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 version2.3.20
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 2.5 is the latest stable version and it will be maintained until the end of July 2015.
May 2014 Release
Jan 2015 End of support for bug fixes
Jul 2015 End of support for security fixes