Vision plugins must implement one of the versions of the api. Vision will be backward compatible so if the vision-cli tool is on v2, it will continue to support v1. This does not mean the api spec is backward compatible, only that the tool will detect that a plugin or project is on a previous version and will execute the appropriate code.
Plugins must return the message structs which will be serialized into json during communication between the vision-cli and the plugins. Standard vision plugins including project, service, graphql, gateway, etc also implement this interface