Prospectus by Investment Company - Form 497

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THORNBURG INVESTMENT TRUST SUPPLEMENT

Dated November 8, 2024

to the

THORNBURG FUNDS PROSPECTUS

applicable to Class A, C, C2, D and I shares
dated February 1, 2024, as supplemented March 13, April 19, August 16, August 21,
and September 30, 2024
(the "Retail Prospectus")

Effective November 8, 2024, the following information replaces the sub-section relating to Ameriprise Financial in the "Appendix A - Sales Charge Waivers Offered by Financial Intermediaries" section on page 214 of the Retail Prospectus:

Ameriprise Financial

Front-end sales charge reductions on Class A shares purchased through Ameriprise Financial

Shareholders purchasing Class A shares of a Fund through an Ameriprise Financial platform or account are eligible only for the following sales charge reductions, which may differ from those disclosed elsewhere in this prospectus or the SAI. Such shareholders can reduce their initial sales charge on the purchase of Class A shares as follows:

•Transaction size breakpoints, as described in this prospectus or the SAI.

•Rights of accumulation (ROA), as described in this prospectus or the SAI.

•Letter of intent, as described in this prospectus or the SAI.

Front-end sales charge waivers on Class A shares purchased through Ameriprise Financial

Shareholders purchasing Class A shares of a Fund through an Ameriprise Financial platform or account are eligible only for the following sales charge waivers, which may differ from those disclosed elsewhere in this prospectus or the SAI. Such shareholders may purchase Class A shares at NAV without payment of a sales charge as follows:

•shares purchased by employer-sponsored retirement plans (e.g., 401(k) plans, 457 plans, employer- sponsored 403(b) plans, profit sharing and money purchase pension plans and defined benefit plans). For purposes of this provision, employer-sponsored retirement plans do not include SEP IRAs, Simple IRAs or SAR-SEPs.

•shares purchased through reinvestment of capital gains and dividend reinvestment when purchasing shares of the same Fund (but not any other Fund within the same Fund family).

•shares exchanged from Class C shares of the same Fund in the month of or following the seven-year anniversary of the purchase date. To the extent that this prospectus elsewhere provides for a waiver with respect to such shares following a shorter holding period, that waiver will apply to exchanges following such shorter period. To the extent that this prospectus elsewhere provides for a waiver with respect to exchanges of Class C shares for load waived shares, that waiver will also apply to such exchanges.

•shares purchased by employees and registered representatives of Ameriprise Financial or its affiliates and their immediate family members.

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•shares purchased by or through qualified accounts (including IRAs, Coverdell Education Savings Accounts, 401(k)s, 403(b) TSCAs subject to ERISA and defined benefit plans) that are held by a covered family member, defined as an Ameriprise Financial advisor and/or the advisor's spouse, advisor's lineal ascendant (mother, father, grandmother, grandfather, great grandmother, great grandfather), advisor's lineal descendant (son, step-son, daughter, step-daughter, grandson, granddaughter, great grandson, great granddaughter) or any spouse of a covered family member who is a lineal descendant.

•shares purchased from the proceeds of redemptions within the same Fund family, provided (1) the repurchase occurs within 90 days following the redemption, (2) the redemption and purchase occur in the same account, and (3) redeemed shares were subject to a front-end or deferred sales load (i.e. Rights of Reinstatement).

CDSC waivers on Class A and C shares purchased through Ameriprise Financial

Fund shares purchased through an Ameriprise Financial platform or account are eligible only for the following CDSC waivers, which may differ from those disclosed elsewhere in this prospectus or the SAI:

•redemptions due to death or disability of the shareholder.

•shares sold as part of a systematic withdrawal plan as described in this prospectus or the SAI.

•redemptions made in connection with a return of excess contributions from an IRA account.

•shares purchased through a Right of Reinstatement (as defined above).

•redemptions made as part of a required minimum distribution for IRA and retirement accounts pursuant to the Internal Revenue Code.

PLEASE KEEP THIS SUPPLEMENT FOR FUTURE REFERENCE

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