diff --git a/src/openrouter/utils/retries.py b/src/openrouter/utils/retries.py
index ca7b59ef..dd68d1e9 100644
--- a/src/openrouter/utils/retries.py
+++ b/src/openrouter/utils/retries.py
@@ -1,6 +1,7 @@
 """Code generated by Speakeasy (https://speakeasy.com). DO NOT EDIT."""
 
 import asyncio
+import json
 import random
 import time
 from datetime import datetime
@@ -150,6 +151,24 @@ def _parse_retry_after_ms_header(response: httpx.Response) -> Optional[int]:
     return None
 
 
+TRANSIENT_INNER_ERROR_CODES = {408, 429, 500, 502, 503, 504, 524, 529}
+
+
+def _wraps_transient_inner_code(response: httpx.Response) -> bool:
+    """OpenRouter (a middleman) sometimes wraps a transient upstream failure in an HTTP
+    400 whose JSON error.code holds the real status; retry those. Ordinary 400
+    invalid-request responses (including inner error.code == 400) stay non-retryable."""
+    try:
+        body = response.json()
+    except (json.JSONDecodeError, httpx.ResponseNotRead):
+        return False
+    error = body.get("error") if isinstance(body, dict) else None
+    code = error.get("code") if isinstance(error, dict) else None
+    if isinstance(code, str) and code.isdigit():
+        code = int(code)
+    return code in TRANSIENT_INNER_ERROR_CODES
+
+
 def _get_sleep_interval(
     exception: Exception,
     initial_interval: int,
@@ -207,6 +226,12 @@ def do_request() -> httpx.Response:
 
                         if res.status_code == parsed_code:
                             raise TemporaryError(res)
+
+                if res.status_code == 400:
+                    if not res.is_closed:
+                        res.read()
+                    if _wraps_transient_inner_code(res):
+                        raise TemporaryError(res)
             except (httpx.NetworkError, httpx.TimeoutException) as exception:
                 if retries.config.retry_connection_errors:
                     raise
@@ -252,6 +277,12 @@ async def do_request() -> httpx.Response:
 
                         if res.status_code == parsed_code:
                             raise TemporaryError(res)
+
+                if res.status_code == 400:
+                    if not res.is_closed:
+                        await res.aread()
+                    if _wraps_transient_inner_code(res):
+                        raise TemporaryError(res)
             except (httpx.NetworkError, httpx.TimeoutException) as exception:
                 if retries.config.retry_connection_errors:
                     raise
diff --git a/tests/test_retries.py b/tests/test_retries.py
new file mode 100644
index 00000000..a418525c
--- /dev/null
+++ b/tests/test_retries.py
@@ -0,0 +1,93 @@
+import asyncio
+import unittest
+
+import httpx
+
+from openrouter.utils.retries import (
+    BackoffStrategy,
+    RetryConfig,
+    Retries,
+    _wraps_transient_inner_code,
+    retry,
+    retry_async,
+)
+
+
+def response(status_code, json_body=None):
+    request = httpx.Request("POST", "https://openrouter.ai/api/v1/chat/completions")
+    if json_body is None:
+        return httpx.Response(status_code, request=request)
+    return httpx.Response(status_code, json=json_body, request=request)
+
+
+def fast_retries():
+    # Jitter-free, 1ms intervals. Budget is generous so these tests terminate on
+    # success / non-retryable status rather than on the elapsed-time timeout, which
+    # keeps `calls` counts deterministic regardless of CI scheduling overhead.
+    backoff = BackoffStrategy(
+        initial_interval=1, max_interval=1, exponent=1.0, max_elapsed_time=10000, jitter_ms=0
+    )
+    return Retries(RetryConfig("backoff", backoff, retry_connection_errors=True), ["5XX"])
+
+
+class WrapsTransientInnerCodeTests(unittest.TestCase):
+    def test_400_with_transient_inner_code(self):
+        self.assertTrue(_wraps_transient_inner_code(response(400, {"error": {"code": 502}})))
+
+    def test_400_with_string_inner_code(self):
+        self.assertTrue(_wraps_transient_inner_code(response(400, {"error": {"code": "529"}})))
+
+    def test_400_invalid_request_inner_400_not_retried(self):
+        self.assertFalse(_wraps_transient_inner_code(response(400, {"error": {"code": 400}})))
+
+    def test_400_without_inner_code(self):
+        self.assertFalse(_wraps_transient_inner_code(response(400, {"error": {"message": "bad"}})))
+
+    def test_400_non_json_body(self):
+        self.assertFalse(_wraps_transient_inner_code(response(400)))
+
+
+class RetryIntegrationTests(unittest.TestCase):
+    def test_retries_400_wrapping_transient_code_then_succeeds(self):
+        calls = 0
+
+        def func():
+            nonlocal calls
+            calls += 1
+            if calls < 3:
+                return response(400, {"error": {"message": "Provider returned error", "code": 502}})
+            return response(200, {"ok": True})
+
+        result = retry(func, fast_retries())
+        self.assertEqual(result.status_code, 200)
+        self.assertEqual(calls, 3)  # retried twice, then succeeded
+
+    def test_does_not_retry_plain_400(self):
+        calls = 0
+
+        def func():
+            nonlocal calls
+            calls += 1
+            return response(400, {"error": {"message": "logprobs must be 0-5", "code": 400}})
+
+        result = retry(func, fast_retries())
+        self.assertEqual(result.status_code, 400)
+        self.assertEqual(calls, 1)  # not retried
+
+    def test_async_retries_400_wrapping_transient_code_then_succeeds(self):
+        calls = 0
+
+        async def func():
+            nonlocal calls
+            calls += 1
+            if calls < 3:
+                return response(400, {"error": {"code": 503}})
+            return response(200, {"ok": True})
+
+        result = asyncio.run(retry_async(func, fast_retries()))
+        self.assertEqual(result.status_code, 200)
+        self.assertEqual(calls, 3)
+
+
+if __name__ == "__main__":
+    unittest.main()