fix(anthropic): normalize ParsedTextBlock to avoid Pydantic serialization warnings

src/strands/models/anthropic.py

@@ -11,6 +11,7 @@
 from typing import Any, TypedDict, TypeVar, cast
 
 import anthropic
+from anthropic.types import TextBlock
 from pydantic import BaseModel
 from typing_extensions import Required, Unpack, override
 
@@ -254,6 +255,32 @@ def _format_tool_choice(tool_choice: ToolChoice | None) -> dict:
         else:
             return {}
 
+    @staticmethod
+    def _normalize_event(event: Any) -> Any:
+        """Normalize Anthropic stream events to avoid Pydantic serialization warnings.
+
+        The Anthropic SDK returns ParsedTextBlock (a TextBlock subclass with an extra
+        parsed_output field) in content_block_start events. Calling model_dump() on those
+        events triggers PydanticSerializationUnexpectedValue warnings because ParsedTextBlock
+        is not in the discriminated union on Message.content.
+
+        This converts any ParsedTextBlock back to a plain TextBlock so the discriminated
+        union matches cleanly and no warnings are emitted.
+        """
+        try:
+            from anthropic.types.parsed_message import ParsedTextBlock
+        except ImportError:
+            return event
+
+        if event.type == "content_block_start" and isinstance(event.content_block, ParsedTextBlock):
+            event.content_block = TextBlock(
+                text=event.content_block.text,
+                type=event.content_block.type,
+                citations=event.content_block.citations,
+            )
+
+        return event
+
     def format_chunk(self, event: dict[str, Any]) -> StreamEvent:
         """Format the Anthropic response events into standardized message chunks.
 
@@ -407,7 +434,7 @@ async def stream(
                 logger.debug("got response from model")
                 async for event in stream:
                     if event.type in AnthropicModel.EVENT_TYPES:
-                        yield self.format_chunk(event.model_dump())
+                        yield self.format_chunk(self._normalize_event(event).model_dump())
 
                 usage = event.message.usage  # type: ignore
                 yield self.format_chunk({"type": "metadata", "usage": usage.model_dump()})

tests/strands/models/test_anthropic.py

@@ -933,3 +933,50 @@ def test_format_request_filters_location_source_document(model, model_id, max_to
     ]
     assert tru_request["messages"] == exp_messages
     assert "Location sources are not supported by Anthropic" in caplog.text
+
+
+def test_normalize_event_converts_parsed_text_block(model):
+    """_normalize_event replaces ParsedTextBlock with TextBlock to avoid Pydantic warnings."""
+    try:
+        from anthropic.types.parsed_message import ParsedTextBlock
+    except ImportError:
+        pytest.skip("ParsedTextBlock not available in this SDK version")
+
+    from anthropic.types import TextBlock
+
+    parsed_block = ParsedTextBlock(type="text", text="hello", citations=None)
+    mock_event = unittest.mock.Mock()
+    mock_event.type = "content_block_start"
+    mock_event.content_block = parsed_block
+
+    result = AnthropicModel._normalize_event(mock_event)
+
+    assert result is mock_event
+    assert isinstance(result.content_block, TextBlock)
+    assert not isinstance(result.content_block, ParsedTextBlock)
+    assert result.content_block.text == "hello"
+
+
+def test_normalize_event_passes_through_text_block(model):
+    """_normalize_event leaves events with a plain TextBlock unchanged."""
+    from anthropic.types import TextBlock
+
+    plain_block = TextBlock(type="text", text="world")
+    mock_event = unittest.mock.Mock()
+    mock_event.type = "content_block_start"
+    mock_event.content_block = plain_block
+
+    result = AnthropicModel._normalize_event(mock_event)
+
+    assert result is mock_event
+    assert result.content_block is plain_block
+
+
+def test_normalize_event_passes_through_non_content_block_start(model):
+    """_normalize_event leaves events with types other than content_block_start unchanged."""
+    mock_event = unittest.mock.Mock()
+    mock_event.type = "message_start"
+
+    result = AnthropicModel._normalize_event(mock_event)
+
+    assert result is mock_event