Thanks @sethmlarson ! Responses to your questions:

• Yes, async search also has a knn property. Overall async search accepts the exact same search requests as the main _search endpoint, including all options.
• The filter key should indeed be there. It is documented here (you could search for knn within the page): https://www.elastic.co/guide/en/elasticsearch/reference/master/search-search.html.

@jtibshirani Sorry, my second question was a bit ambiguous. I was asking about the knn section under QueryContainer. I'm asking if the below is a valid search request body:

POST /<index>/_search
{
  "query": {
    "knn": {
      "field": "...",
      ...
    }
  }
}

No, this is not valid. The knn section is a new top-level section in the search request. There is no such thing as a knn query type right now.

@jtibshirani That's what I thought, it looks like that snuck into the spec in a previous review.

@swallez Thanks for the review, I've updated the PR with your comments.

Following you can find the validation results for the APIs you have changed.

You can validate these APIs yourself by using the make validate target.