Prices and other information about next year’s Affordable Care Act plans in the 12 states, as well as the District of Columbia, that have their own marketplaces will be announced by those places. In all, 10.6 million people had health plans through the federal and state marketplace plans as of March, the last time the Trump administration released enrollment data.

As the market stabilizes, the health law is coming to serve almost exclusively the struggling families and individuals who qualify for federally subsidized coverage. In a call with reporters on Monday, Seema Verma, the administrator of the Centers for Medicare and Medicaid Services, which runs the online marketplace, said that from 2016 to 2018, the number of health-law enrollees who did not qualify for premium subsidies dropped by 2.5 million people, or 40 percent.

“It was inevitable that Obamacare’s affordability crisis would eventually increase the number of uninsured,” Ms. Verma said, pointing to new census data showing a rise in the number of higher-income Americans without insurance.

In 2018, 8.5 percent of the population lacked health insurance, according to the Census Bureau, up from 7.9 percent in 2017. But that was driven in large part by a decline in the number of children insured under government programs like Medicaid and the Children’s Health Insurance Program. The administration has taken steps to limit Medicaid eligibility for immigrants, and has supported efforts by some states to impose work requirements on Medicaid recipients.

[Read what is driving the rise in rates of uninsured children.]

The administration has also all but eliminated funding to promote enrollment under the law, through advertising and “navigators,” who once helped people sign up.

Ms. Verma and Mr. Azar praised Congress for zeroing out the tax penalty that the law imposed on people who go without health insurance; it did so as part of the 2017 tax overhaul. They also praised new rules pressed by Mr. Trump that encourage the sale of less expensive coverage that does not provide the comprehensive benefits required by the health law. Both moves, Ms. Verma said, elicited “a kneejerk chorus of dire predictions” that had not come to fruition.