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.
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long term support version2.3.28
for projects that prioritize very long support over new features
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for testing projects with the upcoming Symfony version
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Symfony 2.6 is the latest stable version and it will be maintained until the end of January 2016.
Nov 2014 Release
Jul 2015 End of support for bug fixes
Jan 2016 End of support for security fixes