The type for the SubmitAsyncSearchRequest.Knn and MultisearchBody.Knn properties has changed to an ICollection<KnnQuery> from a single KnnQuery since it is possible to include more than one query in a request.

Before

public sealed partial class SubmitAsyncSearchRequest
{
   ...
   public Elastic.Clients.Elasticsearch.KnnQuery? Knn { get; set; }
   ...
}

public sealed partial class MultisearchBody
{
   ...
   public Elastic.Clients.Elasticsearch.KnnQuery? Knn { get; set; }
   ...
}

After

public sealed partial class SubmitAsyncSearchRequest
{
   ...
   public ICollection<Elastic.Clients.Elasticsearch.KnnQuery>? Knn { get; set; }
   ...
}

public sealed partial class MultisearchBody
{
   ...
   public ICollection<Elastic.Clients.Elasticsearch.KnnQuery>? Knn { get; set; }
   ...
}

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