And in an additional unprecedented move from the central bank, interest rate decisions will now be tied to the unemployment rate and inflation.
About a half hour into the release, the Dow Jones Industrial Average staged a near 65-point rally - but then lost that gain and ended down nearly 3 points at 13,245.45.
Here's a breakdown of the FOMC meeting outcome.
Today's FOMC Meeting: QE4As expected, the FOMC meeting ended with a replacement for Operation Twist, the expiring program introduced in 2011 of swapping short-term Treasuries for longer dated ones. The goal of Operation Twist was to lower long-term interest rates to stimulate the U.S. economy.
The new asset purchase program is an extended arm of the Fed's familiar quantitative easing programs, and has thus been dubbed QE4.
Now with QE3 and QE4 together, the Fed will purchase a whopping $85 billion a month of Treasury securities, stacking the Fed's portfolio with government-backed investments for an extended period.
The buying spree will remain intact until the unemployment rate falls below 6.5% and inflation projections remain no more than half a percentage point above 2% for two years out.
The Fed also left interest rates at rock-bottom historic lows near zero, as was also expected.
While these moves were widely expected, what wasn't expected was the Fed's forward-looking guidance.