At 1pm PT
Sony is teasing a stream of something on the Twitch PlayStation page. Their blog post says that "the revolution will be televised..." and suggests that you might want to change your evening plans to see what they have in store.
While they never come right out and say what we'll be seeing at 1:00 PM PT today, the background of their teaser shows the logo for upcoming PS4 game The Order 1886. They do say that we'll see a sneak peek at new gameplay.