diff --git a/src/auth/antigravity/fetch.ts b/src/auth/antigravity/fetch.ts
index 4822f07..b003b5b 100644
--- a/src/auth/antigravity/fetch.ts
+++ b/src/auth/antigravity/fetch.ts
@@ -17,16 +17,15 @@
  * Debug logging available via ANTIGRAVITY_DEBUG=1 environment variable.
  */
 
-import { ANTIGRAVITY_ENDPOINT_FALLBACKS, ANTIGRAVITY_DEFAULT_PROJECT_ID } from "./constants"
-import { fetchProjectContext, clearProjectContextCache } from "./project"
-import { isTokenExpired, refreshAccessToken, parseStoredToken, formatTokenForStorage } from "./token"
+import { ANTIGRAVITY_ENDPOINT_FALLBACKS } from "./constants"
+import { fetchProjectContext, clearProjectContextCache, invalidateProjectContextByRefreshToken } from "./project"
+import { isTokenExpired, refreshAccessToken, parseStoredToken, formatTokenForStorage, AntigravityTokenRefreshError } from "./token"
 import { transformRequest } from "./request"
 import { convertRequestBody, hasOpenAIMessages } from "./message-converter"
 import {
   transformResponse,
   transformStreamingResponse,
   isStreamingResponse,
-  extractSignatureFromSsePayload,
 } from "./response"
 import { normalizeToolsForGemini, type OpenAITool } from "./tools"
 import { extractThinkingBlocks, shouldIncludeThinking, transformResponseThinking } from "./thinking"
@@ -391,7 +390,6 @@ export function createAntigravityFetch(
       try {
         const newTokens = await refreshAccessToken(refreshParts.refreshToken, clientId, clientSecret)
 
-        // Update cached tokens
         cachedTokens = {
           type: "antigravity",
           access_token: newTokens.access_token,
@@ -400,10 +398,8 @@ export function createAntigravityFetch(
           timestamp: Date.now(),
         }
 
-        // Clear project context cache on token refresh
         clearProjectContextCache()
 
-        // Format and save new tokens
         const formattedRefresh = formatTokenForStorage(
           newTokens.refresh_token,
           refreshParts.projectId || "",
@@ -418,6 +414,16 @@ export function createAntigravityFetch(
 
         debugLog("Token refreshed successfully")
       } catch (error) {
+        if (error instanceof AntigravityTokenRefreshError) {
+          if (error.isInvalidGrant) {
+            debugLog(`[REFRESH] Token revoked (invalid_grant), clearing caches`)
+            invalidateProjectContextByRefreshToken(refreshParts.refreshToken)
+            clearProjectContextCache()
+          }
+          throw new Error(
+            `Antigravity: Token refresh failed: ${error.description || error.message}${error.code ? ` (${error.code})` : ""}`
+          )
+        }
         throw new Error(
           `Antigravity: Token refresh failed: ${error instanceof Error ? error.message : "Unknown error"}`
         )
@@ -535,11 +541,33 @@ export function createAntigravityFetch(
             debugLog("[401] Token refreshed, retrying request...")
             return executeWithEndpoints()
           } catch (refreshError) {
+            if (refreshError instanceof AntigravityTokenRefreshError) {
+              if (refreshError.isInvalidGrant) {
+                debugLog(`[401] Token revoked (invalid_grant), clearing caches`)
+                invalidateProjectContextByRefreshToken(refreshParts.refreshToken)
+                clearProjectContextCache()
+              }
+              debugLog(`[401] Token refresh failed: ${refreshError.description || refreshError.message}`)
+              return new Response(
+                JSON.stringify({
+                  error: {
+                    message: refreshError.description || refreshError.message,
+                    type: refreshError.isInvalidGrant ? "token_revoked" : "unauthorized",
+                    code: refreshError.code || "token_refresh_failed",
+                  },
+                }),
+                {
+                  status: 401,
+                  statusText: "Unauthorized",
+                  headers: { "Content-Type": "application/json" },
+                }
+              )
+            }
             debugLog(`[401] Token refresh failed: ${refreshError instanceof Error ? refreshError.message : "Unknown error"}`)
             return new Response(
               JSON.stringify({
                 error: {
-                  message: `Token refresh failed: ${refreshError instanceof Error ? refreshError.message : "Unknown error"}`,
+                  message: refreshError instanceof Error ? refreshError.message : "Unknown error",
                   type: "unauthorized",
                   code: "token_refresh_failed",
                 },
diff --git a/src/auth/antigravity/project.ts b/src/auth/antigravity/project.ts
index 150a02c..1490a66 100644
--- a/src/auth/antigravity/project.ts
+++ b/src/auth/antigravity/project.ts
@@ -267,3 +267,8 @@ export function clearProjectContextCache(accessToken?: string): void {
     projectContextCache.clear()
   }
 }
+
+export function invalidateProjectContextByRefreshToken(_refreshToken: string): void {
+  projectContextCache.clear()
+  debugLog(`[invalidateProjectContextByRefreshToken] Cleared all project context cache due to refresh token invalidation`)
+}
diff --git a/src/auth/antigravity/token.ts b/src/auth/antigravity/token.ts
index 8a4f884..f34ed00 100644
--- a/src/auth/antigravity/token.ts
+++ b/src/auth/antigravity/token.ts
@@ -1,8 +1,3 @@
-/**
- * Antigravity token management utilities.
- * Handles token expiration checking, refresh, and storage format parsing.
- */
-
 import {
   ANTIGRAVITY_CLIENT_ID,
   ANTIGRAVITY_CLIENT_SECRET,
@@ -13,33 +8,86 @@ import type {
   AntigravityRefreshParts,
   AntigravityTokenExchangeResult,
   AntigravityTokens,
+  OAuthErrorPayload,
+  ParsedOAuthError,
 } from "./types"
 
-/**
- * Check if the access token is expired.
- * Includes a 60-second safety buffer to refresh before actual expiration.
- *
- * @param tokens - The Antigravity tokens to check
- * @returns true if the token is expired or will expire within the buffer period
- */
-export function isTokenExpired(tokens: AntigravityTokens): boolean {
-  // Calculate when the token expires (timestamp + expires_in in ms)
-  // timestamp is in milliseconds, expires_in is in seconds
-  const expirationTime = tokens.timestamp + tokens.expires_in * 1000
+export class AntigravityTokenRefreshError extends Error {
+  code?: string
+  description?: string
+  status: number
+  statusText: string
+  responseBody?: string
 
-  // Check if current time is past (expiration - buffer)
+  constructor(options: {
+    message: string
+    code?: string
+    description?: string
+    status: number
+    statusText: string
+    responseBody?: string
+  }) {
+    super(options.message)
+    this.name = "AntigravityTokenRefreshError"
+    this.code = options.code
+    this.description = options.description
+    this.status = options.status
+    this.statusText = options.statusText
+    this.responseBody = options.responseBody
+  }
+
+  get isInvalidGrant(): boolean {
+    return this.code === "invalid_grant"
+  }
+
+  get isNetworkError(): boolean {
+    return this.status === 0
+  }
+}
+
+function parseOAuthErrorPayload(text: string | undefined): ParsedOAuthError {
+  if (!text) {
+    return {}
+  }
+
+  try {
+    const payload = JSON.parse(text) as OAuthErrorPayload
+    let code: string | undefined
+
+    if (typeof payload.error === "string") {
+      code = payload.error
+    } else if (payload.error && typeof payload.error === "object") {
+      code = payload.error.status ?? payload.error.code
+    }
+
+    return {
+      code,
+      description: payload.error_description,
+    }
+  } catch {
+    return { description: text }
+  }
+}
+
+export function isTokenExpired(tokens: AntigravityTokens): boolean {
+  const expirationTime = tokens.timestamp + tokens.expires_in * 1000
   return Date.now() >= expirationTime - ANTIGRAVITY_TOKEN_REFRESH_BUFFER_MS
 }
 
-/**
- * Refresh an access token using a refresh token.
- * Exchanges the refresh token for a new access token via Google's OAuth endpoint.
- *
- * @param refreshToken - The refresh token to use
- * @param clientId - Optional custom client ID (defaults to ANTIGRAVITY_CLIENT_ID)
- * @param clientSecret - Optional custom client secret (defaults to ANTIGRAVITY_CLIENT_SECRET)
- * @returns Token exchange result with new access token, or throws on error
- */
+const MAX_REFRESH_RETRIES = 3
+const INITIAL_RETRY_DELAY_MS = 1000
+
+function calculateRetryDelay(attempt: number): number {
+  return Math.min(INITIAL_RETRY_DELAY_MS * Math.pow(2, attempt), 10000)
+}
+
+function isRetryableError(status: number): boolean {
+  if (status === 0) return true
+  if (status === 429) return true
+  if (status >= 500 && status < 600) return true
+  return false
+}
+
 export async function refreshAccessToken(
   refreshToken: string,
   clientId: string = ANTIGRAVITY_CLIENT_ID,
@@ -52,35 +100,81 @@ export async function refreshAccessToken(
     client_secret: clientSecret,
   })
 
-  const response = await fetch(GOOGLE_TOKEN_URL, {
-    method: "POST",
-    headers: {
-      "Content-Type": "application/x-www-form-urlencoded",
-    },
-    body: params,
+  let lastError: AntigravityTokenRefreshError | undefined
+
+  for (let attempt = 0; attempt <= MAX_REFRESH_RETRIES; attempt++) {
+    try {
+      const response = await fetch(GOOGLE_TOKEN_URL, {
+        method: "POST",
+        headers: {
+          "Content-Type": "application/x-www-form-urlencoded",
+        },
+        body: params,
+      })
+
+      if (response.ok) {
+        const data = (await response.json()) as {
+          access_token: string
+          refresh_token?: string
+          expires_in: number
+          token_type: string
+        }
+
+        return {
+          access_token: data.access_token,
+          refresh_token: data.refresh_token || refreshToken,
+          expires_in: data.expires_in,
+          token_type: data.token_type,
+        }
+      }
+
+      const responseBody = await response.text().catch(() => undefined)
+      const parsed = parseOAuthErrorPayload(responseBody)
+
+      lastError = new AntigravityTokenRefreshError({
+        message: parsed.description || `Token refresh failed: ${response.status} ${response.statusText}`,
+        code: parsed.code,
+        description: parsed.description,
+        status: response.status,
+        statusText: response.statusText,
+        responseBody,
+      })
+
+      if (parsed.code === "invalid_grant") {
+        throw lastError
+      }
+
+      if (!isRetryableError(response.status)) {
+        throw lastError
+      }
+
+      if (attempt < MAX_REFRESH_RETRIES) {
+        const delay = calculateRetryDelay(attempt)
+        await new Promise((resolve) => setTimeout(resolve, delay))
+      }
+    } catch (error) {
+      if (error instanceof AntigravityTokenRefreshError) {
+        throw error
+      }
+
+      lastError = new AntigravityTokenRefreshError({
+        message: error instanceof Error ? error.message : "Network error during token refresh",
+        status: 0,
+        statusText: "Network Error",
+      })
+
+      if (attempt < MAX_REFRESH_RETRIES) {
+        const delay = calculateRetryDelay(attempt)
+        await new Promise((resolve) => setTimeout(resolve, delay))
+      }
+    }
+  }
+
+  throw lastError || new AntigravityTokenRefreshError({
+    message: "Token refresh failed after all retries",
+    status: 0,
+    statusText: "Max Retries Exceeded",
   })
-
-  if (!response.ok) {
-    const errorText = await response.text().catch(() => "Unknown error")
-    throw new Error(
-      `Token refresh failed: ${response.status} ${response.statusText} - ${errorText}`
-    )
-  }
-
-  const data = (await response.json()) as {
-    access_token: string
-    refresh_token?: string
-    expires_in: number
-    token_type: string
-  }
-
-  return {
-    access_token: data.access_token,
-    // Google may return a new refresh token, fall back to the original
-    refresh_token: data.refresh_token || refreshToken,
-    expires_in: data.expires_in,
-    token_type: data.token_type,
-  }
 }
 
 /**
diff --git a/src/auth/antigravity/types.ts b/src/auth/antigravity/types.ts
index aec456a..c53e768 100644
--- a/src/auth/antigravity/types.ts
+++ b/src/auth/antigravity/types.ts
@@ -194,3 +194,20 @@ export interface AntigravityRefreshParts {
   projectId?: string
   managedProjectId?: string
 }
+
+/**
+ * OAuth error payload from Google
+ * Google returns errors in multiple formats, this handles all of them
+ */
+export interface OAuthErrorPayload {
+  error?: string | { status?: string; code?: string; message?: string }
+  error_description?: string
+}
+
+/**
+ * Parsed OAuth error with normalized fields
+ */
+export interface ParsedOAuthError {
+  code?: string
+  description?: string
+}
diff --git a/src/hooks/anthropic-auto-compact/parser.ts b/src/hooks/anthropic-auto-compact/parser.ts
index 8d1170f..6d36789 100644
--- a/src/hooks/anthropic-auto-compact/parser.ts
+++ b/src/hooks/anthropic-auto-compact/parser.ts
@@ -26,6 +26,7 @@ const TOKEN_LIMIT_KEYWORDS = [
   "context length",
   "too many tokens",
   "non-empty content",
+  "invalid_request_error",
 ]
 
 const MESSAGE_INDEX_PATTERN = /messages\.(\d+)/
@@ -114,9 +115,10 @@ export function parseAnthropicTokenLimitError(err: unknown): ParsedTokenLimitErr
   if (typeof responseBody === "string") {
     try {
       const jsonPatterns = [
-        /data:\s*(\{[\s\S]*?\})\s*$/m,
-        /(\{"type"\s*:\s*"error"[\s\S]*?\})/,
-        /(\{[\s\S]*?"error"[\s\S]*?\})/,
+        // Greedy match to last } for nested JSON
+        /data:\s*(\{[\s\S]*\})\s*$/m,
+        /(\{"type"\s*:\s*"error"[\s\S]*\})/,
+        /(\{[\s\S]*"error"[\s\S]*\})/,
       ]
 
       for (const pattern of jsonPatterns) {