diff --git a/open-sse/config/constants.js b/open-sse/config/constants.js
index ee456100..709c932b 100644
--- a/open-sse/config/constants.js
+++ b/open-sse/config/constants.js
@@ -1,3 +1,76 @@
+import { platform, arch } from "os";
+
+// === Antigravity Binary Alignment: Numeric Enums ===
+// Reference: Antigravity binary analysis - google.internal.cloud.code.v1internal.ClientMetadata
+
+// IDE Type enum (numeric values as expected by Cloud Code API)
+export const IDE_TYPE = {
+  UNSPECIFIED: 0,
+  JETSKI: 10,        // Internal codename for Gemini CLI
+  ANTIGRAVITY: 9,
+  PLUGINS: 7
+};
+
+// Platform enum (as specified in Antigravity binary)
+export const PLATFORM = {
+  UNSPECIFIED: 0,
+  DARWIN_AMD64: 1,
+  DARWIN_ARM64: 2,
+  LINUX_AMD64: 3,
+  LINUX_ARM64: 4,
+  WINDOWS_AMD64: 5
+};
+
+// Plugin type enum (as specified in Antigravity binary)
+export const PLUGIN_TYPE = {
+  UNSPECIFIED: 0,
+  CLOUD_CODE: 1,
+  GEMINI: 2
+};
+
+/**
+ * Get the platform enum value based on the current OS.
+ * @returns {number} Platform enum value
+ */
+export function getPlatformEnum() {
+  const os = platform();
+  const architecture = arch();
+
+  if (os === "darwin") {
+    return architecture === "arm64" ? PLATFORM.DARWIN_ARM64 : PLATFORM.DARWIN_AMD64;
+  } else if (os === "linux") {
+    return architecture === "arm64" ? PLATFORM.LINUX_ARM64 : PLATFORM.LINUX_AMD64;
+  } else if (os === "win32") {
+    return PLATFORM.WINDOWS_AMD64;
+  }
+  return PLATFORM.UNSPECIFIED;
+}
+
+/**
+ * Generate platform-specific User-Agent string.
+ * @returns {string} User-Agent in format "antigravity/version os/arch"
+ */
+export function getPlatformUserAgent() {
+  const os = platform();
+  const architecture = arch();
+  return `antigravity/1.16.5 ${os}/${architecture}`;
+}
+
+// Centralized client metadata (used in request bodies for loadCodeAssist, onboardUser, etc.)
+// Using numeric enum values as expected by the Cloud Code API
+export const CLIENT_METADATA = {
+  ideType: IDE_TYPE.ANTIGRAVITY,   // 9 - identifies as Antigravity client
+  platform: getPlatformEnum(),      // Runtime platform detection
+  pluginType: PLUGIN_TYPE.GEMINI    // 2
+};
+
+// Antigravity headers
+export const ANTIGRAVITY_HEADERS = {
+  "X-Client-Name": "antigravity",
+  "X-Client-Version": "1.107.0",
+  "x-goog-api-client": "gl-node/18.18.2 fire/0.8.6 grpc/1.10.x"
+};
+
 // Provider configurations
 export const PROVIDERS = {
   claude: {
@@ -78,7 +151,7 @@ export const PROVIDERS = {
     ],
     format: "antigravity",
     headers: {
-      "User-Agent": "antigravity/1.104.0 darwin/arm64"
+      "User-Agent": getPlatformUserAgent()
     },
     clientId: "1071006060591-tmhssin2h21lcre235vtolojh4g403ep.apps.googleusercontent.com",
     clientSecret: "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"
@@ -181,7 +254,7 @@ export const PROVIDERS = {
 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]";
+export const ANTIGRAVITY_DEFAULT_SYSTEM = "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**";
 
 // OAuth endpoints
 export const OAUTH_ENDPOINTS = {
diff --git a/open-sse/executors/antigravity.js b/open-sse/executors/antigravity.js
index 1e0c1fad..eb19320b 100644
--- a/open-sse/executors/antigravity.js
+++ b/open-sse/executors/antigravity.js
@@ -1,6 +1,7 @@
 import crypto from "crypto";
 import { BaseExecutor } from "./base.js";
-import { PROVIDERS, OAUTH_ENDPOINTS, HTTP_STATUS } from "../config/constants.js";
+import { PROVIDERS, OAUTH_ENDPOINTS, HTTP_STATUS, ANTIGRAVITY_HEADERS } from "../config/constants.js";
+import { deriveSessionId, getCachedSignature } from "../utils/sessionManager.js";
 
 const MAX_RETRY_AFTER_MS = 10000;
 
@@ -16,19 +17,31 @@ export class AntigravityExecutor extends BaseExecutor {
     return `${baseUrl}/v1internal:${action}`;
   }
 
-  buildHeaders(credentials, stream = true) {
+  buildHeaders(credentials, stream = true, sessionId = null) {
     return {
       "Content-Type": "application/json",
       "Authorization": `Bearer ${credentials.accessToken}`,
       "User-Agent": this.config.headers?.["User-Agent"] || "antigravity/1.104.0 darwin/arm64",
-      "X-9Router-Source": "9router",
+      ...ANTIGRAVITY_HEADERS,
+      ...(sessionId && { "X-Machine-Session-Id": sessionId }),
       ...(stream && { "Accept": "text/event-stream" })
     };
   }
 
   transformRequest(model, body, stream, credentials) {
     const projectId = credentials?.projectId || this.generateProjectId();
-    
+
+    const sessionId = body.request?.sessionId || deriveSessionId(credentials?.email || credentials?.connectionId);
+
+    // Get signature for this session (side-channel cache)
+    const cachedSignature = getCachedSignature(sessionId);
+    // DEBUG LOG
+    if (cachedSignature) {
+      console.log(`[AntigravityExecutor] Injecting cached signature for session ${sessionId.substring(0, 8)}...`);
+    } else {
+      // console.log(`[AntigravityExecutor] No cached signature for session ${sessionId.substring(0, 8)}...`);
+    }
+
     // Fix contents for Claude models via Antigravity
     const contents = body.request?.contents?.map(c => {
       let role = c.role;
@@ -36,8 +49,19 @@ export class AntigravityExecutor extends BaseExecutor {
       if (c.parts?.some(p => p.functionResponse)) {
         role = "user";
       }
-      // Strip thought-only parts, keep thoughtSignature on functionCall parts (Gemini 3+ requires it)
-      const parts = c.parts?.filter(p => {
+
+      // Inject signature into functionCall parts
+      let parts = c.parts?.map(p => {
+        if (p.functionCall) {
+          // Use cached signature or random fallback to avoid static fingerprint
+          const signature = cachedSignature || crypto.randomUUID();
+          return { ...p, thoughtSignature: signature };
+        }
+        return p;
+      });
+
+      // Strip thought-only parts
+      parts = parts?.filter(p => {
         if (p.thought && !p.functionCall) return false;
         if (p.thoughtSignature && !p.functionCall && !p.text) return false;
         return true;
@@ -51,13 +75,13 @@ export class AntigravityExecutor extends BaseExecutor {
     const transformedRequest = {
       ...body.request,
       ...(contents && { contents }),
-      sessionId: body.request?.sessionId || this.generateSessionId(),
+      sessionId: sessionId,
       safetySettings: undefined,
-      toolConfig: body.request?.tools?.length > 0 
+      toolConfig: body.request?.tools?.length > 0
         ? { functionCallingConfig: { mode: "VALIDATED" } }
         : body.request?.toolConfig
     };
-    
+
     return {
       ...body,
       project: projectId,
@@ -108,7 +132,7 @@ export class AntigravityExecutor extends BaseExecutor {
   }
 
   generateSessionId() {
-    return `-${Math.floor(Math.random() * 9_000_000_000_000_000_000)}`;
+    return crypto.randomUUID() + Date.now().toString();
   }
 
   parseRetryHeaders(headers) {
@@ -118,7 +142,7 @@ export class AntigravityExecutor extends BaseExecutor {
     if (retryAfter) {
       const seconds = parseInt(retryAfter, 10);
       if (!isNaN(seconds) && seconds > 0) return seconds * 1000;
-      
+
       const date = new Date(retryAfter);
       if (!isNaN(date.getTime())) {
         const diff = date.getTime() - Date.now();
@@ -167,9 +191,10 @@ export class AntigravityExecutor extends BaseExecutor {
 
     for (let urlIndex = 0; urlIndex < fallbackCount; urlIndex++) {
       const url = this.buildUrl(model, stream, urlIndex);
-      const headers = this.buildHeaders(credentials, stream);
       const transformedBody = this.transformRequest(model, body, stream, credentials);
-      
+      const sessionId = transformedBody.request?.sessionId;
+      const headers = this.buildHeaders(credentials, stream, sessionId);
+
       // Initialize retry counter for this URL
       if (!retryAttemptsByUrl[urlIndex]) {
         retryAttemptsByUrl[urlIndex] = 0;
@@ -200,7 +225,7 @@ export class AntigravityExecutor extends BaseExecutor {
           }
 
           if (retryMs && retryMs <= MAX_RETRY_AFTER_MS) {
-            log?.debug?.("RETRY", `${response.status} with Retry-After: ${Math.ceil(retryMs/1000)}s, waiting...`);
+            log?.debug?.("RETRY", `${response.status} with Retry-After: ${Math.ceil(retryMs / 1000)}s, waiting...`);
             await new Promise(resolve => setTimeout(resolve, retryMs));
             urlIndex--;
             continue;
@@ -211,15 +236,15 @@ export class AntigravityExecutor extends BaseExecutor {
             retryAttemptsByUrl[urlIndex]++;
             // Exponential backoff: 2s, 4s, 8s...
             const backoffMs = Math.min(1000 * (2 ** retryAttemptsByUrl[urlIndex]), MAX_RETRY_AFTER_MS);
-            log?.debug?.("RETRY", `429 auto retry ${retryAttemptsByUrl[urlIndex]}/${MAX_AUTO_RETRIES} after ${backoffMs/1000}s`);
+            log?.debug?.("RETRY", `429 auto retry ${retryAttemptsByUrl[urlIndex]}/${MAX_AUTO_RETRIES} after ${backoffMs / 1000}s`);
             await new Promise(resolve => setTimeout(resolve, backoffMs));
             urlIndex--;
             continue;
           }
 
-          log?.debug?.("RETRY", `${response.status}, Retry-After ${retryMs ? `too long (${Math.ceil(retryMs/1000)}s)` : 'missing'}, trying fallback`);
+          log?.debug?.("RETRY", `${response.status}, Retry-After ${retryMs ? `too long (${Math.ceil(retryMs / 1000)}s)` : 'missing'}, trying fallback`);
           lastStatus = response.status;
-          
+
           if (urlIndex + 1 < fallbackCount) {
             continue;
           }
diff --git a/open-sse/services/usage.js b/open-sse/services/usage.js
index 673cae20..8a34038f 100644
--- a/open-sse/services/usage.js
+++ b/open-sse/services/usage.js
@@ -2,6 +2,8 @@
  * Usage Fetcher - Get usage data from provider APIs
  */
 
+import { CLIENT_METADATA, getPlatformUserAgent } from "../config/constants.js";
+
 // GitHub API config
 const GITHUB_CONFIG = {
   apiVersion: "2022-11-28",
@@ -15,7 +17,7 @@ const ANTIGRAVITY_CONFIG = {
   tokenUrl: "https://oauth2.googleapis.com/token",
   clientId: "1071006060591-tmhssin2h21lcre235vtolojh4g403ep.apps.googleusercontent.com",
   clientSecret: "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",
-  userAgent: "antigravity/1.11.3 Darwin/arm64",
+  userAgent: getPlatformUserAgent(),
 };
 
 // Codex (OpenAI) API config
@@ -65,23 +67,23 @@ export async function getUsageForProvider(connection) {
  */
 function parseResetTime(resetValue) {
   if (!resetValue) return null;
-  
+
   try {
     // If it's already a Date object
     if (resetValue instanceof Date) {
       return resetValue.toISOString();
     }
-    
+
     // If it's a number (Unix timestamp in milliseconds)
     if (typeof resetValue === 'number') {
       return new Date(resetValue).toISOString();
     }
-    
+
     // If it's a string (ISO date or any parseable date string)
     if (typeof resetValue === 'string') {
       return new Date(resetValue).toISOString();
     }
-    
+
     return null;
   } catch (error) {
     console.warn(`Failed to parse reset time: ${resetValue}`, error);
@@ -98,7 +100,7 @@ async function getGitHubUsage(accessToken, providerSpecificData) {
     if (!accessToken) {
       throw new Error("No GitHub access token available. Please re-authorize the connection.");
     }
-    
+
     // copilot_internal/user API requires GitHub OAuth token, not copilotToken
     const response = await fetch("https://api.github.com/copilot_internal/user", {
       headers: {
@@ -123,7 +125,7 @@ async function getGitHubUsage(accessToken, providerSpecificData) {
       // Paid plan format
       const snapshots = data.quota_snapshots;
       const resetAt = parseResetTime(data.quota_reset_date);
-      
+
       return {
         plan: data.copilot_plan,
         resetDate: data.quota_reset_date,
@@ -138,7 +140,7 @@ async function getGitHubUsage(accessToken, providerSpecificData) {
       const monthlyQuotas = data.monthly_quotas || {};
       const usedQuotas = data.limited_user_quotas || {};
       const resetAt = parseResetTime(data.limited_user_reset_date);
-      
+
       return {
         plan: data.copilot_plan || data.access_type_sku,
         resetDate: data.limited_user_reset_date,
@@ -167,7 +169,7 @@ async function getGitHubUsage(accessToken, providerSpecificData) {
 
 function formatGitHubQuotaSnapshot(quota) {
   if (!quota) return { used: 0, total: 0, unlimited: true };
-  
+
   return {
     used: quota.entitlement - quota.remaining,
     total: quota.entitlement,
@@ -211,7 +213,7 @@ async function getAntigravityUsage(accessToken, providerSpecificData) {
   try {
     // First get project ID from subscription info
     const projectId = await getAntigravityProjectId(accessToken);
-    
+
     // Fetch quota data
     const response = await fetch(ANTIGRAVITY_CONFIG.quotaApiUrl, {
       method: "POST",
@@ -220,7 +222,11 @@ async function getAntigravityUsage(accessToken, providerSpecificData) {
         "User-Agent": ANTIGRAVITY_CONFIG.userAgent,
         "Content-Type": "application/json",
       },
-      body: JSON.stringify(projectId ? { project: projectId } : {}),
+      body: JSON.stringify({
+        ...(projectId ? { project: projectId } : {}),
+        metadata: CLIENT_METADATA,
+        mode: 1
+      }),
     });
 
     if (response.status === 403) {
@@ -233,7 +239,7 @@ async function getAntigravityUsage(accessToken, providerSpecificData) {
 
     const data = await response.json();
     const quotas = {};
-    
+
     // Parse model quotas (inspired by vscode-antigravity-cockpit)
     if (data.models) {
       // Filter only recommended/important models (must match PROVIDER_MODELS ag ids)
@@ -248,26 +254,26 @@ async function getAntigravityUsage(accessToken, providerSpecificData) {
         'gemini-3-flash',
         'gemini-2.5-flash',
       ];
-      
+
       for (const [modelKey, info] of Object.entries(data.models)) {
         // Skip models without quota info
         if (!info.quotaInfo) {
           continue;
         }
-        
+
         // Skip internal models and non-important models
         if (info.isInternal || !importantModels.includes(modelKey)) {
           continue;
         }
-        
+
         const remainingFraction = info.quotaInfo.remainingFraction || 0;
         const remainingPercentage = remainingFraction * 100;
-        
+
         // Convert percentage to used/total for UI compatibility
         const total = 1000; // Normalized base
         const remaining = Math.round(total * remainingFraction);
         const used = total - remaining;
-        
+
         // Use modelKey as key (matches PROVIDER_MODELS id)
         quotas[modelKey] = {
           used,
@@ -317,7 +323,7 @@ async function getAntigravitySubscriptionInfo(accessToken) {
         "User-Agent": ANTIGRAVITY_CONFIG.userAgent,
         "Content-Type": "application/json",
       },
-      body: JSON.stringify({ metadata: { ideType: "ANTIGRAVITY" } }),
+      body: JSON.stringify({ metadata: CLIENT_METADATA, mode: 1 }),
     });
 
     if (!response.ok) return null;
@@ -345,7 +351,7 @@ async function getClaudeUsage(accessToken) {
 
     if (settingsResponse.ok) {
       const settings = await settingsResponse.json();
-      
+
       // Try usage endpoint if we have org info
       if (settings.organization_id) {
         const usageResponse = await fetch(
@@ -402,7 +408,7 @@ async function getCodexUsage(accessToken) {
     }
 
     const data = await response.json();
-    
+
     // Parse rate limit info
     const rateLimit = data.rate_limit || {};
     const primaryWindow = rateLimit.primary_window || {};
@@ -475,7 +481,7 @@ async function getKiroUsage(accessToken, providerSpecificData) {
     // Parse usage data from usageBreakdownList
     const usageList = data.usageBreakdownList || [];
     const quotaInfo = {};
-    
+
     // Parse reset time - supports multiple formats (nextDateReset, resetDate, etc.)
     const resetAt = parseResetTime(data.nextDateReset || data.resetDate);
 
@@ -483,7 +489,7 @@ async function getKiroUsage(accessToken, providerSpecificData) {
       const resourceType = breakdown.resourceType?.toLowerCase() || "unknown";
       const used = breakdown.currentUsageWithPrecision || 0;
       const total = breakdown.usageLimitWithPrecision || 0;
-      
+
       quotaInfo[resourceType] = {
         used,
         total,
@@ -496,7 +502,7 @@ async function getKiroUsage(accessToken, providerSpecificData) {
       if (breakdown.freeTrialInfo) {
         const freeUsed = breakdown.freeTrialInfo.currentUsageWithPrecision || 0;
         const freeTotal = breakdown.freeTrialInfo.usageLimitWithPrecision || 0;
-        
+
         quotaInfo[`${resourceType}_freetrial`] = {
           used: freeUsed,
           total: freeTotal,
diff --git a/open-sse/translator/helpers/geminiHelper.js b/open-sse/translator/helpers/geminiHelper.js
index 01368993..8b5ef582 100644
--- a/open-sse/translator/helpers/geminiHelper.js
+++ b/open-sse/translator/helpers/geminiHelper.js
@@ -35,7 +35,7 @@ export const DEFAULT_SAFETY_SETTINGS = [
 // Convert OpenAI content to Gemini parts
 export function convertOpenAIContentToParts(content) {
   const parts = [];
-  
+
   if (typeof content === "string") {
     parts.push({ text: content });
   } else if (Array.isArray(content)) {
@@ -57,7 +57,7 @@ export function convertOpenAIContentToParts(content) {
       }
     }
   }
-  
+
   return parts;
 }
 
@@ -85,9 +85,9 @@ export function generateRequestId() {
   return `agent-${crypto.randomUUID()}`;
 }
 
-// Generate session ID
+// Generate session ID (binary-compatible format: UUID + timestamp)
 export function generateSessionId() {
-  return `-${Math.floor(Math.random() * 9000000000000000000)}`;
+  return crypto.randomUUID() + Date.now().toString();
 }
 
 // Generate project ID
@@ -102,7 +102,7 @@ export function generateProjectId() {
 // Helper: Remove unsupported keywords recursively from object/array
 function removeUnsupportedKeywords(obj, keywords) {
   if (!obj || typeof obj !== "object") return;
-  
+
   if (Array.isArray(obj)) {
     for (const item of obj) {
       removeUnsupportedKeywords(item, keywords);
@@ -126,12 +126,12 @@ function removeUnsupportedKeywords(obj, keywords) {
 // Convert const to enum
 function convertConstToEnum(obj) {
   if (!obj || typeof obj !== "object") return;
-  
+
   if (obj.const !== undefined && !obj.enum) {
     obj.enum = [obj.const];
     delete obj.const;
   }
-  
+
   for (const value of Object.values(obj)) {
     if (value && typeof value === "object") {
       convertConstToEnum(value);
@@ -142,11 +142,11 @@ function convertConstToEnum(obj) {
 // Convert enum values to strings (Gemini requires string enum values)
 function convertEnumValuesToStrings(obj) {
   if (!obj || typeof obj !== "object") return;
-  
+
   if (obj.enum && Array.isArray(obj.enum)) {
     obj.enum = obj.enum.map(v => String(v));
   }
-  
+
   for (const value of Object.values(obj)) {
     if (value && typeof value === "object") {
       convertEnumValuesToStrings(value);
@@ -157,10 +157,10 @@ function convertEnumValuesToStrings(obj) {
 // Merge allOf schemas
 function mergeAllOf(obj) {
   if (!obj || typeof obj !== "object") return;
-  
+
   if (obj.allOf && Array.isArray(obj.allOf)) {
     const merged = {};
-    
+
     for (const item of obj.allOf) {
       if (item.properties) {
         if (!merged.properties) merged.properties = {};
@@ -175,12 +175,12 @@ function mergeAllOf(obj) {
         }
       }
     }
-    
+
     delete obj.allOf;
     if (merged.properties) obj.properties = { ...obj.properties, ...merged.properties };
     if (merged.required) obj.required = [...(obj.required || []), ...merged.required];
   }
-  
+
   for (const value of Object.values(obj)) {
     if (value && typeof value === "object") {
       mergeAllOf(value);
@@ -192,12 +192,12 @@ function mergeAllOf(obj) {
 function selectBest(items) {
   let bestIdx = 0;
   let bestScore = -1;
-  
+
   for (let i = 0; i < items.length; i++) {
     const item = items[i];
     let score = 0;
     const type = item.type;
-    
+
     if (type === "object" || item.properties) {
       score = 3;
     } else if (type === "array" || item.items) {
@@ -205,20 +205,20 @@ function selectBest(items) {
     } else if (type && type !== "null") {
       score = 1;
     }
-    
+
     if (score > bestScore) {
       bestScore = score;
       bestIdx = i;
     }
   }
-  
+
   return bestIdx;
 }
 
 // Flatten anyOf/oneOf
 function flattenAnyOfOneOf(obj) {
   if (!obj || typeof obj !== "object") return;
-  
+
   if (obj.anyOf && Array.isArray(obj.anyOf) && obj.anyOf.length > 0) {
     const nonNullSchemas = obj.anyOf.filter(s => s && s.type !== "null");
     if (nonNullSchemas.length > 0) {
@@ -228,7 +228,7 @@ function flattenAnyOfOneOf(obj) {
       Object.assign(obj, selected);
     }
   }
-  
+
   if (obj.oneOf && Array.isArray(obj.oneOf) && obj.oneOf.length > 0) {
     const nonNullSchemas = obj.oneOf.filter(s => s && s.type !== "null");
     if (nonNullSchemas.length > 0) {
@@ -238,7 +238,7 @@ function flattenAnyOfOneOf(obj) {
       Object.assign(obj, selected);
     }
   }
-  
+
   for (const value of Object.values(obj)) {
     if (value && typeof value === "object") {
       flattenAnyOfOneOf(value);
@@ -249,12 +249,12 @@ function flattenAnyOfOneOf(obj) {
 // Flatten type arrays
 function flattenTypeArrays(obj) {
   if (!obj || typeof obj !== "object") return;
-  
+
   if (obj.type && Array.isArray(obj.type)) {
     const nonNullTypes = obj.type.filter(t => t !== "null");
     obj.type = nonNullTypes.length > 0 ? nonNullTypes[0] : "string";
   }
-  
+
   for (const value of Object.values(obj)) {
     if (value && typeof value === "object") {
       flattenTypeArrays(value);
@@ -266,28 +266,28 @@ function flattenTypeArrays(obj) {
 // Reference: CLIProxyAPI/internal/util/gemini_schema.go
 export function cleanJSONSchemaForAntigravity(schema) {
   if (!schema || typeof schema !== "object") return schema;
-  
+
   // Mutate directly (schema is only used once per request)
   let cleaned = schema;
-  
+
   // Phase 1: Convert and prepare
   convertConstToEnum(cleaned);
   convertEnumValuesToStrings(cleaned);
-  
+
   // Phase 2: Flatten complex structures
   mergeAllOf(cleaned);
   flattenAnyOfOneOf(cleaned);
   flattenTypeArrays(cleaned);
-  
+
   // Phase 3: Remove all unsupported keywords at ALL levels (including inside arrays)
   removeUnsupportedKeywords(cleaned, UNSUPPORTED_SCHEMA_CONSTRAINTS);
-  
+
   // Phase 4: Cleanup required fields recursively
   function cleanupRequired(obj) {
     if (!obj || typeof obj !== "object") return;
-    
+
     if (obj.required && Array.isArray(obj.required) && obj.properties) {
-      const validRequired = obj.required.filter(field => 
+      const validRequired = obj.required.filter(field =>
         Object.prototype.hasOwnProperty.call(obj.properties, field)
       );
       if (validRequired.length === 0) {
@@ -296,7 +296,7 @@ export function cleanJSONSchemaForAntigravity(schema) {
         obj.required = validRequired;
       }
     }
-    
+
     // Recurse into nested objects
     for (const value of Object.values(obj)) {
       if (value && typeof value === "object") {
@@ -304,13 +304,13 @@ export function cleanJSONSchemaForAntigravity(schema) {
       }
     }
   }
-  
+
   cleanupRequired(cleaned);
-  
+
   // Phase 5: Add placeholder for empty object schemas (Antigravity requirement)
   function addPlaceholders(obj) {
     if (!obj || typeof obj !== "object") return;
-    
+
     if (obj.type === "object") {
       if (!obj.properties || Object.keys(obj.properties).length === 0) {
         obj.properties = {
@@ -322,7 +322,7 @@ export function cleanJSONSchemaForAntigravity(schema) {
         obj.required = ["reason"];
       }
     }
-    
+
     // Recurse into nested objects
     for (const value of Object.values(obj)) {
       if (value && typeof value === "object") {
@@ -330,9 +330,9 @@ export function cleanJSONSchemaForAntigravity(schema) {
       }
     }
   }
-  
+
   addPlaceholders(cleaned);
-  
+
   return cleaned;
 }
 
diff --git a/open-sse/translator/request/openai-to-gemini.js b/open-sse/translator/request/openai-to-gemini.js
index b48f8644..42bfe85c 100644
--- a/open-sse/translator/request/openai-to-gemini.js
+++ b/open-sse/translator/request/openai-to-gemini.js
@@ -1,6 +1,6 @@
 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";
 import { openaiToClaudeRequestForAntigravity } from "./openai-to-claude.js";
 
@@ -18,6 +18,7 @@ import {
   generateProjectId,
   cleanJSONSchemaForAntigravity
 } from "../helpers/geminiHelper.js";
+import { deriveSessionId } from "../../utils/sessionManager.js";
 
 // Core: Convert OpenAI request to Gemini format (base for all variants)
 function openaiToGeminiBase(model, body, stream) {
@@ -86,17 +87,10 @@ function openaiToGeminiBase(model, body, stream) {
       } else if (role === "assistant") {
         const parts = [];
 
-        // Thinking/reasoning → thought part with signature
-        if (msg.reasoning_content) {
-          parts.push({
-            thought: true,
-            text: msg.reasoning_content
-          });
-          parts.push({
-            thoughtSignature: DEFAULT_THINKING_GEMINI_SIGNATURE,
-            text: ""
-          });
-        }
+        parts.push({
+          thought: true,
+          text: msg.reasoning_content
+        });
 
         if (content) {
           const text = typeof content === "string" ? content : extractTextContent(content);
@@ -112,7 +106,6 @@ function openaiToGeminiBase(model, body, stream) {
 
             const args = tryParseJSON(tc.function?.arguments || "{}");
             parts.push({
-              thoughtSignature: DEFAULT_THINKING_GEMINI_SIGNATURE,
               functionCall: {
                 id: tc.id,
                 name: tc.function.name,
@@ -259,7 +252,7 @@ function wrapInCloudCodeEnvelope(model, geminiCLI, credentials = null, isAntigra
     userAgent: isAntigravity ? "antigravity" : "gemini-cli",
     requestId: isAntigravity ? `agent-${generateUUID()}` : generateRequestId(),
     request: {
-      sessionId: generateSessionId(),
+      sessionId: isAntigravity ? deriveSessionId(credentials?.email || credentials?.connectionId) : generateSessionId(),
       contents: geminiCLI.contents,
       systemInstruction: geminiCLI.systemInstruction,
       generationConfig: geminiCLI.generationConfig,
@@ -272,11 +265,16 @@ function wrapInCloudCodeEnvelope(model, geminiCLI, credentials = null, isAntigra
     envelope.requestType = "agent";
 
     // Inject required default system prompt for Antigravity
-    const defaultPart = { text: ANTIGRAVITY_DEFAULT_SYSTEM };
+    // Inject required default system prompt for Antigravity (double injection)
+    const systemParts = [
+      { text: ANTIGRAVITY_DEFAULT_SYSTEM },
+      { text: `Please ignore the following [ignore]${ANTIGRAVITY_DEFAULT_SYSTEM}[/ignore]` }
+    ];
+
     if (envelope.request.systemInstruction?.parts) {
-      envelope.request.systemInstruction.parts.unshift(defaultPart);
+      envelope.request.systemInstruction.parts.unshift(...systemParts);
     } else {
-      envelope.request.systemInstruction = { role: "user", parts: [defaultPart] };
+      envelope.request.systemInstruction = { role: "user", parts: systemParts };
     }
 
     // Add toolConfig for Antigravity
@@ -304,7 +302,7 @@ function wrapInCloudCodeEnvelopeForClaude(model, claudeRequest, credentials = nu
     requestId: `agent-${generateUUID()}`,
     requestType: "agent",
     request: {
-      sessionId: generateSessionId(),
+      sessionId: deriveSessionId(credentials?.email || credentials?.connectionId),
       contents: [],
       generationConfig: {
         temperature: claudeRequest.temperature || 1,
@@ -378,9 +376,11 @@ function wrapInCloudCodeEnvelopeForClaude(model, claudeRequest, credentials = nu
     }
   }
 
-  // Add system instruction (Antigravity default)
-  const defaultPart = { text: ANTIGRAVITY_DEFAULT_SYSTEM };
-  const systemParts = [defaultPart];
+  // Add system instruction (Antigravity default - double injection)
+  const systemParts = [
+    { text: ANTIGRAVITY_DEFAULT_SYSTEM },
+    { text: `Please ignore the following [ignore]${ANTIGRAVITY_DEFAULT_SYSTEM}[/ignore]` }
+  ];
 
   if (claudeRequest.system) {
     if (Array.isArray(claudeRequest.system)) {
diff --git a/open-sse/translator/response/gemini-to-openai.js b/open-sse/translator/response/gemini-to-openai.js
index 000cc1f7..3cc55b08 100644
--- a/open-sse/translator/response/gemini-to-openai.js
+++ b/open-sse/translator/response/gemini-to-openai.js
@@ -1,5 +1,6 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
+import { cacheSignature } from "../../utils/sessionManager.js";
 
 // Convert Gemini response chunk to OpenAI format
 export function geminiToOpenAIResponse(chunk, state) {
@@ -39,6 +40,13 @@ export function geminiToOpenAIResponse(chunk, state) {
       
       // Handle thought signature (thinking mode)
       if (hasThoughtSig) {
+        // Cache signature if session ID is available
+        const signature = part.thoughtSignature || part.thought_signature;
+        if (state.sessionId && signature) {
+          // DEBUG LOG
+          console.log(`[GeminiToOpenAI] Found signature for session ${state.sessionId.substring(0, 8)}...`);
+          cacheSignature(state.sessionId, signature);
+        }
         const hasTextContent = part.text !== undefined && part.text !== "";
         const hasFunctionCall = !!part.functionCall;
         
diff --git a/open-sse/utils/sessionManager.js b/open-sse/utils/sessionManager.js
new file mode 100644
index 00000000..d447fbb4
--- /dev/null
+++ b/open-sse/utils/sessionManager.js
@@ -0,0 +1,89 @@
+/**
+ * Session Manager for Antigravity Cloud Code
+ *
+ * Handles session ID generation and caching for prompt caching continuity.
+ * Mimics the Antigravity binary behavior: generates a session ID at startup
+ * and keeps it for the process lifetime, scoped per account/connection.
+ *
+ * Reference: antigravity-claude-proxy/src/cloudcode/session-manager.js
+ */
+
+import crypto from "crypto";
+
+// Runtime storage for session IDs (per connection/account)
+// Key: connectionId (email or identifier), Value: sessionId
+const runtimeSessionStore = new Map();
+
+/**
+ * Get or create a session ID for the given connection.
+ *
+ * The binary generates a session ID once at startup: `rs() + Date.now()`.
+ * Since 9router is long-running, we simulate this "per-launch" behavior by
+ * storing a generated ID in memory for each connection.
+ *
+ * - If 9router restarts, the ID changes (matching binary restart behavior).
+ * - Within a running instance, the ID is stable for that connection.
+ * - This enables prompt caching while using the EXACT random logic of the binary.
+// Map to store latest thinking signatures by session ID for side-channel passing
+const runtimeSignatureStore = new Map();
+
+/**
+ * Get or create a session ID for a given connection/account.
+ * Uses the binary-compatible format: UUID + timestamp
+ * uniqueKey should be accountEmail (preferred) or connectionId
+ */
+export function deriveSessionId(uniqueKey) {
+    if (!uniqueKey) {
+        // Fallback if no key provided, but this won't be cached per connection
+        return generateBinaryStyleId();
+    }
+
+    if (runtimeSessionStore.has(uniqueKey)) {
+        return runtimeSessionStore.get(uniqueKey);
+    }
+
+    const newSessionId = generateBinaryStyleId();
+    runtimeSessionStore.set(uniqueKey, newSessionId);
+    return newSessionId;
+}
+
+/**
+ * Cache the latest thinking signature for a session.
+ * This is used to pass signatures from response handling (gemini-to-openai)
+ * to request handling (antigravity executor) side-channel, bypassing
+ * the OpenAI intermediate format which drops them.
+ */
+export function cacheSignature(sessionId, signature) {
+    if (!sessionId || !signature) return;
+    // DEBUG LOG: Caching signature
+    console.log(`[SessionManager] Caching signature for ${sessionId.substring(0, 8)}...: ${signature.substring(0, 20)}...`);
+    runtimeSignatureStore.set(sessionId, signature);
+}
+
+/**
+ * Retrieve the cached thinking signature for a session.
+ */
+export function getCachedSignature(sessionId) {
+    const sig = runtimeSignatureStore.get(sessionId);
+    if (sig) {
+        // DEBUG LOG: Retrieving signature
+        console.log(`[SessionManager] Retrieved signature for ${sessionId.substring(0, 8)}...: ${sig.substring(0, 20)}...`);
+    }
+    return sig;
+}
+
+/**
+ * Generate a session ID in the format expected by Antigravity:
+ * randomUUID + Date.now()
+ */
+export function generateBinaryStyleId() {
+    return crypto.randomUUID() + Date.now().toString();
+}
+
+/**
+ * Clear session store (e.g., on restart or config change)
+ */
+export function clearSessionStore() {
+    runtimeSessionStore.clear();
+    runtimeSignatureStore.clear();
+}
diff --git a/open-sse/utils/stream.js b/open-sse/utils/stream.js
index bcfff891..c042db9a 100644
--- a/open-sse/utils/stream.js
+++ b/open-sse/utils/stream.js
@@ -3,6 +3,7 @@ import { FORMATS } from "../translator/formats.js";
 import { trackPendingRequest, appendRequestLog } from "@/lib/usageDb.js";
 import { extractUsage, hasValidUsage, estimateUsage, logUsage, addBufferToUsage, filterUsageForFormat, COLORS } from "./usageTracking.js";
 import { parseSSELine, hasValuableContent, fixInvalidId, formatSSE } from "./streamHelpers.js";
+import { deriveSessionId } from "./sessionManager.js";
 
 export { COLORS, formatSSE };
 
@@ -49,7 +50,15 @@ export function createSSEStream(options = {}) {
   let buffer = "";
   let usage = null;
 
-  const state = mode === STREAM_MODE.TRANSLATE ? { ...initState(sourceFormat), provider, toolNameMap, model } : null;
+  // Derive session ID for signature caching (if connectionId is available)
+  const sessionId = connectionId ? deriveSessionId(connectionId) : null;
+
+  // DEBUG LOG
+  if (sessionId) {
+    console.log(`[Stream] Associated stream with sessionId: ${sessionId.substring(0, 8)}...`);
+  }
+
+  const state = mode === STREAM_MODE.TRANSLATE ? { ...initState(sourceFormat), provider, toolNameMap, model, sessionId } : null;
 
   let totalContentLength = 0;
   let accumulatedContent = "";
diff --git a/src/lib/oauth/constants/oauth.js b/src/lib/oauth/constants/oauth.js
index d8c59af1..fd1329c4 100644
--- a/src/lib/oauth/constants/oauth.js
+++ b/src/lib/oauth/constants/oauth.js
@@ -1,6 +1,20 @@
 /**
  * OAuth Configuration Constants
  */
+import { platform, arch } from "os";
+
+/**
+ * Get the platform enum value based on the current OS.
+ * Matches Antigravity binary's ClientMetadata.Platform enum.
+ */
+function getOAuthPlatformEnum() {
+  const os = platform();
+  const architecture = arch();
+  if (os === "darwin") return architecture === "arm64" ? 2 : 1;
+  if (os === "linux") return architecture === "arm64" ? 4 : 3;
+  if (os === "win32") return 5;
+  return 0;
+}
 
 // Claude OAuth Configuration (Authorization Code Flow with PKCE)
 export const CLAUDE_CONFIG = {
@@ -83,9 +97,17 @@ export const ANTIGRAVITY_CONFIG = {
   onboardUserEndpoint: "https://cloudcode-pa.googleapis.com/v1internal:onboardUser",
   loadCodeAssistUserAgent: "google-api-nodejs-client/9.15.1",
   loadCodeAssistApiClient: "google-cloud-sdk vscode_cloudshelleditor/0.1",
-  loadCodeAssistClientMetadata: `{"ideType":"IDE_UNSPECIFIED","platform":"PLATFORM_UNSPECIFIED","pluginType":"GEMINI"}`,
+  loadCodeAssistClientMetadata: JSON.stringify({ ideType: 9, platform: getOAuthPlatformEnum(), pluginType: 2 }),
 };
 
+/**
+ * Get client metadata using numeric enum values for API calls.
+ * @returns {{ ideType: number, platform: number, pluginType: number }}
+ */
+export function getOAuthClientMetadata() {
+  return { ideType: 9, platform: getOAuthPlatformEnum(), pluginType: 2 };
+}
+
 // OpenAI OAuth Configuration (Authorization Code Flow with PKCE)
 export const OPENAI_CONFIG = {
   clientId: "app_EMoamEEZ73f0CkXaXp7hrann",
diff --git a/src/lib/oauth/providers.js b/src/lib/oauth/providers.js
index 0ff356b2..8124553d 100644
--- a/src/lib/oauth/providers.js
+++ b/src/lib/oauth/providers.js
@@ -14,6 +14,7 @@ import {
   GITHUB_CONFIG,
   KIRO_CONFIG,
   CURSOR_CONFIG,
+  getOAuthClientMetadata,
 } from "./constants/oauth";
 
 // Provider configurations
@@ -184,7 +185,8 @@ const PROVIDERS = {
               "Content-Type": "application/json",
             },
             body: JSON.stringify({
-              metadata: { ideType: "IDE_UNSPECIFIED", platform: "PLATFORM_UNSPECIFIED", pluginType: "GEMINI" },
+              metadata: getOAuthClientMetadata(),
+              mode: 1,
             }),
           }
         );
@@ -254,7 +256,7 @@ const PROVIDERS = {
         "X-Goog-Api-Client": ANTIGRAVITY_CONFIG.loadCodeAssistApiClient,
         "Client-Metadata": ANTIGRAVITY_CONFIG.loadCodeAssistClientMetadata,
       };
-      const metadata = { ideType: "IDE_UNSPECIFIED", platform: "PLATFORM_UNSPECIFIED", pluginType: "GEMINI" };
+      const metadata = getOAuthClientMetadata();
 
       // Fetch user info
       const userInfoRes = await fetch(`${ANTIGRAVITY_CONFIG.userInfoUrl}?alt=json`, {
@@ -269,7 +271,7 @@ const PROVIDERS = {
         const loadRes = await fetch(ANTIGRAVITY_CONFIG.loadCodeAssistEndpoint, {
           method: "POST",
           headers,
-          body: JSON.stringify({ metadata }),
+          body: JSON.stringify({ metadata, mode: 1 }),
         });
         if (loadRes.ok) {
           const data = await loadRes.json();
@@ -295,7 +297,7 @@ const PROVIDERS = {
             const onboardRes = await fetch(ANTIGRAVITY_CONFIG.onboardUserEndpoint, {
               method: "POST",
               headers,
-              body: JSON.stringify({ tierId, metadata, cloudaicompanionProject: projectId }),
+              body: JSON.stringify({ tierId, metadata, cloudaicompanionProject: projectId, mode: 1 }),
             });
             if (onboardRes.ok) {
               const result = await onboardRes.json();
@@ -727,9 +729,9 @@ export function generateAuthData(providerName, redirectUri) {
  */
 export async function exchangeTokens(providerName, code, redirectUri, codeVerifier, state) {
   const provider = getProvider(providerName);
-  
+
   const tokens = await provider.exchangeToken(provider.config, code, redirectUri, codeVerifier, state);
-  
+
   let extra = null;
   if (provider.postExchange) {
     extra = await provider.postExchange(tokens);
@@ -761,9 +763,9 @@ export async function pollForToken(providerName, deviceCode, codeVerifier, extra
   if (provider.flowType !== "device_code") {
     throw new Error(`Provider ${providerName} does not support device code flow`);
   }
-  
+
   const result = await provider.pollToken(provider.config, deviceCode, codeVerifier, extraData);
-  
+
   if (result.ok) {
     // For device code flows, success is only when we have an access token
     if (result.data.access_token) {
@@ -777,23 +779,23 @@ export async function pollForToken(providerName, deviceCode, codeVerifier, extra
       // Check if it's still pending authorization
       if (result.data.error === 'authorization_pending' || result.data.error === 'slow_down') {
         // This is not a failure, just still waiting
-        return { 
-          success: false, 
-          error: result.data.error, 
+        return {
+          success: false,
+          error: result.data.error,
           errorDescription: result.data.error_description || result.data.message,
           pending: result.data.error === 'authorization_pending'
         };
       } else {
         // Actual error
-        return { 
-          success: false, 
-          error: result.data.error || 'no_access_token', 
-          errorDescription: result.data.error_description || result.data.message || 'No access token received' 
+        return {
+          success: false,
+          error: result.data.error || 'no_access_token',
+          errorDescription: result.data.error_description || result.data.message || 'No access token received'
         };
       }
     }
   }
-  
+
   return { success: false, error: result.data.error, errorDescription: result.data.error_description };
 }
 
diff --git a/src/lib/oauth/services/antigravity.js b/src/lib/oauth/services/antigravity.js
index d9d5eaa6..4d8611ca 100644
--- a/src/lib/oauth/services/antigravity.js
+++ b/src/lib/oauth/services/antigravity.js
@@ -1,4 +1,5 @@
 import crypto from "crypto";
+import { platform, arch } from "os";
 import open from "open";
 import { ANTIGRAVITY_CONFIG } from "../constants/oauth.js";
 import { getServerCredentials } from "../config/index.js";
@@ -92,12 +93,20 @@ export class AntigravityService {
 
   /**
    * Get metadata object for API calls
+   * Uses numeric enum values matching Antigravity binary specifications
    */
   getMetadata() {
+    const os = platform();
+    const architecture = arch();
+    let platformEnum = 0; // UNSPECIFIED
+    if (os === "darwin") platformEnum = architecture === "arm64" ? 2 : 1;
+    else if (os === "linux") platformEnum = architecture === "arm64" ? 4 : 3;
+    else if (os === "win32") platformEnum = 5;
+
     return {
-      ideType: "IDE_UNSPECIFIED",
-      platform: "PLATFORM_UNSPECIFIED",
-      pluginType: "GEMINI",
+      ideType: 9,        // ANTIGRAVITY
+      platform: platformEnum,
+      pluginType: 2,     // GEMINI
     };
   }
 
@@ -108,7 +117,7 @@ export class AntigravityService {
     const response = await fetch(this.config.loadCodeAssistEndpoint, {
       method: "POST",
       headers: this.getApiHeaders(accessToken),
-      body: JSON.stringify({ metadata: this.getMetadata() }),
+      body: JSON.stringify({ metadata: this.getMetadata(), mode: 1 }),
     });
 
     if (!response.ok) {
@@ -117,7 +126,7 @@ export class AntigravityService {
     }
 
     const data = await response.json();
-    
+
     // Extract project ID
     let projectId = data.cloudaicompanionProject;
     if (typeof projectId === 'object' && projectId !== null && projectId.id) {
@@ -149,6 +158,7 @@ export class AntigravityService {
         tierId,
         metadata: this.getMetadata(),
         cloudaicompanionProject: projectId,
+        mode: 1,
       }),
     });
 
@@ -166,7 +176,7 @@ export class AntigravityService {
   async completeOnboarding(accessToken, projectId, tierId, maxRetries = 10) {
     for (let i = 0; i < maxRetries; i++) {
       const result = await this.onboardUser(accessToken, projectId, tierId);
-      
+
       if (result.done === true) {
         // Extract final project ID from response
         let finalProjectId = projectId;
@@ -301,7 +311,7 @@ export class AntigravityService {
 
       // Load Code Assist to get project ID and tier
       const { projectId, tierId } = await this.loadCodeAssist(tokens.access_token);
-      
+
       if (!projectId) {
         throw new Error("No Google Cloud Project found. Please ensure you have a GCP project with Gemini Code Assist enabled.");
       }
diff --git a/src/lib/oauth/services/gemini.js b/src/lib/oauth/services/gemini.js
index 1830c94a..fd8dca71 100644
--- a/src/lib/oauth/services/gemini.js
+++ b/src/lib/oauth/services/gemini.js
@@ -1,6 +1,6 @@
 import crypto from "crypto";
 import open from "open";
-import { GEMINI_CONFIG } from "../constants/oauth.js";
+import { GEMINI_CONFIG, getOAuthClientMetadata } from "../constants/oauth.js";
 import { getServerCredentials } from "../config/index.js";
 import { startLocalServer } from "../utils/server.js";
 import { spinner as createSpinner } from "../utils/ui.js";
@@ -71,18 +71,11 @@ export class GeminiCLIService {
           "Content-Type": "application/json",
           "User-Agent": "google-api-nodejs-client/9.15.1",
           "X-Goog-Api-Client": "google-cloud-sdk vscode_cloudshelleditor/0.1",
-          "Client-Metadata": JSON.stringify({
-            ideType: "IDE_UNSPECIFIED",
-            platform: "PLATFORM_UNSPECIFIED",
-            pluginType: "GEMINI"
-          })
+          "Client-Metadata": JSON.stringify(getOAuthClientMetadata())
         },
         body: JSON.stringify({
-          metadata: {
-            ideType: "IDE_UNSPECIFIED",
-            platform: "PLATFORM_UNSPECIFIED",
-            pluginType: "GEMINI"
-          }
+          metadata: getOAuthClientMetadata(),
+          mode: 1
         })
       }
     );
@@ -93,7 +86,7 @@ export class GeminiCLIService {
     }
 
     const data = await response.json();
-    
+
     // Extract project ID
     let projectId = "";
     if (typeof data.cloudaicompanionProject === "string") {