Thanks to Danny Simmons‘ comment below clarifying that the provides that support EF3.5 will still work for EF4 "just without new provider affecting features like model first."
As far as I can tell, and confirmed by Fabio Pandolfo (@fabiopand on twitter) who is also on the hunt, DevArt’s Oracle provider might be the only 3rd party provider that is currently somewhat supporting EF4, though they are publically claiming Beta 2 support, not VS2010RC. If you read this thread on their forums, you’ll see why I qualify that with “somewhat”.
If you have any clues about the status of other EF providers and their support for EF4, leave a comment here.
Sign up for my newsletter so you don't miss my conference & Pluralsight course announcements!