Good Job. How many PHP packages are on packagist.org? Is it just based on GitHub? Does it just link to tags on GitHub? Or does it host real binaries like Maven

Good Job. How many PHP packages are on packagist.org? Is it just based on GitHub? Does it just link to tags on GitHub? Or does it host real binaries like Maven2, RubyGems and PIP? The most important feature of a good package manager is that released packages are not anymore changeable. With GitHub tags that is not the case. I am looking forward to the answers.