From 0adbb24633aa7ba423fd387fcf56117e6b360358 Mon Sep 17 00:00:00 2001
From: Cursor Agent <cursoragent@cursor.com>
Date: Thu, 28 May 2026 07:13:23 +0000
Subject: [PATCH] fix(anthropic-streaming): insert content_block_stop between
 held delta and final message_delta

When the stream exhausts with both `holding_chunk` (a content_block_delta)
and `holding_stop_reason_chunk` (a message_delta) buffered, the after-loop
cleanup previously emitted them back-to-back, producing the invalid
Anthropic SSE sequence `content_block_delta -> message_delta`. Insert a
`content_block_stop` between them in both the sync `__next__` and async
`__anext__` paths so the emitted ordering remains
`content_block_delta -> content_block_stop -> message_delta`.

Co-authored-by: Yassin Kortam <yassin@berri.ai>
---
 .../adapters/streaming_iterator.py            | 28 +++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/litellm/llms/anthropic/experimental_pass_through/adapters/streaming_iterator.py b/litellm/llms/anthropic/experimental_pass_through/adapters/streaming_iterator.py
index 4f3a8b8ffb7..6366e287c3e 100644
--- a/litellm/llms/anthropic/experimental_pass_through/adapters/streaming_iterator.py
+++ b/litellm/llms/anthropic/experimental_pass_through/adapters/streaming_iterator.py
@@ -459,6 +459,20 @@ class AnthropicStreamWrapper(AdapterCompletionStreamWrapper):
                 if self.holding_chunk is not None:
                     self.chunk_queue.append(self.holding_chunk)
                     self.holding_chunk = None
+                    # If a final ``message_delta`` is also held, the
+                    # dangling ``content_block_delta`` must be followed
+                    # by ``content_block_stop`` before the
+                    # ``message_delta`` so the emitted SSE stays in
+                    # valid Anthropic order (content_block_delta ->
+                    # content_block_stop -> message_delta) rather than
+                    # the invalid content_block_delta -> message_delta.
+                    if self.holding_stop_reason_chunk is not None:
+                        self.chunk_queue.append(
+                            {
+                                "type": "content_block_stop",
+                                "index": self.current_content_block_index,
+                            }
+                        )
                 if self.holding_stop_reason_chunk is not None:
                     self.chunk_queue.append(
                         self._augment_message_delta_usage(
@@ -677,6 +691,20 @@ class AnthropicStreamWrapper(AdapterCompletionStreamWrapper):
                 if self.holding_chunk is not None:
                     self.chunk_queue.append(self.holding_chunk)
                     self.holding_chunk = None
+                    # If a final ``message_delta`` is also held, the
+                    # dangling ``content_block_delta`` must be followed
+                    # by ``content_block_stop`` before the
+                    # ``message_delta`` so the emitted SSE stays in
+                    # valid Anthropic order (content_block_delta ->
+                    # content_block_stop -> message_delta) rather than
+                    # the invalid content_block_delta -> message_delta.
+                    if self.holding_stop_reason_chunk is not None:
+                        self.chunk_queue.append(
+                            {
+                                "type": "content_block_stop",
+                                "index": self.current_content_block_index,
+                            }
+                        )
                 if self.holding_stop_reason_chunk is not None:
                     self.chunk_queue.append(
                         self._augment_message_delta_usage(