Share class (Symbol): A (STXAX), C (SMHLX), FI ( — ), I (LMHIX), IS (LMHSX)

WESTERN ASSET

MUNICIPAL HIGH INCOME 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 and shareholder reports, online at www.franklintempleton.com/mutualfundsliterature. 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 prospectus@franklintempleton.com, or from your financial intermediary. The fund’s Prospectus and statement of additional information, each dated December  1, 2024 (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 July 31, 2024, are incorporated by reference into this Summary Prospectus.

Investment objective

The fund seeks to maximize current income exempt from regular federal income tax.

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 26 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 95 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 20% of the average value of its portfolio.

Principal investment strategies

Under normal circumstances, the fund invests at least 80% of its assets in “municipal securities.” Municipal securities are securities and other investments with similar economic characteristics, the interest on which is exempt from regular federal income tax. The fund’s 80% policy may not be changed without a shareholder vote. Interest on municipal securities may be subject to the federal alternative minimum tax.

Municipal securities include debt obligations issued by any of the 50 states and certain other municipal issuers and their political subdivisions, agencies and public authorities, certain other governmental issuers (such as Puerto Rico, the U.S. Virgin Islands and Guam) and other qualifying issuers. These securities include participation or other interests in municipal securities issued or backed by banks, insurance companies and other financial institutions.

Some municipal securities, such as general obligation issues, are backed by the issuer’s taxing authority, while other municipal securities, such as revenue issues, are backed only by revenues from certain facilities or other sources and not by the issuer itself.

Under normal market conditions, the fund will invest primarily in municipal securities rated at the time of purchase in the lowest investment grade categories (that is, securities rated in the Baa/BBB categories) or rated below investment grade (that is, securities rated below the Baa/BBB categories) or, if unrated or deemed to be unrated by the subadviser, determined by the subadviser to be of comparable credit quality. However, the fund is permitted to invest in securities rated in any investment category. Below investment grade securities are commonly referred to as “high yield” or “junk” bonds.

The fund focuses on intermediate- and long-term municipal securities.

Under normal circumstances, the fund may invest up to 20% of its assets in fixed income securities and other investments whose interest may be subject to federal income tax, although for temporary or defensive purposes, the fund may invest an unlimited amount in such securities.

Instead of, and/or in addition to, investing directly in particular securities, the fund may use instruments such as derivatives, including options, futures contracts and inverse floating rate instruments issued in tender option bond transactions, and other synthetic instruments that are intended to provide economic exposure to the securities or the issuer or to be used as a hedging technique. The fund may use one or more types of these instruments without limit, subject to applicable regulatory requirements. These instruments are taken into account when determining compliance with the fund’s 80% policy. For additional information regarding derivatives, see “More on the fund’s investment strategies, investments and risks—Derivatives” in the Prospectus.

The fund may also engage in a variety of transactions using derivatives in order to change the investment characteristics of its portfolio (such as shortening or lengthening duration) and for other purposes. The fund may leverage its assets by investing proceeds received through tender option bond transactions, which is considered a form of borrowing. See “More on the fund’s investment strategies, investments and risks—Tender option bonds” in the Prospectus.

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, including by taking action intended to increase certain interest rates. 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.

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 armed conflicts between Russia and Ukraine in Europe and among Israel, Hamas and other militant groups in the Middle East 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.

Inflation risk. Inflation risk is the risk that the value of assets or income from investments will be worth less in the future as prices go up and the purchasing power of money goes down. The market prices of debt securities generally fall as inflation increases because the purchasing power of the principal and income is expected to be less when paid. Inflation often is accompanied or followed by a recession, or period of decline in economic activity, which may include job loss and other hardships and may cause the value of securities to go down generally.

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, 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, including the proportion of income consisting of exempt interest dividends, as applicable. The U.S. government and foreign 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.

Tender option bond risk. Tender option bond (“TOB”) transactions expose the fund to leverage and credit risk, and generally involve greater risk than direct investments in fixed rate municipal bonds, including the risk of loss of principal. The interest payments that the fund would typically receive in connection with a TOB transaction (“inverse floaters”) vary inversely with short-term interest rates and will be reduced (and potentially eliminated) when short-term interest rates increase. In addition, the fund will be subject to leverage risk to the extent that the fund uses the proceeds that it receives from a TOB transaction to invest in other securities. The fund’s investment in a TOB will generally underperform the market for fixed rate municipal securities when interest rates rise. The value and market for such inverse floaters can be volatile and can have limited liquidity. Investments in inverse floaters issued in TOB transactions are derivative instruments and, therefore, are also subject to the risks generally applicable to investments in derivatives.

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).

Tax risk. The income on the fund’s municipal securities could become subject to U.S. federal income tax due to noncompliant conduct by issuers, unfavorable legislation or litigation or adverse interpretations by regulatory authorities. All or a portion of the fund’s dividends that are exempt from regular U.S. federal income tax may nevertheless be taken into account for purposes of the U.S. federal alternative minimum tax.

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, particularly asset- and mortgage- backed 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.

Risks relating to investments in municipal securities. Municipal issuers may be adversely affected by rising health care costs, increasing unfunded pension liabilities, and by the phasing out of federal programs providing financial support. Unfavorable conditions and developments relating to projects financed with municipal securities can result in lower revenues to issuers of municipal securities, potentially resulting in defaults. The value of municipal securities can also be adversely affected by changes in the financial condition of one or more individual municipal issuers or insurers of municipal issuers, regulatory and political developments, tax law changes or other legislative actions, and by uncertainties and public perceptions concerning these and other factors. In the past, a number of municipal issuers defaulted on obligations, were downgraded or commenced insolvency proceedings. Financial difficulties of municipal issuers may experience a resurgence, particularly in the event of economic or market turmoil or a recession.

Investing in ETFs risk. Unlike shares of typical mutual funds or unit investment trusts, shares of exchange-traded funds (“ETFs”) are traded on an exchange and may trade throughout a trading day. ETFs are bought and sold based on market values and not at net asset value, and therefore may trade at either a premium or discount to net asset value and may experience volatility in certain market conditions. The fund will pay brokerage commissions in connection with the purchase and sales of shares of ETFs. In addition, the fund will indirectly bear its pro rata share of fees and expenses incurred by an ETF in which it invests, including advisory fees. These expenses are in addition to management fees and other expenses that the fund bears directly in connection with its own operations. Certain ETFs are also subject to portfolio management risk. Investments in ETFs are subject to the risk that the listing exchange may halt trading of an ETF’s shares, in which case the fund would be unable to sell its ETF shares unless and until trading is resumed.

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.

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 models, 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.

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 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 Class A 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. 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/mutualfunds (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.

Best Quarter (12/31/2023): 8.50 Worst Quarter (03/31/2022): (5.81)

The year-to-date return as of the most recent calendar quarter, which ended September 30, 2024, was 4.88

The after-tax returns are shown only for Class A shares, are calculated using the historical highest individual 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. After-tax returns for classes other than Class A will vary from returns shown for Class A. Returns after taxes on distributions and sale of fund shares are higher than returns before taxes for certain periods shown because they reflect the tax benefit of capital losses realized on the redemption of fund shares.

Management

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

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

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 intends to distribute income that is generally exempt from regular U.S. federal income tax. A portion of the fund’s distributions may be subject to such tax and/or to the U.S. federal alternative minimum tax.

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.

Investment Company Act file #811-04254

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