Shameless plug: we built our own open source equivalent of auto-ontology a few months ago, that doesn't require any API key but your LLM one (or none if you use your coding agent subscription)

https://github.com/GetCassis/ontology-skills

I've not tried running it but while it defaults to NVIDIA hosted endpoints but the readme suggests you can host those yourself if you want.

You can self-host the LLMs involved, API key is only if you're using nvidia-hosted