(Kagi User since two years)

The assistant beta was ~1 year in beta.

Assistant had many bugs in the early stages, but it's different kind of beast than Search API (more things that can go wrong). With Search API it's probably "only" billing/UI bugs which they want to catch in the beta and maybe some problems with the search results from the API endpoint

Though in this case I'd say a few weeks, maybe 2 months. (They keep things in beta longer than it needs to be, to be completely sure nothing goes haywire especially if it's billing related like the pay per use API endpoint).