The Rails 8 release notes are here: Ruby on Rails 8.0 Release Notes — Ruby on Rails Guides
Note that there are no mentions whatsoever of new features or changes. Compared to previous releases, there’s nothing in them but deprecations / removals.
I’m assuming something went wrong somewhere and the guide somehow didn’t get updated?
There is also no information regarding upgrading: Upgrading Ruby on Rails — Ruby on Rails Guides
Your assumptions are wrong 
. Rails 8 is pretty much an update of the defaults, the environment and the infrastructure/infrastructual defaults needed. Its tagged as being (“again”) a straight-forward, battle-tested, batteries-included single-person web-application-framework (e.g. without needing to install, run and maintain a redis server instance, like you would have by default in production Rails 7).
I don’t know why those release notes in the Rails Guides are so limited. It does seem incomplete. Here’s a better post from the Rails blog:
At the very least there should be some indication of the updates that are mentioned in the post linked below. The changelog seems to indicate that nothing at all changed in Rails 8, which is definitely not the case.
The switch from Sprockets to Propshaft by default seems to be a huge one in and of itself.
Thank you for sharing this information…