SEC Form 424B3 filed by Eaton Vance Senior Income Trust

EATON VANCE SENIOR INCOME TRUST

Supplement to Prospectus and Statement of Additional Information dated August 25, 2022

as may be supplemented and/or revised from time to time

1. The following replaces the fifth paragraph under “The Adviser” in “Management of the Trust” in the Trust’s Prospectus:

Peter Campo, Catherine C. McDermott and Daniel P. McElaney are the portfolio managers of the Trust. Mr. Campo and Ms. McDermott are Managing Directors of Morgan Stanley and Vice Presidents of Eaton Vance. Mr. McElaney is an Executive Director of Morgan Stanley and a Vice President of Eaton Vance. Ms. McDermott and Mr. McElaney have managed the Trust since March 2019, and Mr. Campo has managed the Trust since June 12, 2025. Ms. McDermott and Mr. McElaney have been employees of the Morgan Stanley organization for more than five years and manage other Eaton Vance funds. Mr. Campo has been an employee of the Morgan Stanley organization since April 2025 and manages other Eaton Vance funds. Prior to joining Morgan Stanley, Mr. Campo worked at Goldman Sachs as Global Co-Head of High Yield & Bank Loan Credit since March 2018. Prior to joining Goldman Sachs, Mr. Campo served for more than 15 years as a Portfolio Manager and senior credit analyst on the Floating-Rate Loan team at Eaton Vance.

2. The following replaces the tables under “Portfolio Managers.” in “Investment Advisory and Other Services” in the Trust’s SAI: