diff --git a/open-sse/services/tokenRefresh.ts b/open-sse/services/tokenRefresh.ts
index 34eac23a74..507e9ff27b 100755
--- a/open-sse/services/tokenRefresh.ts
+++ b/open-sse/services/tokenRefresh.ts
@@ -1063,6 +1063,26 @@ export async function refreshCodexToken(refreshToken, log, proxyConfig: unknown
         return { error: "unrecoverable_refresh_error", code: errorCode };
       }
 
+      // Defense-in-depth (port from decolua/9router#1821): any 401 from OpenAI's
+      // OAuth token endpoint means the refresh credential itself was rejected
+      // (e.g. rotated away, or a payload variant whose code we do not yet
+      // recognize — OpenAI has shipped both `token_expired` and the bare
+      // "Could not validate your token" message). Retrying with the same dead
+      // refresh token will never succeed; surface re-auth instead of looping.
+      // 429 / 5xx remain transient and fall through to the retryable branch.
+      if (response.status === 401) {
+        const code = errorCode || "unauthorized";
+        log?.error?.(
+          "TOKEN_REFRESH",
+          "Codex OAuth token endpoint returned 401. Re-authentication required.",
+          {
+            status: response.status,
+            errorCode: code,
+          }
+        );
+        return { error: "unrecoverable_refresh_error", code };
+      }
+
       log?.error?.("TOKEN_REFRESH", "Failed to refresh Codex token", {
         status: response.status,
         error: errorText,
diff --git a/tests/unit/token-refresh-service.test.ts b/tests/unit/token-refresh-service.test.ts
index 1574a79626..8b2f3e09d0 100644
--- a/tests/unit/token-refresh-service.test.ts
+++ b/tests/unit/token-refresh-service.test.ts
@@ -438,6 +438,37 @@ test("refreshCodexToken recognizes refresh_token_reused responses", async () =>
   );
 });
 
+// Port from decolua/9router#1821 (sacwooky): a 401 from OpenAI's OAuth token
+// endpoint means the refresh credential itself was rejected (e.g. rotated away
+// or a payload whose error code we do not yet recognize). Retrying with the
+// same refresh token will never succeed — surface re-auth, do not loop.
+test("refreshCodexToken treats any 401 from the token endpoint as unrecoverable", async () => {
+  const log = createLog();
+
+  await withMockedFetch(
+    async () =>
+      textResponse(
+        JSON.stringify({
+          error: {
+            // A payload variant whose code/type are NOT in the existing
+            // unrecoverable set — only the 401 status proves the token is dead.
+            message: "Could not validate your token. Please try signing in again.",
+            type: "invalid_request_error",
+          },
+        }),
+        401
+      ),
+    async () => {
+      const result = await refreshCodexToken("codex-refresh", log);
+      assert.equal(
+        result?.error,
+        "unrecoverable_refresh_error",
+        "401 from OpenAI token endpoint must surface re-auth instead of returning null (which triggers retry)"
+      );
+    }
+  );
+});
+
 test("refreshKiroToken uses the AWS OIDC flow when client credentials are present", async () => {
   const log = createLog();
   const calls: any[] = [];