[If I put this on the wrong component, can someone please update?]
Major versions of scala are not forward nor backwards compatible. Libraries build for 2.10 will not work with 2.11 or vice versa.
In order to avoid build related problems, it is strongly recommended to append the scala version it is compatible within the artifact id. This ensures the correct version of the library is pulled in rather than deferring the problem to a future build or runtime error.
For example, akka exposes the following packages for the same version: