We need to also swap out the entry point it calls. Last I looked that was a constant in the sbt code, but now I can't find it. Switching to fork would also slow us down a lot. We've tried it before and weren't very happy with performance. The bazel project recenty published how much of a speedup it gives them vs. forking: http://www.bazel.io/blog/2015/12/10/java-workers.html