As announced during SymfonyWorld, the Symfony CLI code is now Open-Source. You can find the code on Github.
The code that I open-sourced today has evolved a lot since the fork from the proprietary code. The main differences are the following:
The auto-update code has been replaced by Goreleaser (we provide way more options now including Homebrew, deb, rpm, and Windows packages);
The new code supports Platform.sh out of the box (as the replacement for SymfonyCloud, which is not supported anymore);
Some libraries have been extracted (all under the Symfony CLI organization) as they might be useful on their own;
The code has been modernized and cleaned up from obsolete code.
Open-sourcing such a large code base took me many months of careful planning and work. I'm happy that the code is now open-source and
I'm eager to see how you will contribute to make it better. There are so many changes I'd like to make that I would love to see how to see out great community at work.