React and Redux are both popular and widely used, and this is the official library that ties the two together. Also, it's absolutely a major update. The API is almost identical (with one new function), but the internals were completely rewritten, with potentially different (but better) behavior in a few edge cases. It also offers improved performance in most cases.

See https://github.com/reactjs/react-redux/pull/416 for the nitty-gritty details of what was involved.