The Bundler 1.16 announcement includes context and a more detailed explanation of the changes in this version. This is a summary of the biggest changes. As always, a detailed list of every change is provided in the changelog.
By replacing the heuristic-focused “swapping” algorithm with one that can consider groups of gems at once, Grey Baker managed to eliminate many bugs around dependency resolution, all while making resolution faster than ever before.
We've managed to reduce the number of times a Gemfile needs to be `eval`ed when running `bundle install`. Additionally, running `bundle install` when no installation needs to be done is several times faster, bringing it within a few hundred milliseconds of `bundle check`.