WIP: Bootstrap 3 by mdo · Pull Request #6342 · twitter/bootstrap · GitHub (github.com)
To better illustrate how we'll be developing in the future, we're using this pull request for Bootstrap 3. In the future, this will be feature-specific (e.g., a branch like 3.1.0-modal-revamp instead of n.n.n-wip).

While our last major version bump (2.0) was a complete rewrite of the docs, CSS, and JavaScript, the move to 3.0 is equally ambitious, but for a different reason: Bootstrap 3 will be mobile-first. This is an ongoing document to identify the changes we'll be making along the way.