@xuwei-k I just ran some tests and sbt definitely updates itself. I'm not seeing where this is necessary. We've run into issues in the past with incompatibilities and have since been resolved by the auto-updating behavior. In other words, the following works with 0.11-0.13:
https://github.com/naaman/heroku-buildpack-scala/commit/d85cb8c8a6c58b26905aef3e8f4480b57e123a4d