diff --git a/backend/internal/service/openai_gateway_request_body.go b/backend/internal/service/openai_gateway_request_body.go
index 46f69b54d6..9dd1654727 100644
--- a/backend/internal/service/openai_gateway_request_body.go
+++ b/backend/internal/service/openai_gateway_request_body.go
@@ -59,6 +59,9 @@ func shouldPreserveOpenAIResponsesNoneReasoningEffort(account *Account) bool {
 	if account == nil {
 		return false
 	}
+	if account.IsOpenAIPassthroughEnabled() {
+		return true
+	}
 	if account.IsOpenAIOAuthLike() {
 		return true
 	}
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 4805eeeb24..013aaa2531 100644
--- a/backend/internal/service/openai_gateway_request_body_reasoning_test.go
+++ b/backend/internal/service/openai_gateway_request_body_reasoning_test.go
@@ -331,6 +331,23 @@ func TestFilterOpenAIResponsesNoneReasoningEffortForAccount(t *testing.T) {
 	}
 }
 
+func TestFilterOpenAIResponsesNoneReasoningEffortForAccount_APIKeyAutomaticPassthroughPreservesRequest(t *testing.T) {
+	body := []byte(`{"model":"qwen3.8-27b","input":"hi","max_output_tokens":20,"reasoning":{"effort":"none"},"presence_penalty":1.5}`)
+	account := &Account{
+		Platform: PlatformOpenAI,
+		Type:     AccountTypeAPIKey,
+		Credentials: map[string]any{
+			"base_url": "https://compat.example/v1",
+		},
+		Extra: map[string]any{"openai_passthrough": true},
+	}
+
+	got, err := filterOpenAIResponsesNoneReasoningEffortForAccount(account, body)
+
+	require.NoError(t, err)
+	require.JSONEq(t, string(body), string(got))
+}
+
 // Lite 工具迁移到 input[].additional_tools 后，仍应按有工具请求处理。
 func TestNormalizeOpenAIParallelToolCallsWithoutTools_KeepsResponsesLiteAdditionalTools(t *testing.T) {
 	liteBody := []byte(`{"input":[{"type":"message","role":"user","content":"hi"},{"type":"additional_tools","tools":[{"type":"function","name":"spawn_agent"}]}],"parallel_tool_calls":false}`)