Release process documentation is in progress, see PR 5252.
Early releases require heavy testing, especially across various system setups. We ❤️ testers, and are big fans of anyone who can run gem install bundler --pre and try out upcoming releases in their development and staging environments.
There may not always be prereleases or beta versions of Bundler. The Bundler team will tweet from the @bundlerio account when a prerelease or beta version becomes available. You are also always welcome to try checking out master and building a gem yourself if you want to try out the latest changes.