[FEATURE] Support of agentic search queries for conversational agents

[ocuenca-coursera]

Is your feature request related to a problem?

OpenSearch 3.2+ introduced the agentic query type, a specialized query that translates natural language questions into DSL queries via a preconfigured agent and search pipeline. The OpenSearch Java client does not currently support this query type, forcing users to fall back on raw JSON or low-level REST calls to use agentic search from Java applications.

What solution would you like?

Add AgenticQuery as a new variant of the Query tagged union in the Java client, following the same patterns used by existing query types like HybridQuery. The query should support the following fields:

Field	Type	Required	Description
query_text	String	Yes	The natural language question
query_fields	List<String>	No	Index fields the agent should consider
memory_id	String	No	Memory ID for conversational context

Here's how to use it:

  import org.opensearch.client.opensearch.OpenSearchClient;                                                                                                                                                                                                                                                               
  import org.opensearch.client.opensearch.core.SearchRequest;                                                                                                                                                                                                                                                             
  import org.opensearch.client.opensearch.core.SearchResponse;                                                                                                                                                                                                                                                            
  import org.opensearch.client.opensearch._types.query_dsl.AgenticQuery;                                                                                                                                                                                                                                                  
                                                                                                                                                                                                                                                                                                                          
  // Build and execute the search request
  SearchResponse<MyDocument> response = client.search(s -> s
      .index("my-index")
      .searchPipeline("my-agentic-pipeline")
      .query(q -> q
          .agentic(a -> a
              .queryText("What is the best selling product last quarter?")
              .queryFields("title", "description", "category")
              .memoryId("conversation-abc-123")
          )
      ),
      MyDocument.class
  );

This involves:

• Creating AgenticQuery.java (with builder, serialization/deserialization, and QueryVariant implementation)
• Registering the Agentic kind in Query.java (enum value, getters, builder methods, deserializer)
• Adding a convenience factory method in QueryBuilders.java
• Adding a unit test (AgenticQueryTest.java)

What alternatives have you considered?

• Using JsonData / raw JSON queries: Users can construct agentic queries as raw JSON via the wrapper query or low-level REST client, but this bypasses the type-safe builder API and loses IDE autocompletion, compile-time validation, and consistency with the rest of the client.
• Waiting for code generation: The client code is partially generated from the OpenSearch spec. However, the spec may not yet include the agentic query definition, so a manual addition unblocks users sooner.

Do you have any additional context?

• OpenSearch agentic query documentation: https://docs.opensearch.org/latest/query-dsl/specialized/agentic/
• The implementation follows the same conventions as HybridQuery, which was also added as a manual extension to the generated client code.

[andrross]

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