Musk has previously hinted that the event may show the completed prototype before its first suborbital flight. There is also an opportunity for SpaceX to reduce the deadline for this flight, which could happen as early as October. Other updates may include design changes and revisions to the long-term schedule. Many details are not set in stone and you are likely to see significant changes.
As it stands now, the Starship prototype will have three Raptor engines (six in the ready version) and should reach a height of 1
Update 9/28 6PM ET: SpaceX is a revamped update to "no earlier than" 9PM east of the original 8PM due to time. We updated the story accordingly.