Tens of thousands of low-income Berkshires residents face changes in the MassHealth program, part of the state's first Medicaid overhaul in two decades.

The Berkshire Eagle reports for patients, it's time to act on all those letters over the past months — and it might mean selecting a new primary care physician.

For doctors, it's a large-scale rollout of the system known as "accountable care." In that, they serve as gatekeepers to improve care and contain costs.

For Berkshire Health Systems and Community Health Programs, it's the dawn of a partnership in which they take on financial risks usually borne by insurers.

And for Fallon Health, Thursday marked the start of a new business chapter in Berkshire County.

The new Fallon network will care for all participating Berkshire County residents.

The MassHealth revamp, required through a 2016 agreement with the federal government, is designed in part to stabilize finances of the program, which serves 1.9 million residents.

Roughly 650,000 current MassHealth members will see no change, according to the state.

In Berkshire County, about 40,000 people are enrolled with MassHealth, the program says. The new network will only be used by MassHealth members younger than 65 for whom MassHealth is their primary insurance. People eligible for Medicare will not take part.