It is just a version schema. A version is dictated "stable" when tests pass or confidence in the code at that release is high. They could have easily started with version 1.0.0 and currently be on version 1.13.2. The version number doesn't directly dictate stability.
Does that mean that they suggest I can use this in production (since it's "stable") or that I can't, since it's not at version 1 yet?