A long awaiting decision from the Supreme Court keeps subsidies alive for millions of Americans. At risk was the loss of subsidies to the Federal and Partnership exchanges due to one word in the law: "State". The law says that people applying on State exchanges could be eligible for tax subsidies from the Federal Gov't, It did not say subsidies are available to eligible individuals applying for coverage through an exchanges established by the Federal Government. However, most people agree the INTENT of the law was that everyone is eligible for a subsidy regardless of who set up the exchange. And the Supreme Court members agreed by a vote of 6 -3.
Some will remember, the law basically dictated to states that they MUST establish an exchange or one would be established for them. We know what happened next: about 30 states with Republican Governors said, "No thanks. You do it." A handful of states decided to partner with the Federal Gov't to set up their exchange, with the idea that they would eventually be running it down the road. (Illinois did just that and we now have a Partnership Exchange with the Federal Government). Keep in mind that setting up and establishing these exchanges was a costly proposition, even with money from the Fed. Gov't.
Read more on the decisions: http://www.nytimes.com/2015/06/26/us/obamacare-supreme-court.html?ref=health&_r=0