On the Symfony blog there's a new post talking about the upcoming feature freeze for Symfony 3.4 and 4.0.
Symfony project follows a time-based development process where two new minor versions are released each year and a major version is released every two years.
This year, Symfony 3.4 and Symfony 4.0 will be both released at the end of November 2017. The only difference between both versions is that 3.4 includes all features deprecated in 3.x branches and 4.0 removes them.
Two months before their final releases, Symfony versions enter into a "feature freeze" period. During this time, we can't add new features and we solely focus on polishing and stabilizing the new features (and even reverting them if they don't work properly).
In other words, this week is our last chance to add new features to Symfony 3.4 and 4.0.
The post lists out a few ways that you can help out including reviewing pull requests and issues to see if there's anything that might be missing from these releases and might need to be integrated pre-freeze.