Check the blog post for links to all the CHANGELOGs. As Rails 5 was released, this is probably going to be the last release of Rails 4.1. Please take some time to upgrade your application to Rails 4.2 or Rails 5.
The documentation states that AR::to_param should truncate values longer than 20 characters by words. This commit enforces this behavior, using as many characters as possible to maximize the information included in the URL.
The encoding of path parameters is now checked earlier in the dispatch process so that routes that go directly to a Rack app, or skip controller instantiation, don't have to defend themselves against non-UTF8 characters.