...at least for a little bit.
St. Pierre told Joe Rogan in the cage that he has "a lot of things going on in his life" and that he "needs to hang up the gloves." St. Pierre added "I have to go away for a little bit." While it didn't sound like it was guaranteed to be a long-term retirement, it does sound like it will be at least a little while before he steps back into the Octagon.
It's worth remembering all the great fighters who have stepped away during what seemed like the prime of their career and returned after a year or two (Floyd Mayweather Jr. springs to mind).
And Ariel Helwani suggested that that is exactly what might happen:
What I was told was GSP wanted to retire with a win and walk away for 1 year or so. Maybe 2. Hopefully we can find out more.— Ariel Helwani (@arielhelwani) November 17, 2013
This does leave Hendricks, who most seem to consider to have been "robbed" without any sort of path to avenging the loss, but one would have to assume he'll be put into any sort of interim or full title fight in the near future.
We will have much, much more on this development as well as the rest of the fallout from UFC 167 over the coming hours and days.