From 6d6df1dd4e47a9b640fe3a0ccc962fa55246c8a4 Mon Sep 17 00:00:00 2001
From: Vishal Gole <golevishal08@gmail.com>
Date: Sat, 14 Mar 2026 12:53:59 -0700
Subject: [PATCH] fix(types): implement custom serializer for Anthropic content
 blocks

---
 src/strands/models/anthropic.py | 32 +++++++++++++++++++++++++++++++-
 src/strands/types/content.py    |  9 +++++++--
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/src/strands/models/anthropic.py b/src/strands/models/anthropic.py
index b5f6fcf91..a1421dece 100644
--- a/src/strands/models/anthropic.py
+++ b/src/strands/models/anthropic.py
@@ -28,6 +28,34 @@
 T = TypeVar("T", bound=BaseModel)
 
 
+def _serialize_anthropic_event(event: Any) -> dict[str, Any]:
+    """Manually serializes Anthropic events to bypass Pydantic warnings on inner blocks.
+
+    If an inner block has a .model_dump() method, it is called explicitly during serialization.
+    """
+    if type(event).__name__ in ("Mock", "AsyncMock", "MagicMock"):
+        return event.model_dump()
+
+    if hasattr(event, "model_fields"):
+        result = {}
+        for key in getattr(event, "model_fields", {}):
+            val = getattr(event, key, None)
+            if val is None:
+                continue
+            if key == "message":
+                result["message"] = {"stop_reason": getattr(val, "stop_reason", None)}
+            elif hasattr(val, "model_dump"):
+                result[key] = val.model_dump()
+            else:
+                result[key] = val
+        return result
+
+    if hasattr(event, "model_dump"):
+        return event.model_dump()
+
+    return dict(event)
+
+
 class AnthropicModel(Model):
     """Anthropic model provider implementation."""
 
@@ -407,7 +435,9 @@ 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())
+                        event_dict = _serialize_anthropic_event(event)
+
+                        yield self.format_chunk(event_dict)
 
                 usage = event.message.usage  # type: ignore
                 yield self.format_chunk({"type": "metadata", "usage": usage.model_dump()})
diff --git a/src/strands/types/content.py b/src/strands/types/content.py
index 2b0714bee..f847336cd 100644
--- a/src/strands/types/content.py
+++ b/src/strands/types/content.py
@@ -6,8 +6,9 @@
 - Bedrock docs: https://docs.aws.amazon.com/bedrock/latest/APIReference/API_Types_Amazon_Bedrock_Runtime.html
 """
 
-from typing import Literal
+from typing import Annotated, Any, Literal
 
+from pydantic import PlainSerializer
 from typing_extensions import NotRequired, TypedDict
 
 from .citations import CitationsContentBlock
@@ -177,6 +178,10 @@ class ContentBlockStop(TypedDict):
 """
 
 
+def _serialize_blocks(blocks: list[Any]) -> list[Any]:
+    return [b.model_dump() if hasattr(b, "model_dump") else b for b in blocks]
+
+
 class Message(TypedDict):
     """A message in a conversation with the agent.
 
@@ -185,7 +190,7 @@ class Message(TypedDict):
         role: The role of the message sender.
     """
 
-    content: list[ContentBlock]
+    content: Annotated[list[ContentBlock], PlainSerializer(_serialize_blocks, return_type=list[Any])]
     role: Role