diff --git a/contrib/mark3labs/mcp-go/mcpgo.go b/contrib/mark3labs/mcp-go/mcpgo.go
index fe9ec4dccf..f2214e4fbc 100644
--- a/contrib/mark3labs/mcp-go/mcpgo.go
+++ b/contrib/mark3labs/mcp-go/mcpgo.go
@@ -59,6 +59,8 @@ func NewToolHandlerMiddleware() server.ToolHandlerMiddleware {
 				outputText = string(resultJSON)
 			}
 
+			tagWithSessionID(ctx, toolSpan)
+
 			toolSpan.AnnotateTextIO(string(inputJSON), outputText)
 
 			if err != nil {
@@ -86,6 +88,7 @@ func (h *hooks) onBeforeInitialize(ctx context.Context, id any, request *mcp.Ini
 	taskSpan.Annotate(llmobs.WithAnnotatedTags(map[string]string{"client_name": clientName, "client_version": clientName + "_" + clientVersion}))
 
 	h.spanCache.Store(id, taskSpan)
+	tagWithSessionID(ctx, taskSpan)
 }
 
 func (h *hooks) onAfterInitialize(ctx context.Context, id any, request *mcp.InitializeRequest, result *mcp.InitializeResult) {
@@ -114,6 +117,14 @@ func (h *hooks) onError(ctx context.Context, id any, method mcp.MCPMethod, messa
 	span.Finish(llmobs.WithError(err))
 }
 
+func tagWithSessionID(ctx context.Context, span llmobs.Span) {
+	session := server.ClientSessionFromContext(ctx)
+	if session != nil {
+		sessionID := session.SessionID()
+		span.Annotate(llmobs.WithAnnotatedTags(map[string]string{"mcp_session_id": sessionID}))
+	}
+}
+
 func finishSpanWithIO[Req any, Res any](h *hooks, id any, request Req, result Res) {
 	value, ok := h.spanCache.LoadAndDelete(id)
 	if !ok {
diff --git a/contrib/mark3labs/mcp-go/mcpgo_test.go b/contrib/mark3labs/mcp-go/mcpgo_test.go
index 1be3a419bb..678feb6974 100644
--- a/contrib/mark3labs/mcp-go/mcpgo_test.go
+++ b/contrib/mark3labs/mcp-go/mcpgo_test.go
@@ -52,6 +52,11 @@ func TestIntegrationSessionInitialize(t *testing.T) {
 		server.WithHooks(hooks))
 
 	ctx := context.Background()
+	sessionID := "test-session-init"
+	session := &mockSession{id: sessionID}
+	session.Initialize()
+	ctx = srv.WithContext(ctx, session)
+
 	initRequest := `{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test-client","version":"1.0.0"}}}`
 
 	response := srv.HandleMessage(ctx, []byte(initRequest))
@@ -77,6 +82,8 @@ func TestIntegrationSessionInitialize(t *testing.T) {
 	assert.Contains(t, taskSpan.Tags, "client_name:test-client")
 	assert.Contains(t, taskSpan.Tags, "client_version:test-client_1.0.0")
 
+	assert.Contains(t, taskSpan.Tags, "mcp_session_id:test-session-init")
+
 	assert.Contains(t, taskSpan.Meta, "input")
 	assert.Contains(t, taskSpan.Meta, "output")
 
@@ -101,7 +108,11 @@ func TestIntegrationToolCallSuccess(t *testing.T) {
 	tt := testTracer(t)
 	defer tt.Stop()
 
+	hooks := &server.Hooks{}
+	AddServerHooks(hooks)
+
 	srv := server.NewMCPServer("test-server", "1.0.0",
+		server.WithHooks(hooks),
 		server.WithToolHandlerMiddleware(NewToolHandlerMiddleware()))
 
 	calcTool := mcp.NewTool("calculator",
@@ -133,9 +144,13 @@ func TestIntegrationToolCallSuccess(t *testing.T) {
 	session.Initialize()
 	ctx = srv.WithContext(ctx, session)
 
+	initRequest := `{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test-client","version":"1.0.0"}}}`
+	response := srv.HandleMessage(ctx, []byte(initRequest))
+	assert.NotNil(t, response)
+
 	toolCallRequest := `{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"calculator","arguments":{"operation":"add","x":5,"y":3}}}`
 
-	response := srv.HandleMessage(ctx, []byte(toolCallRequest))
+	response = srv.HandleMessage(ctx, []byte(toolCallRequest))
 	assert.NotNil(t, response)
 
 	responseBytes, err := json.Marshal(response)
@@ -147,10 +162,25 @@ func TestIntegrationToolCallSuccess(t *testing.T) {
 	assert.Equal(t, "2.0", resp["jsonrpc"])
 	assert.NotNil(t, resp["result"])
 
-	spans := tt.WaitForLLMObsSpans(t, 1)
-	require.Len(t, spans, 1)
+	spans := tt.WaitForLLMObsSpans(t, 2)
+	require.Len(t, spans, 2)
+
+	var initSpan, toolSpan *testtracer.LLMObsSpan
+	for i := range spans {
+		if spans[i].Name == "mcp.initialize" {
+			initSpan = &spans[i]
+		} else if spans[i].Name == "calculator" {
+			toolSpan = &spans[i]
+		}
+	}
+
+	require.NotNil(t, initSpan, "initialize span not found")
+	require.NotNil(t, toolSpan, "tool span not found")
+
+	expectedTag := "mcp_session_id:test-session-123"
+	assert.Contains(t, initSpan.Tags, expectedTag)
+	assert.Contains(t, toolSpan.Tags, expectedTag)
 
-	toolSpan := spans[0]
 	assert.Equal(t, "calculator", toolSpan.Name)
 	assert.Equal(t, "tool", toolSpan.Meta["span.kind"])
 
@@ -218,6 +248,8 @@ func TestIntegrationToolCallError(t *testing.T) {
 	assert.Equal(t, "error_tool", toolSpan.Name)
 	assert.Equal(t, "tool", toolSpan.Meta["span.kind"])
 
+	assert.Contains(t, toolSpan.Tags, "mcp_session_id:test-session-456")
+
 	assert.Contains(t, toolSpan.Meta, "error.message")
 	assert.Contains(t, toolSpan.Meta["error.message"], "intentional test error")
 	assert.Contains(t, toolSpan.Meta, "error.type")