The Entity Framework is now being developed under an open-source license and EF6 and above will not be shipped as part of the .NET Framework. This has many advantages but also requires that EF providers be rebuilt against the EF6 assemblies. This means that EF providers for EF5 and below will not work with EF6 until they have been rebuilt.
Providers we are aware of that have been rebuilt for EF6 include:
Note that inclusion in this list does not indicate the level of functionality or support for a given provider, only that a build for EF6 has been made available.
If the provider is available for previous versions of EF, then we encourage you to contact the owner of the provider and ask them to create an EF6 version. You should include a reference to the documentation for the EF6 provider model.
It is certainly possible to create an EF provider yourself although it should not be considered a trivial undertaking. The the link above about the EF6 provider model is a good place to start. You may also find it useful to use the code for the SQL Server and SQL CE provider included in the EF open source project on CodePlex as a starting point or for reference.
Note that starting with EF6 the EF provider is less tightly coupled to the underlying ADO.NET provider. This makes it easier to write an EF provider without needing to write or wrap the ADO.NET classes.