yields.

For much of the period, investors primarily focused on the impact of Russia’s war on Ukraine and the Fed hiking its benchmark overnight lending rate, along with persistently high inflation readings. The May consumer price index (“CPI”) report showed another robust gain in core and headline inflation, with the latter printing at its highest level in 40 years. The labor market continued its strong recovery, with the April 2022 nonfarm payroll report showing 428,000 new jobs, above market expectations of 380,000, and the May 2022 report adding 390,000 jobs versus the anticipated 318,000.

Reflecting concern over historically high inflation, the Federal Open Market Committee raised short-term rates by 50 basis points on May 4, 2022 and another 75 basis points on June 15, 2022. Chairman Jerome Powell stated that the committee was “determined, resolved, but flexible” in this highly uncertain environment to bring inflation down. The Summary of Economic Projections revealed a committee that acknowledges the process to restoring price stability will be painful. The committee will continue to remain focused on preventing higher inflation from getting entrenched with the labor market now extremely tight.

The Master Portfolio held a small amount of cash committed for pending transactions. The cash balance did not have a material impact on performance.

Describe recent portfolio activity.

During the period, the Fund maintained its objective of seeking to provide investment results that correspond to the total return performance of the benchmark Index by selecting securities in accordance with their relative proportion within the Index. Other factors considered in security selection included transaction costs and maturity.

Describe portfolio positioning at period end.

The Fund remains positioned to attempt to match the risk and return characteristics of the Index, irrespective of the future direction of inflation expectations.

The views expressed reflect the opinions of BlackRock as of the date of this report and are subject to change based on changes in market, economic or other conditions. These views are not intended to be a forecast of future events and are no guarantee of future results.

Performance

Past performance is not an indication of future results.

Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.

Expense Example

See “Disclosure of Expenses” for further information on how expenses were calculated.

Portfolio Information

Investment Objective

iShares MSCI EAFE International Index Fund’s (the “Fund”) investment objective is to match the performance of the MSCI EAFE Index (Europe, Australasia, Far East) (the “MSCI EAFE Index”) in U.S. dollars with net dividends as closely as possible before the deduction of Fund expenses.

Portfolio Management Commentary

How did the Fund perform?

For the six-month period ended June 30, 2022, the Fund’s Institutional Shares returned (19.01)%, Investor A Shares returned (19.14)%, Investor P Shares returned (19.14)%, and Class K Shares returned (18.99)%. The MSCI EAFE Index returned (19.57)% for the same period.

Returns for the Fund’s respective share classes differ from the MSCI EAFE Index based on individual share-class expenses.

Describe the market environment.

As developed markets started recovering from the Omicron Variant of the COVID-19 pandemic, investors’ attention shifted to rising inflation rates, the spike in commodity prices, and the financial and economic implications of the Russian invasion of Ukraine in February 2022. Those concerns dampened investors’ sentiment and market performance over the first quarter.

In response to rising inflation rates, the European Central Bank (“ECB”) announced their plan to end bond purchasing by the end of September 2022. Annual inflation in the eurozone rose from 5.9% in February 2022 to 7.5% in March 2022, fueled by increasing commodity prices. In the U.K., the Bank of England raised the interest rate by 0.5% over the quarter on top of an additional 0.15% raise in December 2021. The U.K. equity market proved more resilient than its developed markets peers, supported by its exposure to energy and materials.

In Japan, the manufacturing sector continued to suffer from supply chain disruption and the semiconductor shortage. The yen weakened and reached a six-year low against the U.S. dollar in March 2022.

Rising inflation and recession fears weighed down on developed markets performance. Global geopolitical tension intensified as the war in Ukraine continued with no sign of resolution. European countries were directly impacted by the reduction in gas supply from Russia and increased gas prices — peaking in the first half of June 2022 and driving inflation higher. Germany announced its energy emergency plan to prioritize industrial users with the allocation of gas supply. Similarly, the U.K. unveiled its new measures to help households facing larger energy bills in the upcoming fall.

As a result of the ongoing elevated inflation, the Bank of England raised the U.K. base rate to 1.25% in June 2022 while the ECB indicated a first-rate hike will likely be in July 2022 along with an end to asset purchase plan early in Q3 2022. In Japan, the Yen weakened against the U.S. dollar breaching the 130 level for the first time in the last two decades as Bank of Japan kept its accommodative monetary policy unchanged.

Describe recent portfolio activity.

During the six-month period, as changes were made to the composition of the MSCI EAFE Index, the Fund purchased and sold securities to maintain its objective of matching the risks and return of the benchmark index.

Describe portfolio positioning at period end.

The Fund remains positioned to match the risk characteristics of the MSCI EAFE Index, irrespective of the market’s future direction.

The views expressed reflect the opinions of BlackRock as of the date of this report and are subject to change based on changes in market, economic or other conditions. These views are not intended to be a forecast of future events and are no guarantee of future results.

Performance

N/A — Not applicable as the share class and index do not have a sales charge.

Past performance is not an indication of future results.

Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.

Expense Example

See “Disclosure of Expenses” for further information on how expenses were calculated.

Portfolio Information

Investment Objective

iShares Russell 2000 Small-Cap Index Fund’s (the “Fund”) investment objective is to match the performance of the Russell 2000^® Index (the “Underlying Index”) as closely as possible before the deduction of Fund expenses.

Portfolio Management Commentary

How did the Fund perform?

For the six-month period ended June 30, 2022, the Fund’s Institutional Shares returned (23.41)%, Investor A Shares returned (23.46)%, Investor P Shares returned (23.50)%, and Class K Shares returned (23.37)%. The Underlying Index returned (23.43)% for the same period.

Returns for the Fund’s respective share classes differ from the benchmark index based on individual share-class expenses. The Fund invests all of its assets in Master Small Cap Index Series (the “Series”), a series of Quantitative Master Series LLC.

Describe the market environment.

Geopolitical tension after the Russian invasion of Ukraine in February 2022 fueled existing concerns over rising inflation, interest rate hikes, and rallying commodity prices. On the other hand, economic data in the United States remained strong with robust employment numbers and corporate earnings results. This provided comfort to investors but added to U.S. policy makers challenges. Investors were concerned that the Fed may dampen growth in an effort to get inflation under control.

Commodity prices spiked in the first quarter 2022 and pushed expectations for a higher inflation rate. The Fed hiked the interest rate by 25 basis points and signaled hikes at all six-remaining meetings for the year in efforts to tackle the highest inflation rate in four decades.

Concerns about high inflation, growth outlook and recession fears increased in the United States during the second quarter. While the unemployment rate remained low and wage growth strong, consumer sentiment went down as consumers struggled with higher prices and borrowing costs. The increased expectation of an interest rate hike weighed down on U.S. equity market valuations.

As the Fed continued to grapple with inflation, their messaging evolved over the second quarter 2022. Initially, Chairman Jerome Powel adopted a more hawkish tone stating that they would not hesitate to raise interest rates beyond neutral to achieve its inflation target and would be willing to accept an increase in unemployment rate. But as risks to growth increased over the quarter and recession fears intensified, the number and magnitude of future rate hikes beyond July 2022 remained unclear.

Describe recent portfolio activity.

During the six-month period, as changes were made to the composition of the Underlying Index, the Series purchased and sold securities to maintain its objective of matching the risks and return of the benchmark index.

Describe portfolio positioning at period end.

The Series remains positioned to match the risk characteristics of its benchmark index, irrespective of the market’s future direction.

The views expressed reflect the opinions of BlackRock as of the date of this report and are subject to change based on changes in market, economic or other conditions. These views are not intended to be a forecast of future events and are no guarantee of future results.

Performance

N/A — Not applicable as the share class and index do not have a sales charge.

Past performance is not an indication of future results.

Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.

Expense Example

See “Disclosure of Expenses” for further information on how expenses were calculated.

About Fund Performance

Institutional and Class K Shares are not subject to any sales charge. These shares bear no ongoing distribution or service fees and are available only to certain eligible investors.

On November 19, 2018, the iShares Municipal Bond Index Fund acquired all of the assets and assumed certain stated liabilities, of the State Farm Tax Advantaged Bond Fund (the “Predecessor Fund”), a series of State Farm Mutual Fund Trust, in a tax-free reorganization (the “Reorganization”). The Predecessor Fund is the performance and accounting survivor of the Reorganization. Accordingly, information provided herein for periods prior to the Reorganization is that of the Predecessor Fund. See Note 1 of the Notes to Financial Statements for additional information regarding the Reorganization.

Institutional and Class K Shares performance of iShares Municipal Bond Index Fund shown prior to the Institutional and Class K Shares inception date of November 19, 2018 is that of Investor A Shares, which reflect the performance of Premier Shares of the Predecessor Fund. The performance of iShares Municipal Bond Index Fund’s Institutional and Class K Shares would be substantially similar to Investor A Shares because Institutional Shares, Class K Shares and Investor A Shares invest in the same portfolio of securities and performance would only differ to the extent that Institutional Shares, Class K Shares and Investor A Shares have different expenses. The actual returns of Institutional and Class K Shares would have been higher than those of the Investor A Shares because Institutional and Class K Shares have lower expenses than the Investor A Shares.

Investor A Shares are not subject to any sales charge and bear no ongoing distribution fee. These shares are subject to an ongoing service fee of 0.25% per year. These shares are generally available through financial intermediaries. Investor A Shares performance of iShares Municipal Bond Index Fund shown prior to the Reorganization is that of the Premier Shares of the Predecessor Fund.

Investor P Shares (available in iShares MSCI EAFE International Index Fund and iShares Russell 2000 Small-Cap Index Fund) are subject to a maximum initial sales charge (front-end load) of 5.25% and a service fee of 0.25% per year (but no distribution fee). These shares are only available to investors purchasing shares through registered representatives of an insurance company’s broker-dealer that has entered into an agreement with iShares MSCI EAFE International Index Fund and iShares Russell 2000 Small-Cap Index Fund’s distributor to offer such shares. Investor P Share performance of iShares MSCI EAFE International Index Fund and iShares Russell 2000 Small-Cap Index Fund shown prior to the Investor P Shares inception date of August 6, 2018 is that of Institutional Shares (which have no distribution or service fees) and was restated to reflect Investor P Shares fees.

Investor P Shares (available in iShares Municipal Bond Index Fund) are subject to a maximum initial sales charge (front-end load) of 4.00% and a service fee of 0.25% per year (but no distribution fee). Certain redemptions of these shares may be subject to a contingent deferred sales charge (“CDSC”) where no initial sales charge was paid at the time of purchase. These shares are only available to investors purchasing shares through registered representatives of an insurance company’s broker-dealer that has entered into an agreement with the Fund’s distributor to offer such shares. Investor P Shares performance shown prior to the Reorganization is that of the Premier Shares of the Predecessor Fund.

Past performance is not an indication of future results. Financial markets have experienced extreme volatility and trading in many instruments has been disrupted. These circumstances may continue for an extended period of time and may continue to affect adversely the value and liquidity of each Fund’s investments. As a result, current performance may be lower or higher than the performance data quoted. Refer to blackrock.com to obtain performance data current to the most recent month-end. Performance results do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or the redemption of Fund shares. Figures shown in the performance table(s) assume reinvestment of all distributions, if any, at net asset value (“NAV”) on the ex-dividend date or payable date, as applicable. Investment return and principal value of shares will fluctuate so that shares, when redeemed, may be worth more or less than their original cost. Distributions paid to each class of shares will vary because of the different levels of service, distribution and transfer agency fees applicable to each class, which are deducted from the income available to be paid to shareholders.

BlackRock Fund Advisors, the investment adviser of iShares Municipal Bond Index Fund and BlackRock Advisors, LLC, the investment adviser of iShares Short-Term TIPS Bond Index Fund, iShares MSCI EAFE International Index Fund and iShares Russell 2000 Small-Cap Index Fund (the “Manager”), each has contractually and/or voluntarily agreed to waive and/or reimburse a portion of each Fund’s expenses. Without such waiver(s) and/or reimbursement(s), each Fund’s performance would have been lower. With respect to each Fund’s voluntary waiver(s), if any, the Manager is under no obligation to waive and/or reimburse or to continue waiving and/or reimbursing its fees and such voluntary waiver(s) may be reduced or discontinued at any time. With respect to each Fund’s contractual waiver(s), if any, the Manager is under no obligation to continue waiving and/or reimbursing its fees after the applicable termination date of such agreement. See the Notes to Financial Statements for additional information on waivers and/or reimbursements.

The standardized 30-day yield includes the effects of any waivers and/or reimbursements. The unsubsidized 30-day yield excludes the effects of any waivers and/or reimbursements.

Disclosure of Expenses

Shareholders of each Fund may incur the following charges: (a) transactional expenses, such as sales charges; and (b) operating expenses, including investment advisory fees, service and distribution fees, including 12b-1 fees, acquired fund fees and expenses, and other fund expenses. The expense examples shown (which are based on a hypothetical investment of $1,000 invested at the beginning of the period and held through the end of the period) are intended to assist shareholders both in calculating expenses based on an investment in each Fund and in comparing these expenses with similar costs of investing in other mutual funds.

The expense examples provide information about actual account values and actual expenses. Annualized expense ratios reflect contractual and voluntary fee waivers, if any. In order to estimate the expenses a shareholder paid during the period covered by this report, shareholders can divide their account value by $1,000 and then multiply the result by the number corresponding to their Fund and share class under the heading entitled “Expenses Paid During the Period.”

The expense examples also provide information about hypothetical account values and hypothetical expenses based on a Fund’s actual expense ratio and an assumed rate of return of 5% per year before expenses. In order to assist shareholders in comparing the ongoing expenses of investing in these Funds and other funds, compare the 5% hypothetical examples with the 5% hypothetical examples that appear in shareholder reports of other funds.

The expenses shown in the expense examples are intended to highlight shareholders’ ongoing costs only and do not reflect transactional expenses, such as sales charges, if any. Therefore, the hypothetical examples are useful in comparing ongoing expenses only and will not help shareholders determine the relative total expenses of owning different funds. If these transactional expenses were included, shareholder expenses would have been higher.

Derivative Financial Instruments

The Funds may invest in various derivative financial instruments. These instruments are used to obtain exposure to a security, commodity, index, market, and/or other assets without owning or taking physical custody of securities, commodities and/or other referenced assets or to manage market, equity, credit, interest rate, foreign currency exchange rate, commodity and/or other risks. Derivative financial instruments may give rise to a form of economic leverage and involve risks, including the imperfect correlation between the value of a derivative financial instrument and the underlying asset, possible default of the counterparty to the transaction or illiquidity of the instrument. The Funds’ successful use of a derivative financial instrument depends on the investment adviser’s ability to predict pertinent market movements accurately, which cannot be assured. The use of these instruments may result in losses greater than if they had not been used, may limit the amount of appreciation a Fund can realize on an investment and/or may result in lower distributions paid to shareholders. The Funds’ investments in these instruments, if any, are discussed in detail in the Notes to Financial Statements.