Since the latest version of Babel stating 'Babel required' in the koa docs is no longer meaningful as by default it does nothing, and you have to configure which syntax it should transpile. At the very least koa needs to document which plugins are required. Even better would be a table indicating which plugins are required for given environments (e.g. none are needed for koa 1 on node 4, but very many are needed for koa 2 on 0.12... I'm currently struggling to figure out what babel transforms are needed to run koa 2 on node 5)