The Trump administration on Thursday released a final rule that slashes the open enrollment period for Affordable Care Act coverage in 2018 in half, among other changes, in its first major regulatory change affecting Obamacare.

The regulation, which aims to stabilize the ACA exchanges, could have a significant impact on the marketplace, but it leaves unanswered insurers’ biggest question: whether the government would continue funding the ACA’s cost-sharing subsidies, which help lower-income consumers afford out-of-pocket health costs.

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