diff --git a/sdk/api/handlers/openai/openai_responses_websocket.go b/sdk/api/handlers/openai/openai_responses_websocket.go
index eae042b9e..142719aa2 100644
--- a/sdk/api/handlers/openai/openai_responses_websocket.go
+++ b/sdk/api/handlers/openai/openai_responses_websocket.go
@@ -381,6 +381,7 @@ func (h *OpenAIResponsesAPIHandler) ResponsesWebsocket(c *gin.Context) {
 		}
 
 		requestJSON = repairResponsesWebsocketToolCalls(downstreamSessionKey, requestJSON)
+		requestJSON = dedupeResponsesWebsocketInputItemsByID(requestJSON)
 		updatedLastRequest = bytes.Clone(requestJSON)
 		previousLastRequest := bytes.Clone(lastRequest)
 		previousLastResponseOutput := bytes.Clone(lastResponseOutput)
@@ -582,6 +583,10 @@ func normalizeResponseSubsequentRequest(rawJSON []byte, lastRequest []byte, last
 	if errDedupeFunctionCalls == nil {
 		mergedInput = dedupedInput
 	}
+	dedupedInput, errDedupeItemIDs := dedupeInputItemsByID(mergedInput)
+	if errDedupeItemIDs == nil {
+		mergedInput = dedupedInput
+	}
 
 	normalized, errDelete := sjson.DeleteBytes(rawJSON, "type")
 	if errDelete != nil {
@@ -697,6 +702,64 @@ func dedupeFunctionCallsByCallID(rawArray string) (string, error) {
 	return string(out), nil
 }
 
+func dedupeResponsesWebsocketInputItemsByID(payload []byte) []byte {
+	input := gjson.GetBytes(payload, "input")
+	if !input.Exists() || !input.IsArray() {
+		return payload
+	}
+	dedupedInput, errDedupe := dedupeInputItemsByID(input.Raw)
+	if errDedupe != nil || dedupedInput == input.Raw {
+		return payload
+	}
+	updated, errSet := sjson.SetRawBytes(payload, "input", []byte(dedupedInput))
+	if errSet != nil {
+		return payload
+	}
+	return updated
+}
+
+func dedupeInputItemsByID(rawArray string) (string, error) {
+	rawArray = strings.TrimSpace(rawArray)
+	if rawArray == "" {
+		return "[]", nil
+	}
+	var items []json.RawMessage
+	if errUnmarshal := json.Unmarshal([]byte(rawArray), &items); errUnmarshal != nil {
+		return "", errUnmarshal
+	}
+
+	lastIndexByID := make(map[string]int, len(items))
+	for i, item := range items {
+		if len(item) == 0 {
+			continue
+		}
+		itemID := strings.TrimSpace(gjson.GetBytes(item, "id").String())
+		if itemID != "" {
+			lastIndexByID[itemID] = i
+		}
+	}
+
+	filtered := make([]json.RawMessage, 0, len(items))
+	for i, item := range items {
+		if len(item) == 0 {
+			continue
+		}
+		itemID := strings.TrimSpace(gjson.GetBytes(item, "id").String())
+		if itemID != "" {
+			if lastIndexByID[itemID] != i {
+				continue
+			}
+		}
+		filtered = append(filtered, item)
+	}
+
+	out, errMarshal := json.Marshal(filtered)
+	if errMarshal != nil {
+		return "", errMarshal
+	}
+	return string(out), nil
+}
+
 func websocketUpstreamSupportsIncrementalInput(attributes map[string]string, metadata map[string]any) bool {
 	if len(attributes) > 0 {
 		if raw := strings.TrimSpace(attributes["websockets"]); raw != "" {
diff --git a/sdk/api/handlers/openai/openai_responses_websocket_test.go b/sdk/api/handlers/openai/openai_responses_websocket_test.go
index d37c783db..9f23af82d 100644
--- a/sdk/api/handlers/openai/openai_responses_websocket_test.go
+++ b/sdk/api/handlers/openai/openai_responses_websocket_test.go
@@ -1603,6 +1603,30 @@ func TestNormalizeResponsesWebsocketRequestDropsDuplicateFunctionCallsByCallID(t
 	}
 }
 
+func TestNormalizeResponsesWebsocketRequestDropsDuplicateInputItemsByID(t *testing.T) {
+	lastRequest := []byte(`{"model":"test-model","stream":true,"input":[{"type":"message","id":"msg-1","role":"user"}]}`)
+	lastResponseOutput := []byte(`[
+		{"type":"function_call","id":"fc-1","call_id":"call-1","name":"tool"}
+	]`)
+	raw := []byte(`{"type":"response.create","previous_response_id":"resp-1","input":[{"type":"function_call","id":"fc-1","call_id":"call-2","name":"tool"},{"type":"function_call_output","id":"tool-out-1","call_id":"call-2"}]}`)
+
+	normalized, _, errMsg := normalizeResponsesWebsocketRequestWithMode(raw, lastRequest, lastResponseOutput, false, true)
+	if errMsg != nil {
+		t.Fatalf("unexpected error: %v", errMsg.Error)
+	}
+
+	items := gjson.GetBytes(normalized, "input").Array()
+	if len(items) != 3 {
+		t.Fatalf("merged input len = %d, want 3: %s", len(items), normalized)
+	}
+	if items[0].Get("id").String() != "msg-1" ||
+		items[1].Get("id").String() != "fc-1" ||
+		items[1].Get("call_id").String() != "call-2" ||
+		items[2].Get("id").String() != "tool-out-1" {
+		t.Fatalf("unexpected merged input order: %s", normalized)
+	}
+}
+
 func TestNormalizeResponsesWebsocketRequestTreatsCustomToolTranscriptReplacementAsReset(t *testing.T) {
 	lastRequest := []byte(`{"model":"test-model","stream":true,"input":[{"type":"message","id":"msg-1"},{"type":"custom_tool_call","id":"ctc-1","call_id":"call-1","name":"apply_patch"},{"type":"custom_tool_call_output","id":"tool-out-1","call_id":"call-1"},{"type":"message","id":"assistant-1","role":"assistant"}]}`)
 	lastResponseOutput := []byte(`[
@@ -1654,6 +1678,22 @@ func TestNormalizeResponsesWebsocketRequestDropsDuplicateCustomToolCallsByCallID
 	}
 }
 
+func TestDedupeResponsesWebsocketInputItemsByIDAfterRepair(t *testing.T) {
+	payload := []byte(`{"input":[{"type":"custom_tool_call","id":"ctc-1","call_id":"call-1","name":"tool"},{"type":"custom_tool_call","id":"ctc-1","call_id":"call-2","name":"tool"},{"type":"custom_tool_call_output","id":"tool-out-1","call_id":"call-2"}]}`)
+
+	deduped := dedupeResponsesWebsocketInputItemsByID(payload)
+
+	items := gjson.GetBytes(deduped, "input").Array()
+	if len(items) != 2 {
+		t.Fatalf("deduped input len = %d, want 2: %s", len(items), deduped)
+	}
+	if items[0].Get("id").String() != "ctc-1" ||
+		items[0].Get("call_id").String() != "call-2" ||
+		items[1].Get("id").String() != "tool-out-1" {
+		t.Fatalf("unexpected deduped input: %s", deduped)
+	}
+}
+
 func TestResponsesWebsocketCompactionResetsTurnStateOnCustomToolTranscriptReplacement(t *testing.T) {
 	gin.SetMode(gin.TestMode)