In a 6-3 decision, the Supreme Court affirmed the Fourth Circuit decision in King v. Burwell. The majority opinion noted that "Congress passed the Affordable Care Act to improve health insurance markets, not to destroy them." You can read the opinion, authored by Chief Justice Roberts, at this link.
Immediate coverage is available here:
Modern Healthcare: Supreme Court upholds subsidies in King v. Burwell
Wall Street Journal: Supreme Court Upholds Obama’s Health-Law Subsidies
New York Times: Supreme Court Allows Nationwide Health Care Subsidies