From e323ea243a11830677e2015c9390b3912af78457 Mon Sep 17 00:00:00 2001
From: ryan <ryan@berri.ai>
Date: Wed, 28 Oct 2026 08:37:57 +0000
Subject: [PATCH] fix: preserve json mode preamble text

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
---
 litellm/constants.py                                 |  1 +
 litellm/llms/anthropic/chat/transformation.py        |  8 +++++++-
 litellm/llms/bedrock/chat/converse_transformation.py | 11 +++++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/litellm/constants.py b/litellm/constants.py
index 8cc51d0ab5e..8a2e69e84d1 100644
--- a/litellm/constants.py
+++ b/litellm/constants.py
@@ -1633,6 +1633,7 @@ OPENAI_FINISH_REASONS: Final = [
 ]
 HUMANLOOP_PROMPT_CACHE_TTL_SECONDS: Final = get_env_int("HUMANLOOP_PROMPT_CACHE_TTL_SECONDS", 60)  # 1 minute
 RESPONSE_FORMAT_TOOL_NAME = "json_tool_call"  # default tool name used when converting response format to tool call
+JSON_MODE_PREAMBLE_TEXT_KEY: Final = "json_mode_preamble_text"
 
 ########################### Logging Callback Constants ###########################
 AZURE_STORAGE_MSFT_VERSION: Final = "2019-07-07"
diff --git a/litellm/llms/anthropic/chat/transformation.py b/litellm/llms/anthropic/chat/transformation.py
index 92e7c84031c..409fc963553 100644
--- a/litellm/llms/anthropic/chat/transformation.py
+++ b/litellm/llms/anthropic/chat/transformation.py
@@ -21,6 +21,7 @@ from litellm.constants import (
     DEFAULT_REASONING_EFFORT_MEDIUM_THINKING_BUDGET,
     DEFAULT_REASONING_EFFORT_MINIMAL_THINKING_BUDGET,
     DEFAULT_REASONING_EFFORT_XHIGH_THINKING_BUDGET,
+    JSON_MODE_PREAMBLE_TEXT_KEY,
     RESPONSE_FORMAT_TOOL_NAME,
 )
 from litellm.litellm_core_utils.core_helpers import drops_unsupported_params, map_finish_reason
@@ -3056,7 +3057,12 @@ class AnthropicConfig(AnthropicModelInfo, BaseConfig):
                 REFUSAL_STOP_FIELDS.validate_python(completion_response)
             )
             completion_response["stop_reason"] = "stop"
-            if refusal_fields:
+            if text_content and text_content.strip():
+                json_mode_message.provider_specific_fields = {
+                    **refusal_fields,
+                    JSON_MODE_PREAMBLE_TEXT_KEY: text_content,
+                }
+            elif refusal_fields:
                 json_mode_message.provider_specific_fields = dict(refusal_fields)
             if thinking_blocks:
                 json_mode_message.thinking_blocks = thinking_blocks
diff --git a/litellm/llms/bedrock/chat/converse_transformation.py b/litellm/llms/bedrock/chat/converse_transformation.py
index f54c352fd6e..63c6d8a252b 100644
--- a/litellm/llms/bedrock/chat/converse_transformation.py
+++ b/litellm/llms/bedrock/chat/converse_transformation.py
@@ -19,6 +19,7 @@ import litellm
 from litellm._logging import verbose_logger
 from litellm.constants import (
     BEDROCK_MIN_THINKING_BUDGET_TOKENS,
+    JSON_MODE_PREAMBLE_TEXT_KEY,
     RESPONSE_FORMAT_TOOL_NAME,
 )
 from litellm.litellm_core_utils.core_helpers import (
@@ -2676,6 +2677,16 @@ class AmazonConverseConfig(BaseConfig):
             json_mode_content_str: str | None = tools[0]["function"].get("arguments")
             if json_mode_content_str is not None:
                 json_mode_content_str = AmazonConverseConfig._unwrap_bedrock_properties(json_mode_content_str)
+                message_fields: Final = as_str_mapping(chat_completion_message)
+                existing_content: Final = (message_fields or {}).get("content")
+                if isinstance(existing_content, str) and existing_content.strip():
+                    existing_provider_fields: Final = TypeAdapter(dict[str, object]).validate_python(
+                        (message_fields.get("provider_specific_fields") or {}) if message_fields is not None else {}
+                    )
+                    chat_completion_message["provider_specific_fields"] = {  # rebind-ok: response is built in place
+                        **existing_provider_fields,
+                        JSON_MODE_PREAMBLE_TEXT_KEY: existing_content,
+                    }
                 chat_completion_message["content"] = json_mode_content_str
             return None