It sounds like the briefings are today. I don't expect any news today.
Just like with the AirPods Pro. The private meetings were held the day before, and then...bamb! The next day, the Apple's newsroom website got refreshed and the AirPods were on sale!
I think the MBP is going to take a similar route to the announcement and then release, albeit, not being on store shelves immediately, but being able to purchase immediately.