diff --git a/backend/internal/service/openai_gateway_forward.go b/backend/internal/service/openai_gateway_forward.go
index 6487385000..ebf12675c9 100644
--- a/backend/internal/service/openai_gateway_forward.go
+++ b/backend/internal/service/openai_gateway_forward.go
@@ -173,6 +173,17 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 		return s.forwardResponsesViaRawChatCompletions(ctx, c, account, body)
 	}
 	if account.IsOpenAI() && (account.IsOpenAIApiKey() || account.IsOpenAIOAuthLike()) {
+		normalizedReasoningBody, reasoningChanged, reasoningErr := normalizeOpenAIResponsesReasoningContentReplay(body)
+		if reasoningErr != nil {
+			return nil, fmt.Errorf("normalize OpenAI Responses reasoning content replay: %w", reasoningErr)
+		}
+		if reasoningChanged {
+			body = normalizedReasoningBody
+			originalBody = normalizedReasoningBody
+			requestView = newOpenAIRequestView(normalizedReasoningBody)
+			reqModel, reqStream, promptCacheKey = requestView.Model, requestView.Stream, requestView.PromptCacheKey
+			originalModel = reqModel
+		}
 		sanitizedBody, changed, sanitizeErr := sanitizeOpenAIResponsesInputItemIDs(body)
 		if sanitizeErr != nil {
 			return nil, fmt.Errorf("sanitize OpenAI Responses input item IDs: %w", sanitizeErr)
diff --git a/backend/internal/service/openai_gateway_request_body.go b/backend/internal/service/openai_gateway_request_body.go
index 6272875cc5..23cc01d670 100644
--- a/backend/internal/service/openai_gateway_request_body.go
+++ b/backend/internal/service/openai_gateway_request_body.go
@@ -395,6 +395,67 @@ func openAIRequestBodyHasTools(body []byte) bool {
 	return false
 }
 
+// normalizeOpenAIResponsesReasoningContentReplay removes non-portable
+// reasoning.content arrays before history is sent to a real OpenAI Responses
+// endpoint. Compatible providers may return visible reasoning blocks there,
+// while OpenAI accepts only an empty array when the item is replayed.
+//
+// Keep the reasoning item and its portable fields (summary, encrypted_content,
+// ids, and opaque extensions). Callers scope this normalization to OpenAI
+// destinations; compatible providers may still consume their own content.
+func normalizeOpenAIResponsesReasoningContentReplay(body []byte) ([]byte, bool, error) {
+	input := gjson.GetBytes(body, "input")
+	if !input.IsArray() {
+		return body, false, nil
+	}
+
+	needsNormalization := false
+	input.ForEach(func(_, item gjson.Result) bool {
+		if strings.TrimSpace(item.Get("type").String()) != "reasoning" {
+			return true
+		}
+		content := item.Get("content")
+		if content.IsArray() && len(content.Array()) > 0 {
+			needsNormalization = true
+			return false
+		}
+		return true
+	})
+	if !needsNormalization {
+		return body, false, nil
+	}
+
+	var reqBody map[string]any
+	if err := decodeOpenAIJSONUseNumber(body, &reqBody); err != nil {
+		return body, false, fmt.Errorf("normalize OpenAI reasoning content replay: %w", err)
+	}
+	items, ok := reqBody["input"].([]any)
+	if !ok {
+		return body, false, nil
+	}
+	changed := false
+	for _, rawItem := range items {
+		item, ok := rawItem.(map[string]any)
+		if !ok || strings.TrimSpace(firstNonEmptyString(item["type"])) != "reasoning" {
+			continue
+		}
+		content, ok := item["content"].([]any)
+		if !ok || len(content) == 0 {
+			continue
+		}
+		delete(item, "content")
+		changed = true
+	}
+	if !changed {
+		return body, false, nil
+	}
+	normalized, err := marshalOpenAIUpstreamJSON(reqBody)
+	if err != nil {
+		return body, false, fmt.Errorf("serialize normalized OpenAI reasoning content replay: %w", err)
+	}
+	return normalized, true, nil
+}
+
 func normalizeOpenAIAPIKeyStoreFalseReasoningReplay(body []byte, knownStoreFalse bool) ([]byte, bool, error) {
 	if !knownStoreFalse && gjson.GetBytes(body, "store").Type != gjson.False {
 		return body, false, nil
@@ -955,6 +1016,12 @@ func normalizeOpenAIResponsesWebSocketCompatibilityBody(body []byte, account *Ac
 			return body, false, err
 		}
 	}
+	if next, normalizedReasoningContent, err := normalizeOpenAIResponsesReasoningContentReplay(normalized); err != nil {
+		return body, false, err
+	} else if normalizedReasoningContent {
+		normalized = next
+		changed = true
+	}
 	if account.IsOpenAIApiKey() {
 		if next, normalizedParallel, err := normalizeOpenAIParallelToolCallsWithoutTools(normalized, responsesLite); err != nil {
 			return body, false, err
diff --git a/backend/internal/service/openai_gateway_request_body_reasoning_test.go b/backend/internal/service/openai_gateway_request_body_reasoning_test.go
index 543d294880..cbe24815cd 100644
--- a/backend/internal/service/openai_gateway_request_body_reasoning_test.go
+++ b/backend/internal/service/openai_gateway_request_body_reasoning_test.go
@@ -293,3 +293,60 @@ func TestNormalizeOpenAIParallelToolCallsWithoutTools_KeepsResponsesLiteAddition
 	require.False(t, changed)
 	require.Equal(t, gjson.False, gjson.GetBytes(normalized, "parallel_tool_calls").Type)
 }
+
+func TestNormalizeOpenAIResponsesReasoningContentReplayStripsCrossProviderArray(t *testing.T) {
+	body := []byte(`{"model":"gpt-5.6-sol","input":[` +
+		`{"type":"message","role":"user","content":"one"},` +
+		`{"type":"message","role":"assistant","content":"two"},` +
+		`{"type":"function_call","call_id":"call_1","name":"lookup","arguments":"{}"},` +
+		`{"type":"function_call_output","call_id":"call_1","output":"ok"},` +
+		`{"type":"message","role":"user","content":"five"},` +
+		`{"type":"reasoning","id":"rs_provider","summary":[{"type":"summary_text","text":"portable"}],"content":[{"type":"reasoning_text","text":"visible reasoning"}],"opaque":9007199254740993},` +
+		`{"type":"message","role":"assistant","content":[{"type":"output_text","text":"answer"}]}` +
+		`]}`)
+
+	normalized, changed, err := normalizeOpenAIResponsesReasoningContentReplay(body)
+
+	require.NoError(t, err)
+	require.True(t, changed)
+	require.Equal(t, "reasoning", gjson.GetBytes(normalized, "input.5.type").String())
+	require.False(t, gjson.GetBytes(normalized, "input.5.content").Exists())
+	require.Equal(t, "portable", gjson.GetBytes(normalized, "input.5.summary.0.text").String())
+	require.Equal(t, "9007199254740993", gjson.GetBytes(normalized, "input.5.opaque").Raw)
+	require.Equal(t, "answer", gjson.GetBytes(normalized, "input.6.content.0.text").String())
+}
+
+func TestNormalizeOpenAIResponsesReasoningContentReplayKeepsPortableShapes(t *testing.T) {
+	for _, body := range []string{
+		`{"input":[{"type":"reasoning","summary":[]}]}`,
+		`{"input":[{"type":"reasoning","content":[],"summary":[]}]}`,
+		`{"input":[{"type":"message","content":[{"type":"input_text","text":"keep"}]}]}`,
+	} {
+		normalized, changed, err := normalizeOpenAIResponsesReasoningContentReplay([]byte(body))
+		require.NoError(t, err)
+		require.False(t, changed)
+		require.JSONEq(t, body, string(normalized))
+	}
+}
+
+func TestNormalizeOpenAIResponsesWebSocketCompatibilityBodyStripsReasoningContentOnlyForOpenAI(t *testing.T) {
+	body := []byte(`{"type":"response.create","model":"gpt-5.6-sol","store":true,"input":[{"type":"reasoning","summary":[{"type":"summary_text","text":"keep"}],"content":[{"type":"reasoning_text","text":"remove"}]}]}`)
+	for _, accountType := range []string{AccountTypeAPIKey, AccountTypeOAuth} {
+		normalized, changed, err := normalizeOpenAIResponsesWebSocketCompatibilityBody(body, &Account{
+			Platform: PlatformOpenAI,
+			Type:     accountType,
+		}, false)
+		require.NoError(t, err)
+		require.True(t, changed)
+		require.False(t, gjson.GetBytes(normalized, "input.0.content").Exists())
+		require.Equal(t, "keep", gjson.GetBytes(normalized, "input.0.summary.0.text").String())
+	}
+
+	normalized, changed, err := normalizeOpenAIResponsesWebSocketCompatibilityBody(body, &Account{
+		Platform: PlatformZhipu,
+		Type:     AccountTypeAPIKey,
+	}, false)
+	require.NoError(t, err)
+	require.False(t, changed)
+	require.JSONEq(t, string(body), string(normalized))
+}
diff --git a/backend/internal/service/openai_responses_rejected_field_retry_test.go b/backend/internal/service/openai_responses_rejected_field_retry_test.go
index 9f794b1e57..4ed3e3ba22 100644
--- a/backend/internal/service/openai_responses_rejected_field_retry_test.go
+++ b/backend/internal/service/openai_responses_rejected_field_retry_test.go
@@ -538,6 +538,34 @@ func TestOpenAIGatewayService_APIKeyStripsAllIndexedNamespacesBeforeFirstForward
 	require.False(t, gjson.GetBytes(upstream.bodies[0], "input.1.namespace").Exists())
 }
 
+func TestOpenAIGatewayServiceProactivelyStripsCrossProviderReasoningContent(t *testing.T) {
+	body := []byte(`{"model":"gpt-5.5","stream":false,"store":true,"input":[` +
+		`{"type":"message","role":"user","content":"one"},` +
+		`{"type":"message","role":"assistant","content":"two"},` +
+		`{"type":"function_call","call_id":"call_1","name":"lookup","arguments":"{}"},` +
+		`{"type":"function_call_output","call_id":"call_1","output":"ok"},` +
+		`{"type":"message","role":"user","content":"five"},` +
+		`{"type":"reasoning","summary":[{"type":"summary_text","text":"keep"}],"content":[{"type":"reasoning_text","text":"remove"}]}` +
+		`]}`)
+	upstream := &httpUpstreamRecorder{responses: []*http.Response{
+		newOpenAIRejectedFieldTestResponse(http.StatusOK, `{"output":[],"usage":{"input_tokens":1,"output_tokens":1,"input_tokens_details":{"cached_tokens":0}}}`),
+	}}
+
+	result, err := newOpenAIRejectedFieldTestService(upstream).Forward(
+		context.Background(),
+		newOpenAIRejectedFieldTestContext(body),
+		newOpenAIRejectedFieldTestAccount(),
+		body,
+	)
+
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Len(t, upstream.bodies, 1, "reasoning content should be normalized before the first upstream request")
+	require.Equal(t, "reasoning", gjson.GetBytes(upstream.bodies[0], "input.5.type").String())
+	require.False(t, gjson.GetBytes(upstream.bodies[0], "input.5.content").Exists())
+	require.Equal(t, "keep", gjson.GetBytes(upstream.bodies[0], "input.5.summary.0.text").String())
+}
+
 func TestOpenAIGatewayService_OpenAIHTTPStripsInputNamespacesBeforeFirstForward(t *testing.T) {
 	accounts := []struct {
 		name    string