On the Symfony blog they've posted the official announcement about the release of Symfony 4.0.0, the latest major version of the popular framework.

Symfony 4.0.0 has just been released. [...] Read the Hello Symfony 4! blog post for a quick overview of the best new features of Symfony 4 and the best way to upgrade your existing applications to Symfony 4.

The post includes a listing of the items fixed since the previous version and links to an upgrade guide that can help you bring your apps up and working in this latest version.