Last fall the PHP core team voted to pick a distributed version control system and git won handily.
David Soria Parra, the release manager of PHP 5.4, has put together a workflow for core committers merging GitHub pull requests into PHP.
Using github was one of the most important reasons to switch to git in the first place.
The php-src repository is 13 years old and includes over 80k commits. Maybe the next commit will be yours?
Welcome to GitHub, PHP. Let the forking begin!