From the Boston Consulate page:
IMPORTANT INFORMATION
END OF VISA EXEMPTION FOR U.S. CITIZENS
Effective October 1st, 2023, U.S. citizens will need a visa to travel to Brazil on tourism or business. Applications are not open yet. Updates will be posted here timely.
If you travel to Brazil before October 1st, 2023, YOU DO NOT NEED A VISA, even if you leave the country after this date.