Share class (Symbol): Investor Shares (LTRXX)

WESTERN ASSET

INSTITUTIONAL U.S. TREASURY RESERVES

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 and other information about the fund, including the fund’s statement of additional information and shareholder reports, online at www.franklintempleton.com/moneymarketfundsliterature. You can also get this information at no cost by calling the fund at 1-877-721-1926 or 1-203-703-6002 or by sending an e-mail request to prospectus@franklintempleton.com, or from your financial intermediary. The fund’s Prospectus and statement of additional information, each dated December  29, 2023 (as may be amended or supplemented from time to time), and the independent registered public accounting firm’s report and financial statements in the fund’s annual report to shareholders, dated August 31, 2023, are incorporated by reference into this Summary Prospectus.

Investment objective

The fund’s investment objective is to provide shareholders with liquidity and as high a level of current income from U.S. government obligations as is consistent with preservation of capital.

Fees and expenses of the fund

The accompanying table describes the fees and expenses that you may pay if you buy, hold and sell Investor Shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.

Example

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes:

Although your actual costs may be higher or lower, based on these assumptions your costs would be:

The fund is a feeder fund that invests in securities through an underlying mutual fund, U.S. Treasury Reserves Portfolio, which has the same investment objective and strategies as the fund. This structure is sometimes known as a “master/feeder” structure.

Principal investment strategies

The fund is a money market fund that, under normal circumstances, invests at least 80% of its net assets in U.S. Treasury obligations. In addition, the fund may invest in repurchase agreements that are fully collateralized by U.S. Treasury obligations or cash. U.S. Treasury obligations include, without limitation, U.S. Treasury bills, notes and bonds; STRIPS, which are individual interest and principal components of eligible Treasury notes and bonds that are traded as separate securities; and TIPS, which are inflation-protected securities issued by the U.S. Treasury, the principal of which increases with inflation and decreases with deflation, as measured by the Consumer Price Index.

The fund holds all of its assets in U.S. Treasury obligations, repurchase agreements that are fully collateralized by U.S. Treasury obligations, and cash. Therefore, the fund meets the requirement under Rule 2a-7 under the Investment Company Act of 1940, as amended (the “1940 Act”), that a government money market fund invest at least 99.5% of its total assets in U.S. government securities, cash, and/or repurchase agreements that are fully collateralized by U.S. government securities or cash. “Government securities” means any securities issued or guaranteed as to principal or interest by the United States, or by a person controlled or supervised by and acting as an instrumentality of the Government of the United States pursuant to authority granted by the Congress of the United States; or any certificate of deposit for any of the foregoing.

As a government money market fund, the fund tries to maintain a share price of $1.00. Pursuant to Rule 2a-7 under the 1940 Act, the fund must follow strict rules as to the quality, liquidity, diversification and maturity of its investments.

The fund may hold cash for cash management and defensive purposes. During unusual market conditions, the fund may hold up to 100% of its assets in cash. Although the fund intends to invest in U.S. government securities, an investment in the fund is neither insured nor guaranteed by the U.S. government.

Principal risks

You could lose money by investing in the fund. Although the fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the fund is not a bank account and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The fund’s sponsor is not required to reimburse the fund for losses, and you should not expect that the sponsor will provide financial support to the fund at any time, including during periods of market stress.

During periods of market stress, there could be significant redemptions from money market funds in general, potentially driving the market prices of money market instruments down and adversely affecting market liquidity.

The fund could underperform other short-term debt instruments or money market funds, or you could lose money, as a result of risks such as:

Market and interest rate risk. The market prices of securities held by the fund may go up or down, sometimes rapidly or unpredictably. While the fund seeks to maintain a $1.00 share price, if the market prices of the fund’s securities fall, the value of your investment in the fund could decline. The market price of a security may fall due to general market conditions, such as real or perceived adverse economic or political conditions or trends, tariffs and trade disruptions, inflation, substantial economic downturn or recession, changes in interest rates, lack of liquidity in the bond markets or adverse investor sentiment.

Market prices will generally go down when interest rates rise. A rise in rates tends to have a greater impact on the prices of longer term securities. A general rise in interest rates may cause investors to move out of fixed income securities on a large scale, which could adversely affect the price and liquidity of fixed income securities and could also result in increased redemptions from the fund. The fund may face a heightened level of interest rate risk due to changes in monetary policy. When interest rates go down, the fund’s yield will decline. Also, when interest rates decline, investments made by the fund may pay a lower interest rate, which would reduce the income received by the fund. Recently, there have been inflationary price movements, which have caused the fixed income securities markets to experience heightened levels of interest rate volatility and liquidity risk. The U.S. Federal Reserve has been raising interest rates from historically low levels. It may continue to raise interest rates. In addition, changes in monetary policy may exacerbate the risks associated with changing interest rates. Any additional interest rate increases in the future could cause the value of the fund’s holdings to decrease. It cannot be predicted when inflation will return to more normalized levels or how long financial authorities will counter inflationary pressures with monetary tightening.

Market events risk. The market values of securities or other assets will fluctuate, sometimes sharply and unpredictably, due to factors such as economic events, governmental actions or

intervention, actions taken by the U.S. Federal Reserve or foreign central banks, market disruptions caused by trade disputes, labor strikes or other factors, political developments, armed conflicts, economic sanctions and countermeasures in response to sanctions, major cybersecurity events, the global and domestic effects of widespread or local health, weather or climate events, and other factors that may or may not be related to the issuer of the security or other asset. Economies and financial markets throughout the world are increasingly interconnected. Economic, financial or political events, trading and tariff arrangements, public health events, terrorism, wars, natural disasters and other circumstances in one country or region could have profound impacts on global economies or markets. As a result, whether or not the fund invests in securities of issuers located in or with significant exposure to the countries or markets directly affected, the value and liquidity of the fund’s investments may be negatively affected. Following Russia’s invasion of Ukraine in 2022, Russian stocks lost all, or nearly all, of their market value. Other securities or markets could be similarly affected by past or future geopolitical or other events or conditions. Furthermore, events involving limited liquidity, defaults, non-performance or other adverse developments that affect one industry, such as the financial services industry, or concerns or rumors about any events of these kinds, have in the past and may in the future lead to market-wide liquidity problems, may spread to other industries, and could negatively affect the value and liquidity of the fund’s investments.

The long-term impact of the COVID-19 pandemic and its subsequent variants on economies, markets, industries and individual issuers is not known. Some sectors of the economy and individual issuers have experienced or may experience particularly large losses. Periods of extreme volatility in the financial markets, reduced liquidity of many instruments, increased government debt, inflation, and disruptions to supply chains, consumer demand and employee availability, may continue for some time.

Raising the ceiling on U.S. government debt has become increasingly politicized. Any failure to increase the total amount that the U.S. government is authorized to borrow could lead to a default on U.S. government obligations, with unpredictable consequences for economies and markets in the U.S. and elsewhere. Recently, inflation and interest rates have increased and may rise further. These circumstances could adversely affect the value and liquidity of the fund’s investments, impair the fund’s ability to satisfy redemption requests, and negatively impact the fund’s performance.

Credit risk. An issuer or other obligor (such as a party providing insurance or other credit enhancement) of a security held by the fund or a counterparty to a financial contract with the fund may default or its credit may be downgraded or perceived to be less creditworthy, or the value of assets underlying a security may decline, causing the value of your investment to decline. Changes in actual or perceived creditworthiness may occur quickly. The fund could be delayed or hindered in its enforcement of rights against an issuer, guarantor or counterparty.

Yield risk. The amount of income received by the fund will go up or down depending on variations in short-term interest rates, and when interest rates are very low or negative the fund’s expenses could absorb all or a significant portion of the fund’s income. If interest rates increase, the fund’s yield may not increase proportionately, if for example, the fund’s manager

discontinued any temporary voluntary fee limitation or recouped amounts previously waived and/or reimbursed.

Repurchase agreements risk. Repurchase agreements could involve certain risks in the event of default or insolvency of the seller, including losses and possible delays or restrictions upon the fund’s ability to dispose of the underlying securities. To the extent that, in the meantime, the value of the securities that the fund has purchased has decreased, the fund could experience a loss. The use of repurchase agreements may produce income that is not exempt from state personal income tax.

Portfolio management risk. The value of your investment may decrease if the subadviser’s judgment about the quality, relative yield, value or market trends affecting a particular security, industry, sector or region, or about interest rates or other market factors, is incorrect or does not produce the desired results, or if there are imperfections, errors or limitations in the tools and data used by the subadviser. In addition, the fund’s investment strategies or policies may change from time to time. Those changes may not lead to the results intended by the subadviser and could have an adverse effect on the value or performance of the fund.

Illiquidity risk. The fund may make investments that are illiquid or that become illiquid after purchase. The liquidity and value of investments can deteriorate rapidly, and they may become difficult or impossible to sell, particularly during times of market turmoil. Illiquid investments may also be volatile and difficult to value. Markets may become illiquid quickly. Markets may become illiquid when, for instance, there are few, if any, interested buyers or sellers or when dealers are unwilling or unable to make a market for certain securities, including U.S. Treasury securities. During times of market turmoil, there may be few or no buyers or sellers for securities in entire asset classes. If the fund is forced to sell an illiquid investment to meet redemption requests or other cash needs, or to try to limit losses, the fund may be forced to sell at a substantial loss or may not be able to sell at all.

Valuation risk. The sales price the fund could receive for any particular portfolio investment may differ from the fund’s valuation of the investment, particularly for securities that trade in thin or volatile markets or that are valued using a fair value methodology. These differences may increase significantly and affect fund investments more broadly during periods of market volatility. Investors who purchase or redeem fund shares on days when the fund is holding fair-valued securities may receive fewer or more shares or lower or higher redemption proceeds than they would have received if the fund had not fair-valued securities or had used a different valuation methodology. The fund’s ability to value its investments may be impacted by technological issues and/or errors by pricing services or other third party service providers. The valuation of the fund’s investments involves subjective judgment, which may prove to be incorrect.

Cybersecurity risk. Like other funds and business enterprises, the fund, the manager, the subadviser and their service providers are subject to the risk of cyber incidents occurring from time to time. Cybersecurity incidents, whether intentionally caused by third parties or otherwise, may allow an unauthorized party to gain access to fund assets, fund or customer data (including private shareholder information) or proprietary information, cause the fund, the manager, the subadviser and/or their service providers (including, but not limited to, fund accountants,

custodians, sub-custodians, transfer agents and financial intermediaries) to suffer data breaches, data corruption or loss of operational functionality, or prevent fund investors from purchasing, redeeming or exchanging shares, receiving distributions or receiving timely information regarding the fund or their investment in the fund. The fund, the manager, and the subadviser have limited ability to prevent or mitigate cybersecurity incidents affecting third party service providers, and such third party service providers may have limited indemnification obligations to the fund, the manager, and/or the subadviser. Cybersecurity incidents may result in financial losses to the fund and its shareholders, and substantial costs may be incurred in order to prevent or mitigate any future cybersecurity incidents. Issuers of securities in which the fund invests are also subject to cybersecurity risks, and the value of these securities could decline if the issuers experience cybersecurity incidents.

New ways to carry out cyber attacks continue to develop. There is a chance that some risks have not been identified or prepared for, or that an attack may not be detected, which puts limitations on the fund’s ability to plan for or respond to a cyber attack.

These and other risks are discussed in more detail in the Prospectus or in the Statement of Additional Information.

Performance

The accompanying bar chart and table provide some indication of the risks of investing in the fund. The bar chart shows changes in the fund’s performance from year to year for Investor Shares. The table shows the average annual total returns of Investor Shares. Performance for classes other than those shown may vary from the performance shown to the extent the expenses for those classes differ. The fund makes updated performance information available at www.franklintempleton.com/moneymarketfunds (select fund and share class), or by calling the fund at 1-877-721-1926 or 1-203-703-6002.

The fund’s past performance is not necessarily an indication of how the fund will perform in the future.

Best Quarter (12/31/2022): 0.84    Worst Quarter (12/31/2021): 0.00

The year-to-date return as of the most recent calendar quarter, which ended 09/30/2023, was 3.58

Management

Investment manager: Franklin Templeton Fund Adviser, LLC (“FTFA”) (formerly known as Legg Mason Partners Fund Advisor, LLC)

Subadviser: Western Asset Management Company, LLC (“Western Asset”)

Purchase and sale of fund shares

In general, you may purchase, redeem or exchange shares of the fund during fund business hours on any day on which both the New York Stock Exchange and the Federal Reserve Bank of New York are open for business, subject to certain exceptions.

The fund’s initial and subsequent investment minimums for Investor Shares generally are set forth in the accompanying table:

Investor Shares are available only through financial intermediaries. Your Service Agent may impose higher or lower investment minimums, or may impose no minimum investment requirement. “Service Agents” are banks, brokers, dealers, insurance companies, investment advisers, financial consultants or advisers, mutual fund supermarkets and other financial intermediaries that have entered into an agreement with the distributor to sell shares of the fund.

The fund normally calculates its net asset value as of each hour from 8:00 a.m. (Eastern time) until its close of business (normally 2:00 p.m. (Eastern time)) on each fund business day. The fund may close early under certain circumstances. For more information, please contact your financial intermediary, or contact the fund by phone (1-877-721-1926 or 1-203-703-6002).

Tax information

The fund’s distributions are generally taxable as ordinary income or capital gains.

Payments to broker/dealers and other financial intermediaries

The fund’s related companies pay Service Agents for the sale of fund shares, shareholder services and other purposes. These payments create a conflict of interest by influencing your Service Agent or its employees or associated persons to recommend the fund over another investment. Ask your financial adviser or salesperson or visit your Service Agent’s or salesperson’s website for more information.

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		Franklin Distributors, LLC One Franklin Parkway San Mateo, CA 94403-1906 franklintempleton.com   Western Asset Institutional U.S. Treasury Reserves

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