Both, they supplement the "wild" with hatchery fish every year or so. I imagine that they would also have "wild or spawned fish also although maybe rare I am no biologist but I am sure some of those fish spawn and the young survive.
FYI I have heard reports way back of them running all the way up to rt 202 in the quabbin area on the west branch of the I think swift river. I made it out there one year to look but failed to hook a single fish or see anything. Lots and Lots of little places like that if you want to hike in the quabbin to fly fish those small brooks. there are dozens. Some hold wild brook trout, But its a very tight lipped thing aside from me posting on the internet.