From 0e3aad69409352cc4ab6679a4fdf19c2a1b4f789 Mon Sep 17 00:00:00 2001
From: Liz <91279165+lizradway@users.noreply.github.com>
Date: Mon, 29 Jun 2026 15:07:50 -0400
Subject: [PATCH] fix: suppress Pydantic serialization warnings for
 ParsedMessageStopEvent

Use TYPE_CHECKING guard on ParsedMessageStopEvent.message field to
prevent Pydantic from building a serializer schema that expects
ParsedTextBlock[TypeVar] in the content union. At runtime, the
unparameterized ParsedMessage avoids the type mismatch that causes
PydanticSerializationUnexpectedValue warnings on every streamed
response.

This follows the same pattern already used for
ParsedContentBlockStopEvent.content_block in the same file.
---
 src/anthropic/lib/streaming/_types.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/anthropic/lib/streaming/_types.py b/src/anthropic/lib/streaming/_types.py
index 7399e76f4..8e4a1e404 100644
--- a/src/anthropic/lib/streaming/_types.py
+++ b/src/anthropic/lib/streaming/_types.py
@@ -110,7 +110,10 @@ class ContentBlockStopEvent(RawContentBlockStopEvent):
 class ParsedMessageStopEvent(RawMessageStopEvent, GenericModel, Generic[ResponseFormatT]):
     type: Literal["message_stop"]
 
-    message: ParsedMessage[ResponseFormatT]
+    if TYPE_CHECKING:
+        message: ParsedMessage[ResponseFormatT]
+    else:
+        message: ParsedMessage
 
 
 class ParsedContentBlockStopEvent(RawContentBlockStopEvent, GenericModel, Generic[ResponseFormatT]):