Yes, the 2.1.0 client should be compatible with 2.4.0, you may just not be able to access the latest 2.4.0 features but the existing ones should be working just fine (README has to be updated). Thanks.
that’s good news, thanks! One feature that we are currently missing, is a replacement for the RHLC BulkProcessor. Do you (or anybody else) know if there are any plans for a successor in opensearch-java?