Most of of the current Squid developmens are hosted here on devel.squid-cache.org. This service is built around the service provided by SourceForge.
The current Squid development model makes extensive use of branches, where each developer or task is given a unique branch containing his changes. Tools are provided to almost automatically keep the development branches up to date with the main Squid version.
To become a Squid developer you need to have a registered SourceForge account, and then email squid-dev@squid-cache.org with your account name and a short introduction on who you are and your interest in Squid development. You will then be given access to the development CVS repository.
Developers are assumed to know and follow these simple rules (separate page)
And to use these tools (separate page) to maintain their work in the CVS repository.