Symfony 4.0 Roadmap
Symfony manages its releases through a time-based model. A new Symfony minor version comes out every six months, one in May and one in November. Check out the release process details.
Support for Symfony 4.0 ended in January 2019.
You should upgrade to 4.2 version.
Roadmap
Nov 2017 Release
Jul 2018 End of support for bug fixes
Jan 2019 End of support for security fixes
Check other Symfony versions
Latest Symfony versions
Maintained Symfony branches
These are the Symfony branches currently supported for bug fixes. Check out the Symfony release process for the full details.