diff --git a/internal/translator/claude/openai/responses/claude_openai-responses_request.go b/internal/translator/claude/openai/responses/claude_openai-responses_request.go
index d37b7156..61f5c1a0 100644
--- a/internal/translator/claude/openai/responses/claude_openai-responses_request.go
+++ b/internal/translator/claude/openai/responses/claude_openai-responses_request.go
@@ -622,6 +622,51 @@ func qualifyResponsesNamespaceToolName(namespaceName, childName string) string {
 	return namespaceName + "__" + childName
 }
 
+func splitResponsesQualifiedFunctionCallFromRequest(requestRawJSON []byte, qualifiedName string) (name, namespace string) {
+	qualifiedName = strings.TrimSpace(qualifiedName)
+	if qualifiedName == "" {
+		return "", ""
+	}
+
+	tools := gjson.GetBytes(requestRawJSON, "tools")
+	if !tools.Exists() || !tools.IsArray() {
+		return qualifiedName, ""
+	}
+
+	var bestNamespace string
+	var bestChild string
+	tools.ForEach(func(_, tool gjson.Result) bool {
+		if strings.TrimSpace(tool.Get("type").String()) != "namespace" {
+			return true
+		}
+		namespaceName := strings.TrimSpace(tool.Get("name").String())
+		if namespaceName == "" {
+			return true
+		}
+		children := tool.Get("tools")
+		if !children.Exists() || !children.IsArray() {
+			return true
+		}
+		children.ForEach(func(_, child gjson.Result) bool {
+			childName := responsesToolName(child)
+			if childName == "" {
+				return true
+			}
+			if qualifyResponsesNamespaceToolName(namespaceName, childName) == qualifiedName {
+				bestNamespace = namespaceName
+				bestChild = childName
+			}
+			return true
+		})
+		return true
+	})
+
+	if bestNamespace == "" || bestChild == "" {
+		return qualifiedName, ""
+	}
+	return bestChild, bestNamespace
+}
+
 func isUnsupportedOpenAIBuiltinToolType(toolType string) bool {
 	switch toolType {
 	case "image_generation", "file_search", "code_interpreter", "computer_use_preview":
diff --git a/internal/translator/claude/openai/responses/claude_openai-responses_response.go b/internal/translator/claude/openai/responses/claude_openai-responses_response.go
index 97256687..c27cb4b3 100644
--- a/internal/translator/claude/openai/responses/claude_openai-responses_response.go
+++ b/internal/translator/claude/openai/responses/claude_openai-responses_response.go
@@ -89,6 +89,23 @@ func pickRequestJSON(originalRequestRawJSON, requestRawJSON []byte) []byte {
 	return nil
 }
 
+func applyResponsesFunctionCallNamespaceFields(item []byte, requestRawJSON []byte, qualifiedName string, itemPath string) []byte {
+	name, namespace := splitResponsesQualifiedFunctionCallFromRequest(requestRawJSON, qualifiedName)
+	namePath := "name"
+	namespacePath := "namespace"
+	if itemPath != "" {
+		namePath = itemPath + ".name"
+		namespacePath = itemPath + ".namespace"
+	}
+	item, _ = sjson.SetBytes(item, namePath, name)
+	if namespace != "" {
+		item, _ = sjson.SetBytes(item, namespacePath, namespace)
+	} else {
+		item, _ = sjson.DeleteBytes(item, namespacePath)
+	}
+	return item
+}
+
 func emitEvent(event string, payload []byte) []byte {
 	return translatorcommon.SSEEventData(event, payload)
 }
@@ -236,7 +253,7 @@ func ConvertClaudeResponseToOpenAIResponses(ctx context.Context, modelName strin
 			item, _ = sjson.SetBytes(item, "output_index", idx)
 			item, _ = sjson.SetBytes(item, "item.id", fmt.Sprintf("fc_%s", st.CurrentFCID))
 			item, _ = sjson.SetBytes(item, "item.call_id", st.CurrentFCID)
-			item, _ = sjson.SetBytes(item, "item.name", name)
+			item = applyResponsesFunctionCallNamespaceFields(item, pickRequestJSON(originalRequestRawJSON, requestRawJSON), name, "item")
 			out = append(out, emitEvent("response.output_item.added", item))
 			if st.FuncArgsBuf[idx] == nil {
 				st.FuncArgsBuf[idx] = &strings.Builder{}
@@ -350,7 +367,7 @@ func ConvertClaudeResponseToOpenAIResponses(ctx context.Context, modelName strin
 			itemDone, _ = sjson.SetBytes(itemDone, "item.id", fmt.Sprintf("fc_%s", st.CurrentFCID))
 			itemDone, _ = sjson.SetBytes(itemDone, "item.arguments", args)
 			itemDone, _ = sjson.SetBytes(itemDone, "item.call_id", st.CurrentFCID)
-			itemDone, _ = sjson.SetBytes(itemDone, "item.name", st.FuncNames[idx])
+			itemDone = applyResponsesFunctionCallNamespaceFields(itemDone, pickRequestJSON(originalRequestRawJSON, requestRawJSON), st.FuncNames[idx], "item")
 			out = append(out, emitEvent("response.output_item.done", itemDone))
 			st.InFuncBlock = false
 		} else if st.ReasoningActive {
@@ -512,7 +529,7 @@ func ConvertClaudeResponseToOpenAIResponses(ctx context.Context, modelName strin
 				item, _ = sjson.SetBytes(item, "id", fmt.Sprintf("fc_%s", callID))
 				item, _ = sjson.SetBytes(item, "arguments", args)
 				item, _ = sjson.SetBytes(item, "call_id", callID)
-				item, _ = sjson.SetBytes(item, "name", name)
+				item = applyResponsesFunctionCallNamespaceFields(item, reqBytes, name, "")
 				outputsWrapper, _ = sjson.SetRawBytes(outputsWrapper, "arr.-1", item)
 			}
 		}
@@ -794,7 +811,7 @@ func ConvertClaudeResponseToOpenAIResponsesNonStream(_ context.Context, _ string
 			item, _ = sjson.SetBytes(item, "id", fmt.Sprintf("fc_%s", st.id))
 			item, _ = sjson.SetBytes(item, "arguments", args)
 			item, _ = sjson.SetBytes(item, "call_id", st.id)
-			item, _ = sjson.SetBytes(item, "name", st.name)
+			item = applyResponsesFunctionCallNamespaceFields(item, reqBytes, st.name, "")
 			outputsWrapper, _ = sjson.SetRawBytes(outputsWrapper, "arr.-1", item)
 		}
 	}
diff --git a/internal/translator/claude/openai/responses/claude_openai-responses_response_test.go b/internal/translator/claude/openai/responses/claude_openai-responses_response_test.go
index addf4de1..9db2e058 100644
--- a/internal/translator/claude/openai/responses/claude_openai-responses_response_test.go
+++ b/internal/translator/claude/openai/responses/claude_openai-responses_response_test.go
@@ -246,3 +246,103 @@ func TestConvertClaudeResponseToOpenAIResponsesNonStream_ReportsCacheTokens(t *t
 		t.Fatalf("non-stream usage total_tokens = %d, want %d", got, 22048)
 	}
 }
+
+func TestConvertClaudeResponseToOpenAIResponses_RestoresNamespaceFunctionCall(t *testing.T) {
+	originalRequest := []byte(`{
+		"model":"gpt-test",
+		"tools":[
+			{
+				"type":"namespace",
+				"name":"mcp__node_repl",
+				"tools":[{"type":"function","name":"js","parameters":{"type":"object","properties":{}}}]
+			}
+		]
+	}`)
+	chunks := [][]byte{
+		[]byte(`data: {"type":"message_start","message":{"id":"msg_123","usage":{"input_tokens":1,"output_tokens":0}}}`),
+		[]byte(`data: {"type":"content_block_start","index":1,"content_block":{"type":"tool_use","id":"call_abc","name":"mcp__node_repl__js","input":{}}}`),
+		[]byte(`data: {"type":"content_block_delta","index":1,"delta":{"type":"input_json_delta","partial_json":"{"code":"nodeRepl.write('hello')"}"}}`),
+		[]byte(`data: {"type":"content_block_stop","index":1}`),
+		[]byte(`data: {"type":"message_stop"}`),
+	}
+
+	var param any
+	var added gjson.Result
+	var done gjson.Result
+	var completed gjson.Result
+	for _, chunk := range chunks {
+		for _, output := range ConvertClaudeResponseToOpenAIResponses(context.Background(), "claude-test", originalRequest, nil, chunk, &param) {
+			event, data := parseClaudeResponsesSSEEvent(t, output)
+			switch event {
+			case "response.output_item.added":
+				if data.Get("item.type").String() == "function_call" {
+					added = data
+				}
+			case "response.output_item.done":
+				if data.Get("item.type").String() == "function_call" {
+					done = data
+				}
+			case "response.completed":
+				completed = data
+			}
+		}
+	}
+
+	for _, tc := range []struct {
+		label string
+		got   gjson.Result
+	}{
+		{"added", added},
+		{"done", done},
+	} {
+		if !tc.got.Exists() {
+			t.Fatalf("expected function_call %s event", tc.label)
+		}
+		if got := tc.got.Get("item.name").String(); got != "js" {
+			t.Fatalf("%s item.name = %q, want js", tc.label, got)
+		}
+		if got := tc.got.Get("item.namespace").String(); got != "mcp__node_repl" {
+			t.Fatalf("%s item.namespace = %q, want mcp__node_repl", tc.label, got)
+		}
+	}
+
+	if !completed.Exists() {
+		t.Fatal("expected response.completed event")
+	}
+	if got := completed.Get("response.output.0.name").String(); got != "js" {
+		t.Fatalf("completed output name = %q, want js", got)
+	}
+	if got := completed.Get("response.output.0.namespace").String(); got != "mcp__node_repl" {
+		t.Fatalf("completed output namespace = %q, want mcp__node_repl", got)
+	}
+}
+
+func TestConvertClaudeResponseToOpenAIResponsesNonStream_RestoresNamespaceFunctionCall(t *testing.T) {
+	originalRequest := []byte(`{
+		"model":"gpt-test",
+		"tools":[
+			{
+				"type":"namespace",
+				"name":"mcp__node_repl",
+				"tools":[{"type":"function","name":"js","parameters":{"type":"object","properties":{}}}]
+			}
+		]
+	}`)
+	raw := []byte(strings.Join([]string{
+		`data: {"type":"message_start","message":{"id":"msg_nonstream","usage":{"input_tokens":1,"output_tokens":0}}}`,
+		`data: {"type":"content_block_start","index":1,"content_block":{"type":"tool_use","id":"call_abc","name":"mcp__node_repl__js","input":{}}}`,
+		`data: {"type":"content_block_delta","index":1,"delta":{"type":"input_json_delta","partial_json":"{\"code\":\"nodeRepl.write('hello')\"}"}}`,
+		`data: {"type":"content_block_stop","index":1}`,
+		`data: {"type":"message_stop"}`,
+	}, "\n"))
+
+	out := ConvertClaudeResponseToOpenAIResponsesNonStream(context.Background(), "claude-test", originalRequest, nil, raw, nil)
+	root := gjson.ParseBytes(out)
+
+	if got := root.Get("output.0.name").String(); got != "js" {
+		t.Fatalf("non-stream output name = %q, want js", got)
+	}
+	if got := root.Get("output.0.namespace").String(); got != "mcp__node_repl" {
+		t.Fatalf("non-stream output namespace = %q, want mcp__node_repl", got)
+	}
+}