Via Hoodline, a news network reporting on local events in San Francisco:
Today a trusted source confirmed to us that yes, the activity at Bill Graham is indeed preparing for an Apple event.
Our source, who wished to remain anonymous due to the extreme privacy surrounding the event, has shown us documentation from event logistics indicating that Apple is renting the building through September 12th. This timing is consistent with what we were told by a security guard on Monday.
Last year's September location, the Flint Center, has a seating capacity of 2400 and was widely touted as a “big” event. The Bill Graham Civic Auditorium seats 7000.