diff --git a/internal/runtime/executor/antigravity_executor.go b/internal/runtime/executor/antigravity_executor.go
index 4796fa9a5..4430f27d4 100644
--- a/internal/runtime/executor/antigravity_executor.go
+++ b/internal/runtime/executor/antigravity_executor.go
@@ -1946,17 +1946,46 @@ func (e *AntigravityExecutor) buildRequest(ctx context.Context, auth *cliproxyau
 	payload, _ = sjson.SetBytes(payload, "model", modelName)
 
 	useAntigravitySchema := strings.Contains(modelName, "claude") || strings.Contains(modelName, "gemini-3-pro") || strings.Contains(modelName, "gemini-3.1-pro")
-	payloadStr := string(payload)
-	paths := make([]string, 0)
-	util.Walk(gjson.Parse(payloadStr), "", "parametersJsonSchema", &paths)
-	for _, p := range paths {
-		payloadStr, _ = util.RenameKey(payloadStr, p, p[:len(p)-len("parametersJsonSchema")]+"parameters")
-	}
+	var (
+		bodyReader io.Reader
+		payloadLog []byte
+	)
+	if antigravityRequestNeedsSchemaSanitization(payload) {
+		payloadStr := string(payload)
+		paths := make([]string, 0)
+		util.Walk(gjson.Parse(payloadStr), "", "parametersJsonSchema", &paths)
+		for _, p := range paths {
+			payloadStr, _ = util.RenameKey(payloadStr, p, p[:len(p)-len("parametersJsonSchema")]+"parameters")
+		}
 
-	if useAntigravitySchema {
-		payloadStr = util.CleanJSONSchemaForAntigravity(payloadStr)
+		if useAntigravitySchema {
+			payloadStr = util.CleanJSONSchemaForAntigravity(payloadStr)
+		} else {
+			payloadStr = util.CleanJSONSchemaForGemini(payloadStr)
+		}
+
+		if strings.Contains(modelName, "claude") {
+			updated, _ := sjson.SetBytes([]byte(payloadStr), "request.toolConfig.functionCallingConfig.mode", "VALIDATED")
+			payloadStr = string(updated)
+		} else {
+			payloadStr, _ = sjson.Delete(payloadStr, "request.generationConfig.maxOutputTokens")
+		}
+
+		bodyReader = strings.NewReader(payloadStr)
+		if e.cfg != nil && e.cfg.RequestLog {
+			payloadLog = []byte(payloadStr)
+		}
 	} else {
-		payloadStr = util.CleanJSONSchemaForGemini(payloadStr)
+		if strings.Contains(modelName, "claude") {
+			payload, _ = sjson.SetBytes(payload, "request.toolConfig.functionCallingConfig.mode", "VALIDATED")
+		} else {
+			payload, _ = sjson.DeleteBytes(payload, "request.generationConfig.maxOutputTokens")
+		}
+
+		bodyReader = bytes.NewReader(payload)
+		if e.cfg != nil && e.cfg.RequestLog {
+			payloadLog = append([]byte(nil), payload...)
+		}
 	}
 
 	// if useAntigravitySchema {
@@ -1972,14 +2001,7 @@ func (e *AntigravityExecutor) buildRequest(ctx context.Context, auth *cliproxyau
 	// 	}
 	// }
 
-	if strings.Contains(modelName, "claude") {
-		updated, _ := sjson.SetBytes([]byte(payloadStr), "request.toolConfig.functionCallingConfig.mode", "VALIDATED")
-		payloadStr = string(updated)
-	} else {
-		payloadStr, _ = sjson.Delete(payloadStr, "request.generationConfig.maxOutputTokens")
-	}
-
-	httpReq, errReq := http.NewRequestWithContext(ctx, http.MethodPost, requestURL.String(), strings.NewReader(payloadStr))
+	httpReq, errReq := http.NewRequestWithContext(ctx, http.MethodPost, requestURL.String(), bodyReader)
 	if errReq != nil {
 		return nil, errReq
 	}
@@ -2002,10 +2024,6 @@ func (e *AntigravityExecutor) buildRequest(ctx context.Context, auth *cliproxyau
 		authLabel = auth.Label
 		authType, authValue = auth.AccountInfo()
 	}
-	var payloadLog []byte
-	if e.cfg != nil && e.cfg.RequestLog {
-		payloadLog = []byte(payloadStr)
-	}
 	helps.RecordAPIRequest(ctx, e.cfg, helps.UpstreamRequestLog{
 		URL:       requestURL.String(),
 		Method:    http.MethodPost,
@@ -2021,6 +2039,19 @@ func (e *AntigravityExecutor) buildRequest(ctx context.Context, auth *cliproxyau
 	return httpReq, nil
 }
 
+func antigravityRequestNeedsSchemaSanitization(payload []byte) bool {
+	if gjson.GetBytes(payload, "request.tools.0").Exists() {
+		return true
+	}
+	if gjson.GetBytes(payload, "request.generationConfig.responseJsonSchema").Exists() {
+		return true
+	}
+	if gjson.GetBytes(payload, "request.generationConfig.responseSchema").Exists() {
+		return true
+	}
+	return false
+}
+
 func tokenExpiry(metadata map[string]any) time.Time {
 	if metadata == nil {
 		return time.Time{}
diff --git a/internal/runtime/executor/antigravity_executor_buildrequest_test.go b/internal/runtime/executor/antigravity_executor_buildrequest_test.go
index 27dbeca49..ed2d79e63 100644
--- a/internal/runtime/executor/antigravity_executor_buildrequest_test.go
+++ b/internal/runtime/executor/antigravity_executor_buildrequest_test.go
@@ -35,12 +35,102 @@ func TestAntigravityBuildRequest_SanitizesAntigravityToolSchema(t *testing.T) {
 	assertSchemaSanitizedAndPropertyPreserved(t, params)
 }
 
-func buildRequestBodyFromPayload(t *testing.T, modelName string) map[string]any {
+func TestAntigravityBuildRequest_SkipsSchemaSanitizationWithoutToolsField(t *testing.T) {
+	body := buildRequestBodyFromRawPayload(t, "gemini-3.1-flash-image", []byte(`{
+		"request": {
+			"contents": [
+				{
+					"role": "user",
+					"x-debug": "keep-me",
+					"parts": [
+						{
+							"text": "hello"
+						}
+					]
+				}
+			],
+			"nonSchema": {
+				"nullable": true,
+				"x-extra": "keep-me"
+			},
+			"generationConfig": {
+				"maxOutputTokens": 128
+			}
+		}
+	}`))
+
+	assertNonSchemaRequestPreserved(t, body)
+}
+
+func TestAntigravityBuildRequest_SkipsSchemaSanitizationWithEmptyToolsArray(t *testing.T) {
+	body := buildRequestBodyFromRawPayload(t, "gemini-3.1-flash-image", []byte(`{
+		"request": {
+			"tools": [],
+			"contents": [
+				{
+					"role": "user",
+					"x-debug": "keep-me",
+					"parts": [
+						{
+							"text": "hello"
+						}
+					]
+				}
+			],
+			"nonSchema": {
+				"nullable": true,
+				"x-extra": "keep-me"
+			},
+			"generationConfig": {
+				"maxOutputTokens": 128
+			}
+		}
+	}`))
+
+	assertNonSchemaRequestPreserved(t, body)
+}
+
+func assertNonSchemaRequestPreserved(t *testing.T, body map[string]any) {
 	t.Helper()
 
-	executor := &AntigravityExecutor{}
-	auth := &cliproxyauth.Auth{}
-	payload := []byte(`{
+	request, ok := body["request"].(map[string]any)
+	if !ok {
+		t.Fatalf("request missing or invalid type")
+	}
+
+	contents, ok := request["contents"].([]any)
+	if !ok || len(contents) == 0 {
+		t.Fatalf("contents missing or empty")
+	}
+	content, ok := contents[0].(map[string]any)
+	if !ok {
+		t.Fatalf("content missing or invalid type")
+	}
+	if got, ok := content["x-debug"].(string); !ok || got != "keep-me" {
+		t.Fatalf("x-debug should be preserved when no tool schema exists, got=%v", content["x-debug"])
+	}
+
+	nonSchema, ok := request["nonSchema"].(map[string]any)
+	if !ok {
+		t.Fatalf("nonSchema missing or invalid type")
+	}
+	if _, ok := nonSchema["nullable"]; !ok {
+		t.Fatalf("nullable should be preserved outside schema cleanup path")
+	}
+	if got, ok := nonSchema["x-extra"].(string); !ok || got != "keep-me" {
+		t.Fatalf("x-extra should be preserved outside schema cleanup path, got=%v", nonSchema["x-extra"])
+	}
+
+	if generationConfig, ok := request["generationConfig"].(map[string]any); ok {
+		if _, ok := generationConfig["maxOutputTokens"]; ok {
+			t.Fatalf("maxOutputTokens should still be removed for non-Claude requests")
+		}
+	}
+}
+
+func buildRequestBodyFromPayload(t *testing.T, modelName string) map[string]any {
+	t.Helper()
+	return buildRequestBodyFromRawPayload(t, modelName, []byte(`{
 		"request": {
 			"tools": [
 				{
@@ -75,7 +165,14 @@ func buildRequestBodyFromPayload(t *testing.T, modelName string) map[string]any
 				}
 			]
 		}
-	}`)
+	}`))
+}
+
+func buildRequestBodyFromRawPayload(t *testing.T, modelName string, payload []byte) map[string]any {
+	t.Helper()
+
+	executor := &AntigravityExecutor{}
+	auth := &cliproxyauth.Auth{}
 
 	req, err := executor.buildRequest(context.Background(), auth, "token", modelName, payload, false, "", "https://example.com")
 	if err != nil {