fix(streaming): add direct type-map fallback for raw dict events (fixes #941)

src/anthropic/lib/streaming/_beta_messages.py

@@ -31,7 +31,23 @@
 from ..._utils._utils import is_given
 from .._parse._response import ResponseFormatT, parse_text
 from ...types.beta.parsed_beta_message import ParsedBetaMessage, ParsedBetaContentBlock
-
+from ...types.beta.beta_raw_message_start_event import BetaRawMessageStartEvent
+from ...types.beta.beta_raw_message_delta_event import BetaRawMessageDeltaEvent
+from ...types.beta.beta_raw_message_stop_event import BetaRawMessageStopEvent
+from ...types.beta.beta_raw_content_block_start_event import BetaRawContentBlockStartEvent
+from ...types.beta.beta_raw_content_block_delta_event import BetaRawContentBlockDeltaEvent
+from ...types.beta.beta_raw_content_block_stop_event import BetaRawContentBlockStopEvent
+
+
+
+_BETA_RAW_EVENT_TYPE_MAP: dict[str, type[BaseModel]] = {
+    "message_start": BetaRawMessageStartEvent,
+    "message_delta": BetaRawMessageDeltaEvent,
+    "message_stop": BetaRawMessageStopEvent,
+    "content_block_start": BetaRawContentBlockStartEvent,
+    "content_block_delta": BetaRawContentBlockDeltaEvent,
+    "content_block_stop": BetaRawContentBlockStopEvent,
+}
 
 class BetaMessageStream(Generic[ResponseFormatT]):
     text_stream: Iterator[str]

src/anthropic/lib/streaming/_messages.py

@@ -28,6 +28,23 @@
 from ..._utils._utils import is_given
 from .._parse._response import ResponseFormatT, parse_text
 from ...types.parsed_message import ParsedMessage, ParsedContentBlock
+from ...types.raw_message_start_event import RawMessageStartEvent
+from ...types.raw_message_delta_event import RawMessageDeltaEvent
+from ...types.raw_message_stop_event import RawMessageStopEvent
+from ...types.raw_content_block_start_event import RawContentBlockStartEvent
+from ...types.raw_content_block_delta_event import RawContentBlockDeltaEvent
+from ...types.raw_content_block_stop_event import RawContentBlockStopEvent
+
+
+
+_RAW_EVENT_TYPE_MAP: dict[str, type[BaseModel]] = {
+    "message_start": RawMessageStartEvent,
+    "message_delta": RawMessageDeltaEvent,
+    "message_stop": RawMessageStopEvent,
+    "content_block_start": RawContentBlockStartEvent,
+    "content_block_delta": RawContentBlockDeltaEvent,
+    "content_block_stop": RawContentBlockStopEvent,
+}
 
 
 class MessageStream(Generic[ResponseFormatT]):
@@ -445,7 +462,19 @@ def accumulate_event(
             ),
         )
         if not isinstance(cast(Any, event), BaseModel):
-            raise TypeError(f"Unexpected event runtime type, after deserialising twice - {event} - {type(event)}")
+            # Union discriminator deserialization silently returned the raw dict in some
+            # environments (e.g. older pydantic versions). Fall back to a direct type-map
+            # lookup using the 'type' field so that well-formed events (including
+            # content_block_delta) are always promoted to the correct BaseModel. See #941.
+            raw = cast(Any, event)
+            if isinstance(raw, dict):
+                event_type = raw.get("type")
+                target_cls = _RAW_EVENT_TYPE_MAP.get(event_type) if isinstance(event_type, str) else None
+                if target_cls is not None:
+                    event = cast(RawMessageStreamEvent, target_cls.model_construct(**raw))
+
+            if not isinstance(cast(Any, event), BaseModel):
+                raise TypeError(f"Unexpected event runtime type, after deserialising twice - {event} - {type(event)}")
 
     if current_snapshot is None:
         if event.type == "message_start":