diff --git a/internal/runtime/executor/antigravity_executor.go b/internal/runtime/executor/antigravity_executor.go
index 074dc9fad..163b2d927 100644
--- a/internal/runtime/executor/antigravity_executor.go
+++ b/internal/runtime/executor/antigravity_executor.go
@@ -26,6 +26,7 @@ import (
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/cache"
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/misc"
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/registry"
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/runtime/executor/helps"
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/thinking"
 	antigravityclaude "github.com/router-for-me/CLIProxyAPI/v6/internal/translator/antigravity/claude"
@@ -1955,6 +1956,15 @@ func (e *AntigravityExecutor) buildRequest(ctx context.Context, auth *cliproxyau
 	payload = geminiToAntigravity(modelName, payload, projectID)
 	payload, _ = sjson.SetBytes(payload, "model", modelName)
 
+	// Cap maxOutputTokens to model's max_completion_tokens from registry
+	if maxOut := gjson.GetBytes(payload, "request.generationConfig.maxOutputTokens"); maxOut.Exists() && maxOut.Type == gjson.Number {
+		if modelInfo := registry.LookupModelInfo(modelName, "antigravity"); modelInfo != nil && modelInfo.MaxCompletionTokens > 0 {
+			if int(maxOut.Int()) > modelInfo.MaxCompletionTokens {
+				payload, _ = sjson.SetBytes(payload, "request.generationConfig.maxOutputTokens", modelInfo.MaxCompletionTokens)
+			}
+		}
+	}
+
 	useAntigravitySchema := strings.Contains(modelName, "claude") || strings.Contains(modelName, "gemini-3-pro") || strings.Contains(modelName, "gemini-3.1-pro")
 	var (
 		bodyReader io.Reader