Put simply, you shouldn't ever be afraid to upgrade as long as you're only using our public APIs.
Whenever there is a need to break compatibility, it is announced in the changelog, and raises a `DeprecationWarning` for a year (if possible) before it's finally really broken.
> **Warning**
> The structure of the `attrs.Attribute` class is exempt from this rule.
> It *will* change in the future, but since it should be considered read-only, that shouldn't matter.
>
> However if you intend to build extensions on top of *attrs* you have to anticipate that.