Do we really need to build 2.11 on sbt 0.13.0-RC3. I have no qualms with building with a master for an unstable version of the compiler (here 2.11) — though I do think like @skyluc as far as stable strands of underlying components are concerned (here, the 2.10.x profile). That is, I would have put 0.13.0-SNAPSHOT here.