Rome's public transport system will follow a reduced schedule during the main holidays over the 2021 Christmas season.

24 Dec. Christmas Eve. All metro, buses, trams and regional train services and Roma TPL buses run until 21.00. Night buses run as normal from 23.30.
25 Dec. Christmas Day. ATAC buses, metro, trams and Roma TPL run from 08.30-13.00 and 16.30-21.00.
26 Dec. St Stephen's Day. Service runs according to normal Sunday/festivo timetable.
31 Dec. New Year's Eve. All metro services run until 02.30 at night (early hours of 1 Jan), with night buses running from 21.00 to 02.30.
1 Jan 2022. New Year's Day. Entire ATAC and Roma TPL network resumes at 08.00 and follows normal festivo timetable.
For full transport details see ATAC website.