diff --git a/backend/internal/service/openai_codex_transform.go b/backend/internal/service/openai_codex_transform.go
index 1bc7390a..b256f1c7 100644
--- a/backend/internal/service/openai_codex_transform.go
+++ b/backend/internal/service/openai_codex_transform.go
@@ -53,6 +53,23 @@ const (
 	codexSparkImageUnsupportedText   = codexSparkImageUnsupportedMarker + "\nThe current model is gpt-5.3-codex-spark, which does not support image generation, image editing, image input, the `image_generation` tool, or Codex `image_gen`/`$imagegen` workflows. If the user asks for image generation or image editing, clearly explain this model limitation and ask them to switch to a non-Spark Codex model such as gpt-5.3-codex or gpt-5.4. Do not claim that the local environment merely lacks image_gen tooling, and do not suggest CLI fallback as the primary fix while the model remains Spark.\n</sub2api-codex-spark-image-unsupported>"
 )
 
+var openAIChatGPTInternalUnsupportedFields = []string{
+	"user",
+	"metadata",
+	"prompt_cache_retention",
+	"safety_identifier",
+	"stream_options",
+}
+
+var openAICodexOAuthUnsupportedFields = append([]string{
+	"max_output_tokens",
+	"max_completion_tokens",
+	"temperature",
+	"top_p",
+	"frequency_penalty",
+	"presence_penalty",
+}, openAIChatGPTInternalUnsupportedFields...)
+
 func applyCodexOAuthTransform(reqBody map[string]any, isCodexCLI bool, isCompact bool) codexTransformResult {
 	result := codexTransformResult{}
 	// 工具续链需求会影响存储策略与 input 过滤逻辑。
@@ -93,23 +110,8 @@ func applyCodexOAuthTransform(reqBody map[string]any, isCodexCLI bool, isCompact
 		}
 	}
 
-	// Strip parameters unsupported by codex models via the Responses API.
-	for _, key := range []string{
-		"max_output_tokens",
-		"max_completion_tokens",
-		"temperature",
-		"top_p",
-		"frequency_penalty",
-		"presence_penalty",
-		// prompt_cache_retention is a newer Responses API parameter (cache TTL).
-		// The ChatGPT internal Codex endpoint rejects it with
-		// "Unsupported parameter: prompt_cache_retention". Defense-in-depth
-		// for any OAuth path that reaches this transform — the Cursor
-		// Responses-shape short-circuit in ForwardAsChatCompletions strips
-		// it earlier too, but we keep this line so other OAuth callers are
-		// equally protected.
-		"prompt_cache_retention",
-	} {
+	// Strip parameters unsupported by ChatGPT internal Codex endpoint.
+	for _, key := range openAICodexOAuthUnsupportedFields {
 		if _, ok := reqBody[key]; ok {
 			delete(reqBody, key)
 			result.Modified = true
diff --git a/backend/internal/service/openai_codex_transform_test.go b/backend/internal/service/openai_codex_transform_test.go
index 7ab6bfc0..87bb7162 100644
--- a/backend/internal/service/openai_codex_transform_test.go
+++ b/backend/internal/service/openai_codex_transform_test.go
@@ -1088,6 +1088,27 @@ func TestApplyCodexOAuthTransform_StripsPromptCacheRetention(t *testing.T) {
 		"prompt_cache_retention must be stripped before forwarding to Codex upstream")
 }
 
+func TestApplyCodexOAuthTransform_StripsChatGPTInternalUnsupportedFields(t *testing.T) {
+	reqBody := map[string]any{
+		"model":                  "gpt-5.4",
+		"user":                   "user_123",
+		"metadata":               map[string]any{"trace_id": "abc"},
+		"prompt_cache_retention": "24h",
+		"safety_identifier":      "sid",
+		"stream_options":         map[string]any{"include_usage": true},
+		"input": []any{
+			map[string]any{"role": "user", "content": "hi"},
+		},
+	}
+
+	result := applyCodexOAuthTransform(reqBody, true, false)
+
+	require.True(t, result.Modified)
+	for _, field := range openAIChatGPTInternalUnsupportedFields {
+		require.NotContains(t, reqBody, field)
+	}
+}
+
 func TestApplyCodexOAuthTransform_ExtractsSystemMessages(t *testing.T) {
 	reqBody := map[string]any{
 		"model": "gpt-5.1",
diff --git a/backend/internal/service/openai_gateway_service.go b/backend/internal/service/openai_gateway_service.go
index 4113e789..ed69730c 100644
--- a/backend/internal/service/openai_gateway_service.go
+++ b/backend/internal/service/openai_gateway_service.go
@@ -5553,7 +5553,8 @@ func extractOpenAIRequestMetaFromBody(body []byte) (model string, stream bool, p
 }
 
 // normalizeOpenAIPassthroughOAuthBody 将透传 OAuth 请求体收敛为旧链路关键行为：
-// 1) store=false 2) 非 compact 保持 stream=true；compact 强制 stream=false
+// 1) 删除 ChatGPT internal API 不支持的顶层 Responses 参数
+// 2) store=false 3) 非 compact 保持 stream=true；compact 强制 stream=false
 func normalizeOpenAIPassthroughOAuthBody(body []byte, compact bool) ([]byte, bool, error) {
 	if len(body) == 0 {
 		return body, false, nil
@@ -5562,6 +5563,18 @@ func normalizeOpenAIPassthroughOAuthBody(body []byte, compact bool) ([]byte, boo
 	normalized := body
 	changed := false
 
+	for _, field := range openAIChatGPTInternalUnsupportedFields {
+		if value := gjson.GetBytes(normalized, field); !value.Exists() {
+			continue
+		}
+		next, err := sjson.DeleteBytes(normalized, field)
+		if err != nil {
+			return body, false, fmt.Errorf("normalize passthrough body delete %s: %w", field, err)
+		}
+		normalized = next
+		changed = true
+	}
+
 	if compact {
 		if store := gjson.GetBytes(normalized, "store"); store.Exists() {
 			next, err := sjson.DeleteBytes(normalized, "store")
diff --git a/backend/internal/service/openai_passthrough_normalization_test.go b/backend/internal/service/openai_passthrough_normalization_test.go
new file mode 100644
index 00000000..492ff610
--- /dev/null
+++ b/backend/internal/service/openai_passthrough_normalization_test.go
@@ -0,0 +1,33 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
+)
+
+func TestNormalizeOpenAIPassthroughOAuthBody_RemovesUnsupportedUser(t *testing.T) {
+	body := []byte(`{"model":"gpt-5.4","input":"hello","user":"user_123","metadata":{"user_id":"user_123"},"prompt_cache_retention":"24h","safety_identifier":"sid","stream_options":{"include_usage":true}}`)
+
+	normalized, changed, err := normalizeOpenAIPassthroughOAuthBody(body, false)
+	require.NoError(t, err)
+	require.True(t, changed)
+	for _, field := range openAIChatGPTInternalUnsupportedFields {
+		require.False(t, gjson.GetBytes(normalized, field).Exists(), "%s should be stripped", field)
+	}
+	require.True(t, gjson.GetBytes(normalized, "stream").Bool())
+	require.False(t, gjson.GetBytes(normalized, "store").Bool())
+}
+
+func TestNormalizeOpenAIPassthroughOAuthBody_CompactRemovesUnsupportedUser(t *testing.T) {
+	body := []byte(`{"model":"gpt-5.4","input":"hello","user":"user_123","metadata":{"user_id":"user_123"},"stream":true,"store":true}`)
+
+	normalized, changed, err := normalizeOpenAIPassthroughOAuthBody(body, true)
+	require.NoError(t, err)
+	require.True(t, changed)
+	require.False(t, gjson.GetBytes(normalized, "user").Exists())
+	require.False(t, gjson.GetBytes(normalized, "metadata").Exists())
+	require.False(t, gjson.GetBytes(normalized, "stream").Exists())
+	require.False(t, gjson.GetBytes(normalized, "store").Exists())
+}