I've implemented AI on my forum through my exclusive partnership with Xpertloop, using their API, which is using open.ai / GPT5.
[edit: Importantly, we had Xpertloop ingest my forum's content, so that it can provide responses prioritized with my forum's content, and if not enough context is provided, it falls back on ChatGPT (other models can be used as the backup, e.g. Claude, etc). I can set up multiple agents for different topics, but for now I just have one general agent to set tone, tenor, rules and formats, etc.]
I am thinking about packaging the solution as an addon, and offering onboarding and ongoing support.