diff --git a/.env.example b/.env.example
index 0a222a0..df45908 100644
--- a/.env.example
+++ b/.env.example
@@ -5,3 +5,6 @@ TURSO_AUTH_TOKEN=<your-turso-token>
 
 # Optional: local server port. Defaults to 3003.
 PORT=3003
+
+# Optional: rotate to the next provider account when upstream returns 429.
+KLEIS_RATE_LIMIT_FAILOVER=1
diff --git a/README.md b/README.md
index efe6bd9..3692ff6 100644
--- a/README.md
+++ b/README.md
@@ -45,6 +45,8 @@ ADMIN_TOKEN=replace-with-a-long-random-token
 CRON_SECRET=replace-with-a-long-random-token
 TURSO_CONNECTION_URL=libsql://<your-db>.<region>.turso.io
 TURSO_AUTH_TOKEN=<your-turso-token>
+# Optional: rotate to the next provider account when upstream returns 429.
+KLEIS_RATE_LIMIT_FAILOVER=1
 ```
 
 ```sh
diff --git a/src/domain/providers/provider-service.ts b/src/domain/providers/provider-service.ts
index f477216..1d24c6f 100644
--- a/src/domain/providers/provider-service.ts
+++ b/src/domain/providers/provider-service.ts
@@ -5,8 +5,10 @@ import {
   findProviderAccountsByIds,
   findPrimaryProviderAccount,
   hasActiveProviderAccountRefreshLock,
+  listProviderAccounts,
   recordProviderAccountRefreshFailure,
   releaseProviderAccountRefreshLock,
+  setPrimaryProviderAccount,
   tryAcquireProviderAccountRefreshLock,
   updateProviderAccountTokens,
   upsertProviderAccount,
@@ -335,6 +337,42 @@ const getPrimaryProviderAccount = async (
   return refreshProviderAccount(database, account.id, now);
 };
 
+export const rotateProviderPrimaryAccount = async (
+  database: Database,
+  provider: Provider,
+  currentAccountId: string,
+  now: number
+): Promise<ProviderAccountRecord | null> => {
+  const accounts = (await listProviderAccounts(database))
+    .filter((account) => account.provider === provider)
+    .sort((left, right) => right.createdAt - left.createdAt);
+  const currentIndex = accounts.findIndex(
+    (account) => account.id === currentAccountId
+  );
+  if (currentIndex === -1 || !accounts[currentIndex]?.isPrimary) {
+    return null;
+  }
+
+  const candidates = [
+    ...accounts.slice(currentIndex + 1),
+    ...accounts.slice(0, currentIndex),
+  ];
+
+  for (const account of candidates) {
+    const refreshed =
+      account.expiresAt > now
+        ? account
+        : await refreshProviderAccount(database, account.id, now).catch(
+            () => null
+          );
+    if (refreshed) {
+      return setPrimaryProviderAccount(database, refreshed.id, Date.now());
+    }
+  }
+
+  return null;
+};
+
 export const getRoutableProviderAccount = async (
   database: Database,
   provider: Provider,
diff --git a/src/http/routes/proxy.ts b/src/http/routes/proxy.ts
index 1483aa1..dcee020 100644
--- a/src/http/routes/proxy.ts
+++ b/src/http/routes/proxy.ts
@@ -6,7 +6,10 @@ import {
   recordRequestUsage,
   recordTokenUsage,
 } from "../../db/repositories/request-usage";
-import { getRoutableProviderAccount } from "../../domain/providers/provider-service";
+import {
+  getRoutableProviderAccount,
+  rotateProviderPrimaryAccount,
+} from "../../domain/providers/provider-service";
 import { prepareClaudeProxyRequest } from "../../providers/proxies/claude-proxy";
 import {
   deriveCodexSessionId,
@@ -371,6 +374,16 @@ const proxyRequest = async (
     throw error;
   }
 
+  if (
+    process.env.KLEIS_RATE_LIMIT_FAILOVER === "1" &&
+    upstreamResponse.status === 429 &&
+    !accountScopeIds?.length
+  ) {
+    runInBackground(
+      rotateProviderPrimaryAccount(db, route.provider, account.id, Date.now())
+    );
+  }
+
   let responseToClient = upstreamResponse;
   if (responseTransformer) {
     try {