fix: Span Creation Fails on Messages with Empty Content Field

ddtrace/contrib/internal/anthropic/_streaming.py

@@ -165,6 +165,12 @@ def _on_content_block_delta_chunk(chunk, message):
 
 def _on_content_block_stop_chunk(chunk, message):
     # this is the start to a message.content block (possibly 1 of several content blocks)
+    # Anthropic beta streaming can emit content_block_stop without a corresponding
+    # content_block_start (e.g. empty tool blocks / vendor edge cases). Guard to
+    # avoid IndexError which breaks span construction.
+    if not message.get("content"):
+        return message
+
     content_type = _get_attr(message["content"][-1], "type", "")
     if content_type == "tool_use":
         input_json = _get_attr(message["content"][-1], "input", "{}")

tests/contrib/anthropic/test_anthropic_llmobs.py

@@ -61,6 +61,13 @@
     ],
 )
 class TestLLMObsAnthropic:
+    def test_content_block_stop_without_content_does_not_crash(self):
+        """Regression test for beta streaming: content_block_stop can arrive without any content blocks."""
+        from ddtrace.contrib.internal.anthropic._streaming import _on_content_block_stop_chunk
+
+        message = {"content": []}
+        assert _on_content_block_stop_chunk(chunk=None, message=message) == message
+
     @patch("anthropic._base_client.SyncAPIClient.post")
     def test_completion_proxy(
         self,