Symfony 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 document for the full timeline details.
Latest Symfony versions
long term support version
2.7.3for projects that prioritize very long support over new features
stable version
2.7.3for projects that need the latest Symfony features
development version
2.8.0-devfor testing projects with the upcoming Symfony version
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Symfony version checker
Symfony 2.7 is the latest stable version and it will be maintained until the end of May 2019.
Roadmap
May 2015 Release
May 2018 End of support for bug fixes
May 2019 End of support for security fixes