First, allow me to share @karim.matrah’s answer here:
Indeed, this method has been released as a beta but it never really reached a point for us to be entirely trustable.
The goal for this method was to provide a kind of “recommendation API” or a “more like this query”. Basically, you give existing record content to “similarQuery” and it will try to return records that are similar to the content you specified. I would not recommend you to use this method as we are working at the moment on a brand new API for this kind of use case
While we will not prevent you from using this non-documented method, I recommend to not rely on it, as it is not officially supported and may therefore disappear at any time and without notice.
I understood that you were very interested by this feature, and asked us if you could subscribe to a early program to access it.
I’m not aware of any “early program” for this feature, but I will contact my colleagues working on the recommendation API to let them know about your interest, so that they can reach out to you when the product is ready for testing.
Have a great day!