Media event set for September 9, launch likely ~10 days later.
WWDC 2013 Keynote Live Video Stream Available via Apple's Website
The teaser text on Apple's main page reads: "View streaming video from today's big event starting at 10 a.m. PDT."
The video stream requires Safari 4 or later on a minimum of Mac OS X Snow Leopard, or iOS 4.2 or later for those accessing the stream from a mobile device. Streaming via Apple TV requires second- or third-generation Apple TV with a minimum of software version 5.0.2.
Apple's event kicks off at 10:00 AM Pacific Time, and MacRumors will have full coverage of the event's announcements.
Update 5:34 AM: Apple has also issued a press release announcing the live video stream.