diff --git a/google/genai/_gaos/google_genai.py b/google/genai/_gaos/google_genai.py
index dc9b3e44c..61bf43844 100644
--- a/google/genai/_gaos/google_genai.py
+++ b/google/genai/_gaos/google_genai.py
@@ -128,6 +128,17 @@ def _get_google_genai_security(api_client: Any) -> Optional[Any]:
 _DEFAULT_MAX_INTERVAL_MS = 8000
 _DEFAULT_EXPONENT = 2
 _MAX_ELAPSED_TIME_MS = 30000
+# Align with google.genai._api_client._RETRY_HTTP_STATUS_CODES. Speakeasy
+# operations default to retrying the entire "5XX" class, which incorrectly
+# retries permanent failures such as HTTP 501 Not Implemented (see #2803).
+_DEFAULT_RETRY_HTTP_STATUS_CODES = (
+    '408',  # Request timeout.
+    '429',  # Too many requests.
+    '500',  # Internal server error.
+    '502',  # Bad gateway.
+    '503',  # Service unavailable.
+    '504',  # Gateway timeout.
+)
 
 
 def _translate_retry_config(http_options: Any) -> RetryConfig:
@@ -147,7 +158,7 @@ def _translate_retry_config(http_options: Any) -> RetryConfig:
     max_interval = _DEFAULT_MAX_INTERVAL_MS
     exponent = _DEFAULT_EXPONENT
     jitter_ms = None
-    status_codes_override = None
+    status_codes_override = list(_DEFAULT_RETRY_HTTP_STATUS_CODES)
 
     if options is not None:
         if options.initial_delay is not None:
diff --git a/google/genai/tests/interactions/test_auth.py b/google/genai/tests/interactions/test_auth.py
index c96e7592f..f5c9eed77 100644
--- a/google/genai/tests/interactions/test_auth.py
+++ b/google/genai/tests/interactions/test_auth.py
@@ -83,6 +83,26 @@ def test_interactions_gemini_retry(monkeypatch):
         client.interactions.create(model='gemini-1.5-flash', input='Hello')
         assert mock_send.call_count == 3
 
+
+def test_interactions_delete_does_not_retry_501(monkeypatch):
+    """HTTP 501 Not Implemented is permanent; do not retry like transient 5XX.
+
+    Regression coverage for https://github.com/googleapis/python-genai/issues/2803.
+    """
+    monkeypatch.setenv('GOOGLE_API_KEY', 'test-api-key')
+    client = Client()
+
+    with mock.patch.object(HTTPClient, "send") as mock_send:
+        mock_send.return_value = Response(
+            501,
+            request=Request('DELETE', ''),
+            headers={'content-type': 'application/json'},
+            content='{"error": {"message": "Not Implemented", "code": "not_implemented"}}',
+        )
+        with pytest.raises(Exception):
+            client.interactions.delete(id='test-interaction-id')
+        assert mock_send.call_count == 1
+
 def test_interactions_gemini_extra_headers(monkeypatch):
     monkeypatch.setenv('GOOGLE_API_KEY', 'test-api-key')
     client = Client()
@@ -307,6 +327,24 @@ async def test_async_interactions_gemini_retry(monkeypatch):
         await client.aio.interactions.create(model='gemini-1.5-flash', input='Hello')
         assert mock_send.call_count == 3
 
+
+@pytest.mark.asyncio
+async def test_async_interactions_delete_does_not_retry_501(monkeypatch):
+    """HTTP 501 Not Implemented is permanent; do not retry like transient 5XX."""
+    monkeypatch.setenv('GOOGLE_API_KEY', 'test-api-key')
+    client = Client()
+
+    with mock.patch.object(AsyncHttpxClient, "send") as mock_send:
+        mock_send.return_value = Response(
+            501,
+            request=Request('DELETE', ''),
+            headers={'content-type': 'application/json'},
+            content='{"error": {"message": "Not Implemented", "code": "not_implemented"}}',
+        )
+        with pytest.raises(Exception):
+            await client.aio.interactions.delete(id='test-interaction-id')
+        assert mock_send.call_count == 1
+
 @pytest.mark.asyncio
 async def test_async_interactions_gemini_extra_headers(monkeypatch):
     monkeypatch.setenv('GOOGLE_API_KEY', 'test-api-key')