Summary Prospectus by Investment Company (Form 497K)

WESTERN ASSET

INFLATION INDEXED PLUS

BOND FUND

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, shareholder reports and fund financial statements, online at https://www.franklintempleton.com/prospectus. You can also get this information at no cost by calling the fund at 877-6LM-FUND/656-3863 or by sending an e-mail request to [email protected], or from your financial intermediary. The fund's Prospectus and statement of additional information, each dated May 1, 2026 (as may be amended or supplemented from time to time), and the independent registered public accounting firm's report and financial statements for the fiscal year ended December 31, 2025, as filed on Form N-CSR, are incorporated by reference into this Summary Prospectus.

Investment objective

Maximize total return, 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 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.

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $100,000 in certain funds distributed through Franklin Distributors, LLC ("Franklin Distributors" or the "Distributor"), the fund's distributor. More information about these and other discounts is available from your Service Agent, in the fund's Prospectus on page 31 under the heading "Additional information about each share class," in the appendix titled "Appendix: Waivers and Discounts Available from Certain Service Agents" on page A-1 of the fund's Prospectus and in the fund's Statement of Additional Information ("SAI") on page 90 under the heading "Sales Charge Waivers and Reductions for Class A Shares." "Service Agents" include 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.

If you purchase Class I shares or Class IS shares through a Service Agent acting solely as an agent on behalf of its customers, that Service Agent may charge you a commission. Such commissions, if any, are not charged by the fund and are not reflected in the fee table or expense example 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:

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 shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 41% of the average value of its portfolio.

Principal investment strategies

Under normal market conditions, the fund invests at least 80% of its net assets, including the amount of borrowing for investment purposes, if any, in inflation-indexed fixed income securities and at least 70% of its net assets in U.S. Treasury Inflation Protected Securities.

The subadvisers use fundamental investment techniques to select issues. Although the fund may invest in securities of any maturity, the fund normally expects to maintain a dollar-weighted average effective duration, as estimated by the fund's subadvisers, within 3 years of that of its benchmark, the Bloomberg U.S. Treasury: U.S. TIPS. Effective duration seeks to measure the expected sensitivity of market price to changes in interest rates, taking into account the anticipated effects of structural complexities (for example, some bonds can be prepaid by the issuer).

The fund may sell protection in connection with credit default swaps relating to corporate debt securities. It is currently expected that the notional amount of the credit default swaps will not exceed 40% of the fund's net assets, although such exposure may exceed 40% from time to time.

The fund is expected to maintain a dollar-weighted average credit quality of at least A/A.

In addition, under normal market conditions, at the time of purchase:

The fund considers a security to be rated below investment grade if it is not rated in the Baa/BBB categories or above by at least one Nationally Recognized Statistical Rating Organization ("NRSRO") or is unrated and of comparable quality as determined by the subadvisers. Securities rated below investment grade are commonly known as "junk bonds" or "high yield securities."

The fund may also enter into various exchange-traded and over-the-counter derivative transactions for both hedging and non-hedging purposes, including for purposes of enhancing returns. These derivative transactions include, but are not limited to, futures, options, swaps, foreign currency futures and forwards.

In particular, the fund may use interest rate swaps, credit default swaps (including buying and selling credit default swaps on individual securities and/or baskets of securities), options (including options on credit default swaps) and futures contracts to a significant extent, although

the amounts invested in these instruments may change from time to time. Other instruments may also be used to a significant extent from time to time.

Principal risks

Risk is inherent in all investing. The value of your investment in the fund, as well as the amount of return you receive on your investment, may fluctuate significantly. You may lose part or all of your investment in the fund or your investment may not perform as well as other similar investments. An investment in the fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or by any bank or government agency. The following is a summary description of certain risks of investing in the fund. The relative significance of the risks of investing in the fund may change over time.

Market and interest rate risk. The market prices of securities held by the fund may go up or down, sometimes rapidly or unpredictably. If the market prices of the fund's securities fall, the value of your investment in the fund will 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. Changes in market conditions will not typically have the same impact on all types of securities.

The value of your investment will generally go down when interest rates rise. A rise in rates tends to have a greater impact on the prices of longer term or duration 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. Recently, there have been inflationary price movements. As a result, fixed income securities markets may experience heightened levels of interest rate volatility and liquidity risk. The U.S. government and the U.S. Federal Reserve, as well as certain foreign governments and central banks, have from time to time taken steps to support financial markets. The U.S. government and the U.S. Federal Reserve may, conversely, reduce market support activities. This and other government intervention may not work as intended, particularly if the efforts are perceived by investors as being unlikely to achieve the desired results. Changes in government activities in this regard, such as changes in interest rate policy, can negatively affect financial markets generally, increase market volatility and reduce the value and liquidity of securities in which the fund invests.

The maturity of a security may be significantly longer than its duration. A security's maturity and other features may be more relevant than its duration in determining the security's sensitivity to other factors affecting the issuer or markets generally such as changes in credit quality or in the yield premium that the market may establish for certain types of securities.

Credit risk. If an issuer or guarantor of a security held by the fund or a counterparty to a financial contract with the fund defaults or its credit is downgraded, or is perceived to be less creditworthy, or if the value of the assets underlying a security declines, the value of your investment will typically 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. Subordinated securities (meaning securities that rank below other securities with respect to claims on the issuer's assets) are more likely to suffer a credit loss

than non-subordinated securities of the same issuer and will be disproportionately affected by a default, downgrade or perceived decline in creditworthiness.

High yield ("junk") bonds risk. High yield bonds are generally subject to greater credit risks than higher-grade bonds, including the risk of default on the payment of interest or principal. High yield bonds are considered speculative, typically have lower liquidity and are more difficult to value than higher grade bonds. High yield bonds tend to be volatile and more susceptible to adverse events, credit downgrades and negative sentiments and may be difficult to sell at a desired price, or at all, during periods of uncertainty or market turmoil.

Derivatives risk. Using derivatives can increase fund losses and reduce opportunities for gains, such as when market prices, interest rates, currencies, or the derivatives themselves behave in a way not anticipated by the fund's subadviser. Using derivatives also can have a leveraging effect and increase fund volatility. Certain derivatives have the potential for unlimited loss, regardless of the size of the initial investment. Derivatives may not be available at the time or price desired, may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. Derivatives are generally subject to the risks applicable to the assets, rates, indices or other indicators underlying the derivative. The value of a derivative may fluctuate more than the underlying assets, rates, indices or other indicators to which it relates. Use of derivatives may have different tax consequences for the fund than an investment in the underlying asset, and those differences may affect the amount, timing and character of income distributed to shareholders. The U.S. government and non-U.S. governments have adopted and implemented regulations governing derivatives markets, including mandatory clearing of certain derivatives, margin and reporting requirements. The ultimate impact of the regulations remains unclear. Additional regulation of derivatives may make derivatives more costly, limit their availability or utility, otherwise adversely affect their performance or disrupt markets.

Credit default swap contracts involve heightened risks and may result in losses to the fund. Credit default swaps may be illiquid and difficult to value. When the fund sells credit protection via a credit default swap, credit risk increases since the fund has exposure to both the issuer whose credit is the subject of the swap and the counterparty to the swap.

Leverage risk. The value of your investment may be more volatile if the fund borrows or uses instruments, such as derivatives, that have a leveraging effect on the fund's portfolio. Other risks described in the Prospectus also will be compounded because leverage generally magnifies the effect of a change in the value of an asset and creates a risk of loss of value on a larger pool of assets than the fund would otherwise have had. The fund may also have to sell assets at inopportune times to satisfy its obligations created by the use of leverage or derivatives. The use of leverage is considered to be a speculative investment practice and may result in the loss of a substantial amount, and possibly all, of the fund's assets. In addition, the fund's portfolio will be leveraged if it exercises its right to delay payment on a redemption, and losses will result if the value of the fund's assets declines between the time a redemption request is deemed to be received by the fund and the time the fund liquidates assets to meet redemption requests.

Illiquidity risk. Some assets held by the fund may be or become impossible or difficult to sell and some assets that the fund wants to invest in may be impossible or difficult to purchase, particularly during times of market turmoil or due to adverse changes in the conditions of a particular issuer. These illiquid assets 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. As a general matter, dealers have been less willing to make markets in recent years. Federal banking regulations may also cause certain dealers to reduce their inventories of certain securities, which may further decrease the fund's ability to buy or sell such securities. During times of market turmoil, there have been, and may be, no buyers or sellers for securities in entire asset classes. If the fund is forced to sell an illiquid asset 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. The fund may not receive its proceeds from the sale of certain securities for an extended period (for example, several weeks or even longer).

Foreign investments and emerging markets risk. The fund's investments in securities of foreign issuers or issuers with significant exposure to foreign markets involve additional risk as compared to investments in U.S. securities or issuers with predominantly U.S. exposure, such as less liquid, less transparent, less regulated and more volatile markets. The value of the fund's investments may decline because of factors affecting the particular issuer as well as foreign markets and issuers generally, such as unfavorable or unsuccessful government actions, reduction of government or central bank support, inadequate accounting standards and auditing and financial recordkeeping requirements, lack of information, political, economic, financial or social instability, terrorism, armed conflicts and other geopolitical events, and the impact of tariffs and other restrictions on trade or economic sanctions. Geopolitical or other events such as nationalization or expropriation could even cause the loss of the fund's entire investment in one or more countries.

In addition, there may be significant obstacles to obtaining information necessary for investigations into or litigation against issuers located in or operating in certain foreign markets, particularly emerging market countries, and shareholders may have limited legal remedies.

The value of investments in securities denominated in foreign currencies increases or decreases as the rates of exchange between those currencies and the U.S. dollar change. Currency conversion costs and currency fluctuations could erase investment gains or add to investment losses. Currency exchange rates can be volatile, and are affected by factors such as general economic and political conditions, the actions of the U.S. and foreign governments or central banks, the imposition of currency controls and speculation. The fund may be unable or may choose not to hedge its foreign currency exposure.

Less developed markets are more likely to experience problems with the clearing and settling of trades and the holding of securities by local banks, agents and depositories. Settlement of trades in these markets can take longer than in other markets and the fund may not receive its proceeds from the sale of certain securities for an extended period (possibly several weeks or even longer).

The risks of foreign investments are heightened when investing in issuers in emerging market countries. Emerging market countries tend to have economic, political and legal systems that are less developed and are less stable than those of more developed countries. Their economies tend to be less diversified than those of more developed countries. They typically have fewer medical and economic resources than more developed countries, and thus they may be less able to control or mitigate the effects of a pandemic or a natural disaster. They are often particularly

sensitive to market movements because their market prices tend to reflect speculative expectations. Low trading volumes may result in a lack of liquidity and in extreme price volatility.

Sovereign debt risk. Sovereign government and supranational debt involve many of the risks of foreign and emerging markets investments as well as the risk of debt moratorium, repudiation or renegotiation, and the fund may be unable to enforce its rights against the issuers. Sovereign debt risk is increased for emerging market issuers.

Prepayment or call risk. Many issuers have a right to prepay their fixed income securities. Issuers may be more likely to prepay their securities if interest rates fall. If this happens, the fund may not benefit from the rise in the market price of the securities that normally accompanies a decline in interest rates, and will be forced to reinvest prepayment proceeds at a time when yields on securities available in the market are lower than the yield on prepaid securities. The fund may also lose any premium it paid to purchase the securities.

Extension risk. When interest rates rise, repayments of fixed income securities may occur more slowly than anticipated, extending the effective duration of these fixed income securities at below market interest rates and causing their market prices to decline more than they would have declined due to the rise in interest rates alone. This may cause the fund's share price to be more volatile.

Risk of investing in fewer issuers. To the extent the fund invests its assets in a small number of issuers, or in issuers in related businesses or that are subject to related operating risks, the fund will be more susceptible to negative events affecting those issuers.

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.

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. Ongoing or threatened armed conflicts throughout the world have caused and could continue to cause significant market disruptions and volatility. The hostilities and sanctions resulting from those hostilities have and could continue to have a significant impact on certain fund investments as well as fund performance and liquidity. 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.

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 been volatile and may increase in the future. 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.

The United States and other countries are periodically involved in disputes over trade and other matters, which may result in tariffs, investment restrictions and adverse impacts on affected companies and securities or the broader U.S. or global economies. For example, the United States has imposed tariffs and other trade barriers on Chinese exports, has restricted sales of certain categories of goods to China, and has established barriers to investments in China. Trade disputes may adversely affect the economies of the United States and its trading partners, as well as companies directly or indirectly affected and financial markets generally. The United States government has prohibited U.S. persons from investing in Chinese companies designated as related to the Chinese military. These and possible future restrictions could limit the fund's opportunities for investment and require the sale of securities at a loss or make them illiquid. Moreover, the Chinese government is involved in a longstanding dispute with Taiwan that has included threats of invasion. If the political climate between the United States and China does not improve or continues to deteriorate, if China were to attempt unification of Taiwan by force, or if other geopolitical conflicts develop or get worse, economies, markets and individual securities may be severely affected both regionally and globally, and the value of the fund's assets may go down.

Hedging risk. There can be no assurance that the fund will engage in hedging transactions at any given time, even under volatile market conditions, or that any hedging transactions the fund engages in will be successful. Hedging transactions involve costs and may reduce gains or result in losses.

Risks relating to inflation-indexed securities. The value of inflation-indexed fixed income securities generally fluctuates in response to changes in real interest rates, which are in turn tied to the relationship between nominal interest rates and the rate of inflation. If nominal interest rates increase at a faster rate than inflation, real interest rates might rise, leading to a decrease in value of inflation-indexed securities. The fund may also experience a loss on an

inflation-indexed security if there is deflation. If inflation is lower than expected during the period the fund holds an inflation-indexed security, the fund may earn less on the security than on a conventional bond.

Cash management and defensive investing risk. The value of the investments held by the fund for cash management or defensive investing purposes can fluctuate. Like other fixed income securities, they are subject to risk, including market, interest rate and credit risk. If the fund holds cash uninvested, the cash will be subject to the credit risk of the depository institution holding the cash and the fund will not earn income on the cash. If a significant amount of the fund's assets is used for cash management or defensive investing purposes, the fund will be less likely to achieve its investment objective. Defensive investing may not work as intended and the value of an investment in the fund may still decline.

Portfolio management risk. The value of your investment may decrease if the subadvisers' 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 models, tools and data used by the subadvisers. 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 subadvisers and could have an adverse effect on the value or performance of the fund.

Redemption risk. The fund may experience heavy redemptions that could cause the fund to liquidate its assets at inopportune times or unfavorable prices or increase or accelerate taxable gains or transaction costs and may negatively affect the fund's net asset value, performance, or ability to satisfy redemptions in a timely manner, which could cause the value of your investment to decline.

Cybersecurity risk. Like other funds and business enterprises, the fund, the manager, the subadvisers 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 subadvisers 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 subadvisers 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 subadvisers. 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 Class I shares. The table shows the average annual total returns of each class of the fund that has been in operation for at least one full calendar year and also compares the fund's performance with the average annual total returns of a broad measure of market performance and an additional index with characteristics relevant to the fund. 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, including its current net asset value, available at www.franklintempleton.com/prospectus (select fund and share class), or by calling the fund at 877-6LM-FUND/656-3863.

The fund's past performance (before and after taxes) is not necessarily an indication of how the fund will perform in the future.

Sales charges are not reflected in the accompanying bar chart, and if those charges were included, returns would be less than those shown.

Total returns (%)

Before taxes

Best Quarter (06/30/2020): 5.41 Worst Quarter (06/30/2022): (6.62)

No one index is representative of the fund's portfolio.

The after-tax returns are shown only for Class I shares, are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor's tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their fund shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns for classes other than Class I will vary from returns shown for Class I.

Important data provider notices and terms are available at www.franklintempletondatasources.com. Such information is subject to change.

Management

Investment manager: Franklin Templeton Fund Adviser, LLC ("FTFA")

Subadvisers: Western Asset Management Company, LLC ("Western Asset"), Western Asset Management Company Limited in London ("Western Asset London"), and Western Asset Management Company Pte. Ltd. in Singapore ("Western Asset Singapore"). References to the "subadviser" include each applicable subadviser.

Investment professionals: Primary responsibility for the day-to-day management of the fund lies with the following investment professionals. These investment professionals, all of whom are employed by Western Asset, work together with a broader investment management team.

Purchase and sale of fund shares

You may purchase, redeem or exchange shares of the fund each day the New York Stock Exchange is open, at the fund's net asset value determined after receipt of your request in good order, subject to any applicable sales charge.

The fund's initial and subsequent investment minimums generally are set forth in the accompanying table:

Your Service Agent may impose higher or lower investment minimums, or may impose no minimum investment requirement.

For more information about how to purchase, redeem or exchange shares, and to learn which classes of shares are available to you, you should contact your Service Agent, or, if you hold your shares or plan to purchase shares through the fund, you should contact the fund by phone at 877-6LM-FUND/656-3863, by regular mail at Legg Mason Funds, P.O. Box 33030, St. Petersburg, FL 33733-8030 or by express, certified or registered mail at Legg Mason Funds, 100 Fountain Parkway, St. Petersburg, FL 33716-1205.

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.

Franklin Distributors, LLC One Franklin Parkway San Mateo, CA 94403-1906 Investment Company Act file #811-06110 © 2026 Franklin Templeton. All rights reserved. 10% Total Recycled Fiber 00268194 90203-PSUM 05/26 Western Asset Inflation Indexed Plus Bond Fund