For the Fund’s Prospectus or SAI, visit www.thornburg.com/download

Thornburg Core Plus Bond FundSummary Prospectus​

Before you invest, you may want to review the Fund’s Prospectus and Statement of Additional Information (SAI), which contain more information about the Fund and its risks. You can find the Fund’s Prospectus, SAI and other information about the Fund online at www.thornburg.com/download. You can also get this information at no cost by calling 800.847.0200 or by sending an e-mail request to info@thornburg.com. The current Prospectus and SAI, dated February 1, 2024, are incorporated by reference into this Summary Prospectus.

Investment Goal

The Fund seeks to maximize total return, consistent with the long-term preservation of capital.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold 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.

Shareholder Fees

(fees paid directly from your investment)

Annual Fund Operating Expenses

(expenses that you pay each year as a percentage of the value of your investment)

(1)Other expenses in the table are estimated for the current fiscal year before expense reimbursements.

(2)Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4, Class R5, and Class R6 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.00%, 0.75%, 0.50%, and 0.49%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2025, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.

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 that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year) your costs would be:

For the Fund’s Prospectus or SAI, visit www.thornburg.com/download

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 Fund 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. Because the Fund commenced investment operations on October 2, 2023, information about the Fund’s portfolio turnover rate is not currently available.

Principal Investment Strategies

Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio in pursuing the Fund’s investment goal. Under normal conditions, the Fund invests at least 80% of its net assets in debt obligations. The Fund may invest up to 25% of its net assets in debt obligations which, at the time of purchase, are rated by a nationally recognized statistical rating organization as below investment grade (sometimes called “junk” bonds or “high yield” bonds) or, if unrated, are issued by obligors which Thornburg determines to have comparable below investment grade obligations outstanding or to be comparable to obligors with outstanding below investment grade obligations. The Fund may not, at the time of purchase, invest more than 25% of its net assets in debt obligations denominated in non-U.S. currencies, but this limitation does not apply to debt obligations issued by foreign issuers and denominated in U.S. dollars. Additionally, the Fund may not, at the time of purchase, invest more than 15% of its net assets in debt obligations issued by issuers in emerging markets, also known as developing countries. As used herein, the term “net assets” includes the amount of any borrowings made by the Fund for investment purposes.

There is no limitation on the duration or maturity of any specific debt obligation the Fund may purchase. The Fund will, however, generally seek to maintain a portfolio of investments with a dollar-weighted average duration that falls within two years of the dollar-weighted average duration of the Fund’s benchmark index, the Bloomberg U.S. Aggregate Bond Index. Duration is a measure of estimated sensitivity to interest rate changes, and a debt obligation or a portfolio of obligations with a higher duration will typically be more sensitive to interest rate changes than an obligation or a portfolio with a lower duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example, an obligation with a duration of 0.5 would be expected to change in price by approximately 0.5% in response to a 1% change in interest rates.

While the Fund may invest in debt obligations of any type, the Fund will typically invest in the following types of debt obligations:

•corporate debt obligations from domestic and foreign issuers of any market capitalization;

•obligations issued or guaranteed by U.S. and non-U.S. governments and their agencies or instrumentalities; and

•mortgage-backed and asset-backed securities, including residential or commercial mortgage-backed securities, or collateralized mortgage obligations, issued by agencies of the U.S. government or issued by private entities.

Each of the Fund’s investments is determined by individual issuer and industry analysis, including Thornburg’s evaluation of domestic and international economic developments, outlooks for securities markets, interest rates and inflation, and the supply and demand for debt obligations.

The Fund may also invest in futures contracts, options, swaps, and forward contracts to hedge against the decline in the value of certain of the Fund’s investments, to manage portfolio duration, or to enhance the Fund’s investment returns.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  Because the Fund seeks to maximize total return while also preserving capital, the Fund may not always obtain the highest yields available.

The Fund’s policy of investing at least 80% of its net assets in debt obligations may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders.

Principal Investment Risks

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. If your sole objective is preservation of capital, then the Fund may not be suitable for you because the Fund’s share value will fluctuate, including as interest rates change. Investors whose sole objective is preservation of capital may wish to consider a high-quality money market fund. The following is a summary of the principal risks of investing in the Fund. The risks are presented in alphabetical order to facilitate readability, and their order does not imply that the realization of one risk is more likely to occur or have a greater adverse impact than another risk. The relative significance of each risk below may change over time.

Credit Risk – If obligations held by the Fund are downgraded by ratings agencies or go into default, or if management action, legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Because the ability of an issuer of a lower-rated or unrated obligation to pay principal and interest when due is typically less certain than for an issuer of a higher-rated obligation, lower-rated and unrated obligations are generally more vulnerable than higher- rated obligations to default, to ratings downgrades, and to liquidity risk. Debt obligations backed by so-called “subprime” mortgages may also be subject to a greater risk of default or downgrade. Debt obligations issued by the U.S. government or its agencies, instrumentalities and government sponsored enterprises are also subject to credit risk. Securities backed by the full faith and credit of the U.S. government, such as U.S. Treasury obligations, are commonly regarded as having small exposure to credit risk. Obligations of certain U.S. agencies, instrumentalities and enterprises (sometimes referred to as “agency obligations”) are not direct obligations of the U.S. government, may not be backed by the full faith and credit of the U.S. government, and may have a greater exposure to credit risk.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants, or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

For the Fund’s Prospectus or SAI, visit www.thornburg.com/download

Derivatives Risk – The Fund’s investments in futures contracts, options, swaps, forward contracts, and other derivative instruments involve the risks associated with the securities or other assets underlying those derivatives, and also may involve risks different or greater than the risks affecting the underlying assets, including the inability or unwillingness of the other party to a derivative to perform its obligations to the Fund, the Fund’s inability or delays in selling or closing positions in derivatives, and difficulties in valuing derivatives.

Emerging Markets Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” below) may be more pronounced for investments in emerging markets, also known as developing countries, because the economies of those markets are usually less diversified, communications, transportation and economic infrastructures are less developed, and emerging markets ordinarily have less established legal, political, business and social frameworks. At times the prices of debt obligations of an issuer in an emerging market may be extremely volatile. An issuer in a developed country may be similarly affected by these emerging markets risks to the extent that the issuer conducts its business in emerging markets.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Foreign Investment Risk – Investments in the debt obligations of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection. In addition, some foreign government debt obligations may be subject to default, delays in payment, adverse legislation or government action, or could be downgraded by ratings agencies.

High Yield Risk – Debt obligations that are rated below investment grade and unrated obligations of similar credit quality (commonly referred to as “junk” or “high yield” bonds) may have a substantial risk of loss. These obligations are generally considered to be speculative with respect to the issuer’s ability to pay interest and principal when due. These obligations may be subject to greater price volatility than investment grade obligations, and their prices may decline significantly in periods of general economic difficulty or in response to adverse publicity, changes in investor perceptions or other factors. These obligations may also be subject to greater liquidity risk.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. This effect is also typically more pronounced for mortgage- and other asset-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends may decline.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices. The market for lower-rated and unrated debt obligations (including particularly “junk” or “high yield” bonds) and debt obligations backed by so-called “subprime” mortgages may be less liquid than the market for other obligations, making it difficult for the Fund to value its investment in a lower-rated or unrated obligation or to sell the investment in a timely manner or at an acceptable price.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. This effect is typically more pronounced for lower-rated and unrated debt obligations (including particularly “junk” or “high yield” bonds), the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic, and legal developments, and developments affecting specific issuers.

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed and asset-backed securities.

Redemption Risk – If a significant percentage of the Fund’s shares is owned or controlled by a single shareholder, the Fund is subject to the risk that a redemption by that shareholder of all or a large portion of its shares may require the Fund to sell securities at less than desired prices, and the Fund’s remaining shareholders may also incur additional transaction costs or adverse tax consequences from such trading activity.

Risks Affecting Specific Issuers – The value of a debt obligation may decline in response to developments affecting the specific issuer of the obligation or security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Small and Mid-Cap Company Risk – Debt obligations of small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility, and possible difficulties in valuing or selling these investments.

Structured Products Risk – Investments in securities that are backed by, or represent interests in, an underlying pool of securities or other assets, including investments in mortgage- and asset-backed securities and in collateralized mortgage obligations, involve the risks associated with the underlying assets (e.g., the risk of default by mortgagors whose mortgages are included in a mortgage-backed security or collateralized mortgage obligation), and may also involve different or greater risks, including the risk that distributions from the underlying assets will be inadequate to make interest or other payments to the Fund, the risk that the issuer of the securities will fail to administer the underlying assets properly or become insolvent, and the risk that the securities will be less liquid than other Fund investments.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears below beginning on page 66.

Past Performance of the Fund

No performance information is presented because the Fund has less than one calendar year of performance as of the date of this Prospectus.

For the Fund’s Prospectus or SAI, visit www.thornburg.com/download

2/1/24
TH6065

Management

Investment Advisor: Thornburg Investment Management, Inc.

Portfolio Managers:

Lon Erickson, cfa, a managing director of Thornburg, has been one of the persons jointly and primarily responsible for the day-to-day management of the Fund since its inception in 2023.

Christian Hoffmann, cfa, a managing director of Thornburg, has been one of the persons jointly and primarily responsible for the day-to-day management of the Fund since its inception in 2023.

Jeff Klingelhofer, cfa, a managing director and co-head of investments of Thornburg, has been one of the persons jointly and primarily responsible for the day-to-day management of the Fund since its inception in 2023.

Purchase and Sale of Fund Shares

Employer-sponsored retirement plans wishing to make shares of the Fund available to plan participants should contact a financial intermediary authorized to sell shares of the Fund. As a participant in an employer-sponsored retirement plan that makes Fund shares available, you may add shares to your account by contacting your plan administrator. Although the Fund does not currently impose any investment minimums on the purchase of shares through an employer-sponsored retirement plan, the plan itself may establish such minimums. Contact your plan administrator for more information.

Please contact your retirement plan administrator if you wish to sell your shares. Your plan administrator will conduct the transaction for you, or provide you with the means to conduct the transaction yourself.

Tax Information

Fund distributions to qualified retirement plan accounts, and transactions in Fund shares by those accounts, are not generally subject to current federal income tax under existing federal law. Please see “Taxes” on page 89 of the Prospectus for additional information. Purchasers are cautioned to seek the advice of their own advisors about the tax consequences of contributions to plan accounts and distributions from plan accounts.

Payments to Broker-Dealers and Other Financial Intermediaries

If you purchase shares of the Fund through a broker-dealer or other financial intermediary (such as a bank), the Fund, its investment advisor and/or its distributor may pay the intermediary for the sale of Fund shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary’s website for more information.