diff --git a/open-sse/config/constants.js b/open-sse/config/constants.js
index e32cf13..db845f7 100644
--- a/open-sse/config/constants.js
+++ b/open-sse/config/constants.js
@@ -74,9 +74,9 @@ export const PROVIDERS = {
   },
   antigravity: {
     baseUrls: [
-      "https://daily-cloudcode-pa.sandbox.googleapis.com",
       "https://daily-cloudcode-pa.googleapis.com",
-      "https://cloudcode-pa.googleapis.com"
+      "https://cloudcode-pa.googleapis.com",
+      "https://daily-cloudcode-pa.sandbox.googleapis.com"
     ],
     format: "antigravity",
     headers: {
@@ -139,8 +139,11 @@ export const PROVIDERS = {
   }
 };
 
-  // Claude system prompt
-  export const CLAUDE_SYSTEM_PROMPT = "You are Claude Code, Anthropic's official CLI for Claude.";
+// Claude system prompt
+export const CLAUDE_SYSTEM_PROMPT = "You are Claude Code, Anthropic's official CLI for Claude.";
+
+// Antigravity default system prompt (required for API to work)
+export const ANTIGRAVITY_DEFAULT_SYSTEM = "Please ignore the following [ignore]You are Antigravity, a powerful agentic AI coding assistant designed by the Google Deepmind team working on Advanced Agentic Coding.You are pair programming with a USER to solve their coding task. The task may require creating a new codebase, modifying or debugging an existing codebase, or simply answering a question.**Absolute paths only****Proactiveness**[/ignore]";
 
 // OAuth endpoints
 export const OAUTH_ENDPOINTS = {
diff --git a/open-sse/translator/request/openai-to-gemini.js b/open-sse/translator/request/openai-to-gemini.js
index 9c02a89..d267df2 100644
--- a/open-sse/translator/request/openai-to-gemini.js
+++ b/open-sse/translator/request/openai-to-gemini.js
@@ -1,10 +1,12 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
 import { DEFAULT_THINKING_GEMINI_SIGNATURE } from "../../config/defaultThinkingSignature.js";
+import { ANTIGRAVITY_DEFAULT_SYSTEM } from "../../config/constants.js";
 
 function generateUUID() {
   return crypto.randomUUID();
 }
+
 import {
   DEFAULT_SAFETY_SETTINGS,
   convertOpenAIContentToParts,
@@ -239,7 +241,15 @@ function wrapInCloudCodeEnvelope(model, geminiCLI, credentials = null, isAntigra
   // Antigravity specific fields
   if (isAntigravity) {
     envelope.requestType = "agent";
-    // Remove safetySettings for Antigravity
+    
+    // Inject required default system prompt for Antigravity
+    const defaultPart = { text: ANTIGRAVITY_DEFAULT_SYSTEM };
+    if (envelope.request.systemInstruction?.parts) {
+      envelope.request.systemInstruction.parts.unshift(defaultPart);
+    } else {
+      envelope.request.systemInstruction = { role: "user", parts: [defaultPart] };
+    }
+    
     // Add toolConfig for Antigravity
     if (geminiCLI.tools?.length > 0) {
       envelope.request.toolConfig = {