That's what it seems like. Based on a picture from zombie reddit:
Here's the link: mbta.com/lasttrip
And from that link:
Here's the link: mbta.com/lasttrip
And from that link:
Most trains run between about 5 AM and 1 AM, and some lines have service as late at 1:50 AM.
To make the final train connections of the night, get to one of these downtown stations by 12:35 AM:
Service runs more frequently during rush hour, between 6:30 AM – 9 AM and 3:30 PM – 6:30 PM on weekdays.
See all subway schedules