Thanks!
This could use a tutorial on the significance of why this is important, how to construct queries, which seem to be a prompt, and how it could be used to enhance ones Discourse forum.
Also, if one changes the AI model say from OpenAI GPT to Claude, then the embeddings would be different so the impacts of such a change should be noted in a tutorial.
I do hang out on a Zulip forum (Lean) and surely miss the AI features that Discourse has. (Zulip feature matrix)
meaning the feature does not exist.
Hats off to the Discourse staff on augmenting with AI.
IIRC the use of this is free because the cost of embeddings is so cheap now that it is not worth charging. 
Obviously the Discourse staff need to clarify that statement but I am sure others might be surprised at the answer.
Out of curiosity I tried the URL on a Discourse site where I am just a Trust Level 1 (Basic user) and the query worked.
Since this seems to be enabled and available by default, in the back of my mind I tend to consider if such technology is of benefit to the blind trying to use the internet, this is obviously a win for them when the dots are connected meaning if they are made aware of this then they or others can make use of it to help them.
As such noted this in a topic for the blind on the OpenAI forum.