Amazon KnowledgeBase with OpenSearchServerless - minimum price

Hello.

I think a minimum of 4 OCU is correct.
OpenSearch Serverless has a minimum size of 4 OCU, 2 OCU for indexing and 2 OCU for searching.
https://docs.aws.amazon.com/opensearch-service/latest/developerguide/serverless-scaling.html

When you create your first collection, OpenSearch Serverless instantiates a total of four OCUs (two for indexing and two for search). These OCUs always exist, even when there's no indexing or search activity. All subsequent collections can share these OCUs (except for collections with unique AWS KMS keys, which instantiate their own set of four OCUs). If needed, OpenSearch Serverless automatically scales out and adds additional OCUs as your indexing and search usage grows. When traffic on your collection endpoint decreases, capacity scales back down to the minimum number of OCUs required for your data size. At most, it will scale down to 2 OCUs for indexing and 2 OCUs for search.