diff --git a/agent/transports/anthropic.py b/agent/transports/anthropic.py
index 7ffa71a6f..8588ea0b0 100644
--- a/agent/transports/anthropic.py
+++ b/agent/transports/anthropic.py
@@ -87,14 +87,20 @@ class AnthropicTransport(ProviderTransport):
         return normalize_anthropic_response_v2(response, strip_tool_prefix=strip_tool_prefix)
 
     def validate_response(self, response: Any) -> bool:
-        """Check Anthropic response structure is valid."""
+        """Check Anthropic response structure is valid.
+
+        An empty content list is legitimate when ``stop_reason == "end_turn"``
+        — the model's canonical way of signalling "nothing more to add" after
+        a tool turn that already delivered the user-facing text. Treating it
+        as invalid falsely retries a completed response.
+        """
         if response is None:
             return False
         content_blocks = getattr(response, "content", None)
         if not isinstance(content_blocks, list):
             return False
         if not content_blocks:
-            return False
+            return getattr(response, "stop_reason", None) == "end_turn"
         return True
 
     def extract_cache_stats(self, response: Any) -> Optional[Dict[str, int]]:
diff --git a/tests/agent/transports/test_transport.py b/tests/agent/transports/test_transport.py
index b51336d96..75b3a2c70 100644
--- a/tests/agent/transports/test_transport.py
+++ b/tests/agent/transports/test_transport.py
@@ -114,6 +114,14 @@ class TestAnthropicTransport:
         r = SimpleNamespace(content=[])
         assert transport.validate_response(r) is False
 
+    def test_validate_response_empty_content_with_end_turn_is_valid(self, transport):
+        r = SimpleNamespace(content=[], stop_reason="end_turn")
+        assert transport.validate_response(r) is True
+
+    def test_validate_response_empty_content_with_tool_use_is_invalid(self, transport):
+        r = SimpleNamespace(content=[], stop_reason="tool_use")
+        assert transport.validate_response(r) is False
+
     def test_validate_response_valid(self, transport):
         r = SimpleNamespace(content=[SimpleNamespace(type="text", text="hello")])
         assert transport.validate_response(r) is True