Apple have a livestream running now at the Steve Jobs Theatre. It's also being reported by The Verge.
https://www.apple.com/apple-events/livestream/
The video is stylized to look like a CRT television set, and has been switching between a handful of different angles of the theater. Presently, the theater’s screen has a classic Apple screensaver on the screen, although some Twitter users have spotted some other things pop up on the screen, like a screenshot of an incoming call from Captain America himself, Chris Evans. It seems likely that that’s a nod to the shows that Apple is expected to unveil, as Evans is starring in one of them, an eight-episode thriller series called Defending Jacob.
Another Twitter user pointed out that this isn’t likely a live stream of the theater, noting that the company is probably in the midst of rehearsing for tomorrow’s event.