diff --git a/backend/internal/pkg/apicompat/chatcompletions_responses_bridge.go b/backend/internal/pkg/apicompat/chatcompletions_responses_bridge.go
index 23178bf3a0..8aa9eab60a 100644
--- a/backend/internal/pkg/apicompat/chatcompletions_responses_bridge.go
+++ b/backend/internal/pkg/apicompat/chatcompletions_responses_bridge.go
@@ -35,8 +35,12 @@ func ResponsesToChatCompletionsRequest(req *ResponsesRequest) (*ChatCompletionsR
 	if req.Reasoning != nil {
 		out.ReasoningEffort = req.Reasoning.Effort
 	}
-	if len(req.Tools) > 0 {
-		tools, err := responsesToolsToChatTools(req.Tools)
+	effectiveTools, err := EffectiveResponsesTools(req)
+	if err != nil {
+		return nil, err
+	}
+	if len(effectiveTools) > 0 {
+		tools, err := responsesToolsToChatTools(effectiveTools)
 		if err != nil {
 			return nil, err
 		}
@@ -63,6 +67,44 @@ func ResponsesToChatCompletionsRequest(req *ResponsesRequest) (*ChatCompletionsR
 	return out, nil
 }
 
+// EffectiveResponsesTools returns every client-executable tool declared by a
+// Responses request. Newer Codex clients place their runtime tools in an
+// input item shaped as {"type":"additional_tools","tools":[...]} instead of
+// the top-level tools field. Chat-only upstreams must receive both forms.
+func EffectiveResponsesTools(req *ResponsesRequest) ([]ResponsesTool, error) {
+	if req == nil {
+		return nil, nil
+	}
+
+	tools := append([]ResponsesTool(nil), req.Tools...)
+	inputRaw := bytesTrimSpace(req.Input)
+	if len(inputRaw) == 0 || string(inputRaw) == "null" || inputRaw[0] != '[' {
+		return tools, nil
+	}
+
+	var items []json.RawMessage
+	if err := json.Unmarshal(inputRaw, &items); err != nil {
+		return nil, fmt.Errorf("parse responses input for additional tools: %w", err)
+	}
+	for _, raw := range items {
+		raw = bytesTrimSpace(raw)
+		if len(raw) == 0 || raw[0] != '{' {
+			continue
+		}
+		var item struct {
+			Type  string          `json:"type"`
+			Tools []ResponsesTool `json:"tools"`
+		}
+		if err := json.Unmarshal(raw, &item); err != nil {
+			return nil, fmt.Errorf("parse responses additional tools item: %w", err)
+		}
+		if item.Type == "additional_tools" {
+			tools = append(tools, item.Tools...)
+		}
+	}
+	return tools, nil
+}
+
 // CustomToolNames 收集 Responses 请求中 custom/freeform 工具的名字。chat 桥回程时
 // 需要据此把模型对这些工具的调用还原为 custom_tool_call 项（codex 只按该类型路由）。
 func CustomToolNames(tools []ResponsesTool) map[string]bool {
diff --git a/backend/internal/pkg/apicompat/chatcompletions_responses_bridge_custom_tools_test.go b/backend/internal/pkg/apicompat/chatcompletions_responses_bridge_custom_tools_test.go
index 9271b50d1d..5b1d994eb3 100644
--- a/backend/internal/pkg/apicompat/chatcompletions_responses_bridge_custom_tools_test.go
+++ b/backend/internal/pkg/apicompat/chatcompletions_responses_bridge_custom_tools_test.go
@@ -34,6 +34,51 @@ func TestResponsesToChatCompletionsRequest_CustomToolBecomesFunctionTool(t *test
 	assert.Equal(t, "wait", out.Tools[1].Function.Name)
 }
 
+func TestResponsesToChatCompletionsRequest_AdditionalToolsItem(t *testing.T) {
+	req := &ResponsesRequest{
+		Model: "gpt-test",
+		Input: json.RawMessage(`[
+			{"type":"additional_tools","role":"developer","tools":[
+				{"type":"custom","name":"exec","description":"Run PowerShell","format":{"type":"text"}},
+				{"type":"function","name":"wait","parameters":{"type":"object","properties":{}}},
+				{"type":"namespace","name":"collaboration","tools":[
+					{"type":"function","name":"send_message","parameters":{"type":"object","properties":{}}}
+				]}
+			]},
+			{"type":"message","role":"user","content":[{"type":"input_text","text":"run Get-Location"}]}
+		]`),
+		ToolChoice: json.RawMessage(`"auto"`),
+	}
+
+	effective, err := EffectiveResponsesTools(req)
+	require.NoError(t, err)
+	require.Len(t, effective, 3)
+	assert.True(t, CustomToolNames(effective)["exec"])
+	assert.Equal(t, NamespacedToolName{Namespace: "collaboration", Name: "send_message"}, NamespaceToolNames(effective)["collaboration__send_message"])
+
+	out, err := ResponsesToChatCompletionsRequest(req)
+	require.NoError(t, err)
+	require.Len(t, out.Tools, 3)
+	assert.Equal(t, "exec", out.Tools[0].Function.Name)
+	assert.Equal(t, "wait", out.Tools[1].Function.Name)
+	assert.Equal(t, "collaboration__send_message", out.Tools[2].Function.Name)
+	assert.JSONEq(t, `"auto"`, string(out.ToolChoice))
+
+	require.Len(t, out.Messages, 1, "additional_tools must not become a chat message")
+	assert.Equal(t, "user", out.Messages[0].Role)
+}
+
+func TestEffectiveResponsesTools_SkipsStringInputItems(t *testing.T) {
+	req := &ResponsesRequest{
+		Input: json.RawMessage(`["plain input",{"type":"additional_tools","tools":[{"type":"custom","name":"exec"}]}]`),
+	}
+
+	tools, err := EffectiveResponsesTools(req)
+	require.NoError(t, err)
+	require.Len(t, tools, 1)
+	assert.Equal(t, "exec", tools[0].Name)
+}
+
 func TestResponsesToChatCompletionsRequest_DropsToolChoiceWhenNoConvertibleTools(t *testing.T) {
 	req := &ResponsesRequest{
 		Model: "glm-5.2",
diff --git a/backend/internal/service/openai_gateway_responses_chat_fallback.go b/backend/internal/service/openai_gateway_responses_chat_fallback.go
index f494429226..1082b020dd 100644
--- a/backend/internal/service/openai_gateway_responses_chat_fallback.go
+++ b/backend/internal/service/openai_gateway_responses_chat_fallback.go
@@ -43,9 +43,14 @@ func (s *OpenAIGatewayService) forwardResponsesViaRawChatCompletions(
 	// custom_tool_call 项，先记下名字集合；tool_search 工具同理，回程还原为
 	// tool_search_call 项；namespace 子工具（如 MCP 工具）摊平转发，回程按映射还原
 	// 为带 namespace 字段的 function_call 项。
-	customTools := apicompat.CustomToolNames(responsesReq.Tools)
-	toolSearch := apicompat.HasToolSearchTool(responsesReq.Tools)
-	namespaceTools := apicompat.NamespaceToolNames(responsesReq.Tools)
+	effectiveTools, err := apicompat.EffectiveResponsesTools(&responsesReq)
+	if err != nil {
+		writeOpenAIResponsesFallbackError(c, http.StatusBadRequest, "invalid_request_error", err.Error())
+		return nil, fmt.Errorf("resolve responses tools: %w", err)
+	}
+	customTools := apicompat.CustomToolNames(effectiveTools)
+	toolSearch := apicompat.HasToolSearchTool(effectiveTools)
+	namespaceTools := apicompat.NamespaceToolNames(effectiveTools)
 
 	chatReq, err := apicompat.ResponsesToChatCompletionsRequest(&responsesReq)
 	if err != nil {