I would not put the version number in the API. If you release a version that is not backward compatible, the user does not need to upgrade. But if you make a release is backward compatible, such as a bug fix version, you will force the user to change their package names without just being able to drop in a new jar.
Build tools (ant, maven, gradle, etc) are used for managing versions. You shouldn't need to do so in your API package names.