Of the estimated 12-13 million people who, in the end, appear to have enrolled in ACA exchange policies for this year, around 10-11 million of them are receiving federal tax credits, either as a monthly subsidy towards their premiums or as a "lump sum" tax rebate the following spring.
Either way, exchange enrollees will have to include two important new forms when filing their federal income taxes this year:
I've mused before about how Avik Roy has a tendency to write lengthy screeds which breathlessly report developments which seem, to him, to be shocking revelations which will no doubt blow the lid off of some sort of nefarious actions on the part of President Obama, the HHS Dept. or Democrats in general...but which, when looked at by a rational person, tend to be fairly innocuous developments which were either already known, patently obvious and/or pretty much non-events in the scheme of things.
For instance, check out this blockbuster from back in March, regarding the HHS Dept's contingency plan in the event that the Obama administration had lost the King v. Burwell case at the Supreme Court (spoiler: they ended up winning):