According to Megyn Kelly on Fox News, the AP is reporting that Gen. McChrystal has been relieved of command and General Petraeus will take over McChrystal's duties in Afghanistan.
President Obama will speak at 1:30 p.m.
Bill Kristol endorsed replacing McChrystal with Petraeus yesterday.
Update (1:45 p.m.): President Obama says that he has accepted General McChrystal's resignation. Watch video of the speech here, and find a transcript of Obama's speech here.