New York has added 1.1 million people to Medicaid since the state health exchange opened last year in the national effort to connect the uninsured with low-cost coverage.
More than 6.2 million New Yorkers are now enrolled, almost one-third of its 19 million people.
The exchange, designed to connect uninsured New Yorkers with commercial policies, had the effect of bringing a larger number of low-income residents to the government-funded program.
Elisabeth Benjamin, vice president for health initiatives at the Community Service Society of New York, said the expansion has succeeded in the goal of reducing the state's uninsured, which was estimated at 2.7 million people.
"It's working," she said.
New census data in September should show how many uninsured are left, Benjamin said.
Enrollment under the Affordable Care Act has surged beyond expectations in some states, raising concerns about costs straining budgets. At least seven states have increased their cost estimates for 2017, according to an Associated Press analysis.
Medicaid in New York costs about $63.5 billion this year, almost half the state budget. That's up from $52.1 billion five years ago.
However, the state's $22.5 billion share this year is flatter, up from $21.3 billion five years ago, according to budget officials.