As mentioned, the AI plugins can use external services or you can create your own personal cloud system that performs the same tasks. However, running your own AI service is costly, requires extra maintenance and doesn’t give you comparable results to external services.
This is all a limitation of the AI technology itself that it is so challenging to maintain and run, not anything Discourse can do about that. The Discourse plugins are agnostic as to whether you are using an external service or an “internal” one