Ruby 2.4 is the latest stable version of Ruby. Many new features and improvements are included, for example:
hash table improvements
unify Fixnum and Bignum into Integer
String supports Unicode case mappings
performance and debugging improvements
Ruby 2.4 includes updates to soname and so Ruby packages that use binary extensions should be rebuilt. Nevertheless, since the Ruby community paid great attention to source compatibility, no changes to your code are needed.
More information about Ruby 2.4 can be found in the Ruby community’s Ruby 2.4.0 Release Notes.