Debian Unstable is a rolling distribution used for Debian development and recommended for advanced users in FreeCAD development and packaging. New packages are ready as soon as they are uploaded and built, unless the uploader has marked them for Debian Experimental which requires explicit installation (after some setup to enable the extra distribution) via
sudo apt install -t experimental <packagename>.
Frequently, people using Debian Testing should actually use Debian Unstable; Debian Testing should only be considered a "QA release pocket", since, while it may appear to be more stable than Unstable, there's actually a downside. New packages are uploaded to Debian Unstable and migrate to Testing after some time, and so security fixes and important packaging changes can be inappropriately delayed.
There are two key things to a good user experience in Unstable. The first is to never blindly run
sudo apt full-upgrade or its equivalents without first checking the results of the operation. If it's saying you'll free up hundreds of MB of space, there's a package transition underway which will remove a good portion of your system. Instead, one can safely run
sudo apt upgrade and get new packages. Sometimes, this will result in packages being held back, which means it may be appropriate to run
full-upgrade as package uninstallation may actually be necessary.
The second key is to embrace that you're taking part in Debian development, and use the appropriate tools and methods. For example, that may mean installing packages like
apt-listchanges or subscribing to Debian mailing lists like email@example.com.
While Debian Unstable is perfectly suitable as a long-term daily driver, it's also very easy to run in a virtual machine, where breakages won't be such a big deal. Simply download a Debian Testing ISO, install it into a VM and update it, and then edit
/etc/apt/sources.list to contain something like:
deb http://ftp.us.debian.org/debian/ testing main contrib non-free # deb-src http://ftp.us.debian.org/debian/ testing main contrib non-free deb http://security.debian.org/debian-security testing/updates main contrib non-free # deb-src http://security.debian.org/debian-security testing/updates main contrib non-free deb http://ftp.us.debian.org/debian/ unstable main contrib non-free # deb-src http://ftp.us.debian.org/debian/ unstable main contrib non-free
If you want to enable packages from Experimental, put this into
deb http://deb.debian.org/debian experimental main contrib non-free # deb-src http://deb.debian.org/debian experimental main contrib non-free