diff --git a/services/anthropic_service.py b/services/anthropic_service.py
index a3f13cf..3f70b44 100644
--- a/services/anthropic_service.py
+++ b/services/anthropic_service.py
@@ -100,7 +100,7 @@ class AnthropicService:
                 logger.info("[Anthropic] is_available()=False — cost throttled, caller 應 fallback Gemini")
                 return False
         except Exception:
-            pass  # cost_throttle 不可用不阻擋
+            logger.warning("[Anthropic] cost_throttle check failed; continuing as available", exc_info=True)
         return True
 
     def generate(
diff --git a/tests/test_anthropic_service.py b/tests/test_anthropic_service.py
index c705d1b..df152bf 100644
--- a/tests/test_anthropic_service.py
+++ b/tests/test_anthropic_service.py
@@ -18,6 +18,7 @@ from __future__ import annotations
 
 import os
 import sys
+import logging
 from types import SimpleNamespace
 from unittest.mock import MagicMock, patch
 
@@ -82,6 +83,27 @@ def test_is_available_true_when_sdk_ready(mock_sdk):
     assert svc.is_available() is True
 
 
+def test_is_available_logs_cost_throttle_failure(mock_sdk, monkeypatch, caplog):
+    """cost_throttle 檢查故障時仍維持 Claude 可用，但必須留下診斷 log。"""
+    from services.anthropic_service import AnthropicService
+    import services.cost_throttle_service as cost_throttle_service
+
+    def _raise_cost_throttle_error(provider):
+        raise RuntimeError("cost throttle unavailable")
+
+    monkeypatch.setattr(
+        cost_throttle_service,
+        "is_provider_throttled",
+        _raise_cost_throttle_error,
+    )
+    caplog.set_level(logging.WARNING, logger="services.anthropic_service")
+
+    svc = AnthropicService(api_key='sk-ant-test')
+
+    assert svc.is_available() is True
+    assert "cost_throttle check failed" in caplog.text
+
+
 def test_is_available_false_on_import_error(monkeypatch):
     """SDK 未安裝（ImportError）→ is_available() False，不 raise"""
     # 移除 anthropic 模組讓 import 失敗