[BUG] azmcp_search_knowledge_base_retrieve returning 400 bad request

[XiaoxuHU]

Describe the bug

With latest package, when using azmcp_search_knowledge_base_retrieve to retrieve knowledge base from AI Search service through MCP server. It always failed with 400 bad request

Seeing below error when enabled debug tracing

 ---> Azure.RequestFailedException: The fields 'answerInstructions', 'retrievalReasoningEffort', and 'outputMode' are not supported in this API version. Please use API version 2025-11-01-preview or later instead.
Status: 400 (Bad Request)
ErrorCode: InvalidRequestParameter

Content:
{"error":{"code":"InvalidRequestParameter","message":"The fields 'answerInstructions', 'retrievalReasoningEffort', and 'outputMode' are not supported in this API version. Please use API version 2025-11-01-preview or later instead.","details":[{"code":"InvalidAgentRetrievalRequest","message":"The fields 'answerInstructions', 'retrievalReasoningEffort', and 'outputMode' are not supported in this API version. Please use API version 2025-11-01-preview or later instead."}]}}

Headers:
Cache-Control: no-cache,no-store
Pragma: no-cache
client-request-id: c4c0fe46-9235-43af-b775-41ae5abb7a3b
x-ms-client-request-id: c4c0fe46-9235-43af-b775-41ae5abb7a3b
request-id: c4c0fe46-9235-43af-b775-41ae5abb7a3b
elapsed-time: 33
Strict-Transport-Security: REDACTED
Date: Fri, 30 Jan 2026 05:18:45 GMT
Content-Length: 474
Content-Type: application/json; charset=utf-8
Content-Language: REDACTED
Expires: -1

   at Azure.Search.Documents.KnowledgeRetrievalRestClient.RetrieveAsync(KnowledgeAgentRetrievalRequest retrievalRequest, String xMsQuerySourceAuthorization, CancellationToken cancellationToken)
   at Azure.Search.Documents.Agents.KnowledgeAgentRetrievalClient.RetrieveAsync(KnowledgeAgentRetrievalRequest retrievalRequest, String xMsQuerySourceAuthorization, CancellationToken cancellationToken)
   at Azure.Mcp.Tools.Search.Services.SearchService.RetrieveFromKnowledgeBase(String serviceName, String baseName, String query, IEnumerable`1 messages, RetryPolicyOptions retryPolicy, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at Azure.Mcp.Tools.Search.Services.SearchService.RetrieveFromKnowledgeBase(String serviceName, String baseName, String query, IEnumerable`1 messages, RetryPolicyOptions retryPolicy, CancellationToken cancellationToken)
   at Azure.Mcp.Tools.Search.Commands.Knowledge.KnowledgeBaseRetrieveCommand.ExecuteAsync(CommandContext context, ParseResult parseResult, CancellationToken cancellationToken)
[2026-01-30 05:18:45.948] [INFO] [ModelContextProtocol.Server.McpServer] Server (Azure MCP Server 2.0.0-beta.15), Client (github-copilot-developer 1.0.0) method 'tools/call' request handler completed in 2259.6423ms.

From copilot answer, it seems that MCP server need to update Azure Search SDK

This is not something you can fix in AgentChat configuration - it's an issue with the Azure MCP Server (Azure MCP Server 2.0.0-beta.15) using an older Azure Search SDK that doesn't support the latest Knowledge Base Retrieval API features.

azmcp_20260129_21.log

Expected behavior

Querying knowledge base succeed

Actual behavior

Querying knowledge base returning 400 bad request

Reproduction Steps

Invoke azmcp_search_knowledge_base_retrieve with service, knowledgeBase and query

Environment

Azure MCP Server 2.0.0-beta.15 with Github copilot sdk

[anannya03]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @pablocastro.

[pablocastro]

ACK, I confess I had a PR ready for this and then lost track of it over the holidays. Will get it refreshed and sent for review soon.