It’s sometimes unstable. But sometimes it’s mostly stable.

testing, stable, oldstable, etc are pointers to named branches (named after Toy Story characters BTW). Unstable is also a pointer but it always points to sid (the neighbour kid that breaks the toys).

Testing isn’t a rolling release. Yesterday testing pointed to trixie. Today stable points to trixie (because testing was completed and trixie has been “released”) and testing now points to forky which is a new branch that is basically a copy of unstable. They’ll do testing on forky and fix things and eventually stable will be pointed at forky (which will be Debian 14) and they’ll make a new testing branch called something else.

It’s an odd thing to call things “released” on a project that’s done openly. Debian 13 was just released today, but you can install what will be Debian 14 right now long before it’s released by installing forky. You can also contribute to their testing by submitting bug reports. But if you do install forky (testing) today, don’t be too disappointed if there’s a bunch of things broken because it’s the same as unstable right now. It will get more reliable as things are fixed and eventually be considered as stable. When Debian 14 is “released” you won’t need to upgrade anything if you’re on forky because you’ll have already been on it for a year or more.

But yeah, unstable is unstable, it’s just somewhere people can chuck packages on and experiment. Things will break there. Testing is testing, it’s there if you want to help out with testing. And stable is stable, you get that if you want something reliable and you don’t want to mess around with software occasionally breaking and having to track down what broke and submit bug reports.