diff --git a/backend/internal/service/openai_gateway_grok.go b/backend/internal/service/openai_gateway_grok.go
index c67a3b9919..20640daf65 100644
--- a/backend/internal/service/openai_gateway_grok.go
+++ b/backend/internal/service/openai_gateway_grok.go
@@ -1159,8 +1159,7 @@ func sanitizeGrokResponsesTools(body []byte) ([]byte, error) {
 }
 
 func grokFunctionParametersHaveInvalidUnionRoot(parameters gjson.Result) bool {
-	if !parameters.Exists() || !parameters.IsObject() ||
-		strings.EqualFold(strings.TrimSpace(parameters.Get("type").String()), "object") {
+	if !parameters.Exists() || !parameters.IsObject() {
 		return false
 	}
 	for _, keyword := range []string{"anyOf", "oneOf"} {
diff --git a/backend/internal/service/openai_gateway_grok_test.go b/backend/internal/service/openai_gateway_grok_test.go
index b01c14c782..d3256eac93 100644
--- a/backend/internal/service/openai_gateway_grok_test.go
+++ b/backend/internal/service/openai_gateway_grok_test.go
@@ -398,7 +398,7 @@ func TestSanitizeGrokResponsesToolsRemovesDeferredFlagsWithToolSearch(t *testing
 func TestSanitizeGrokResponsesToolsSimplifiesInvalidRootUnion(t *testing.T) {
 	body := []byte(`{"tools":[
 		{"type":"function","name":"mcp__codex_app__automation_update","strict":true,"parameters":{"oneOf":[{"type":"object","properties":{"id":{"type":"string"}}},{"type":"null"}]}},
-		{"type":"function","name":"object_only","strict":true,"parameters":{"anyOf":[{"type":"object","properties":{"a":{"type":"string"}}},{"type":"object","properties":{"b":{"type":"integer"}}}]}}
+		{"type":"function","name":"object_only","strict":true,"parameters":{"type":"object","anyOf":[{"type":"object","properties":{"a":{"type":"string"}}},{"type":"object","properties":{"b":{"type":"integer"}}}]}}
 	]}`)
 
 	patched, err := sanitizeGrokResponsesTools(body)
@@ -417,6 +417,40 @@ func TestSanitizeGrokResponsesToolsSimplifiesInvalidRootUnion(t *testing.T) {
 	require.Equal(t, gjson.True, objectOnly.Get("strict").Type)
 }
 
+func TestPatchGrokResponsesBodySimplifiesTypedInvalidRootUnion(t *testing.T) {
+	body := []byte(`{
+		"model":"grok-4.6",
+		"metadata":{"session_id":"abc"},
+		"tools":[{
+			"type":"namespace",
+			"name":"mcp__codex_app",
+			"tools":[{
+				"type":"function",
+				"name":"automation_update",
+				"strict":true,
+				"parameters":{
+					"type":"object",
+					"oneOf":[{"$ref":"#/$defs/update"},{"type":"null"}],
+					"$defs":{"update":{"type":"object","properties":{"id":{"type":"string"}}}}
+				}
+			}]
+		}]
+	}`)
+
+	patched, _, err := patchGrokResponsesBodyWithClientTools(body, "grok-4.6")
+	require.NoError(t, err)
+	require.True(t, json.Valid(patched))
+	require.False(t, gjson.GetBytes(patched, "metadata").Exists())
+
+	tool := gjson.GetBytes(patched, `tools.#(name=="mcp__codex_app__automation_update")`)
+	require.Equal(t, "object", tool.Get("parameters.type").String())
+	require.True(t, tool.Get("parameters.properties").IsObject())
+	require.True(t, tool.Get("parameters.additionalProperties").Bool())
+	require.False(t, tool.Get("parameters.oneOf").Exists())
+	require.False(t, tool.Get("parameters.$defs").Exists())
+	require.Equal(t, gjson.False, tool.Get("strict").Type)
+}
+
 func TestSanitizeGrokResponsesToolsKeepsToolChoiceOnlyWithSupportedTools(t *testing.T) {
 	t.Parallel()