fix(anthropic): capture web_search_tool_result in streaming for multi-turn conversations

[Chesars]

Title

fix(anthropic): capture web_search_tool_result in streaming for multi-turn conversations

Relevant issues

Fixes #17737 for streaming with Anthropic web search tool

Pre-Submission checklist

• I have Added testing in the tests/litellm/ directory, Adding at least 1 test is a hard requirement
• I have added a screenshot of my new test passing locally
• My PR passes all unit tests on make test-unit
• My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🐛 Bug Fix

Changes

This fix addresses two issues with Anthropic web search streaming:

1. Fix trailing {} in tool call arguments

web_search_tool_result blocks have input_json_delta that were emitted as tool calls, with invalid JSON like:

arguments = '{"query": "fun otter facts"}{}{}{}'  ❌

Fix: Added current_content_block_type tracking to only emit tool calls for tool_use and server_tool_use blocks.

2. Capture web_search_tool_result in streaming

Request:

response = completion(
    model="anthropic/claude-sonnet-4-20250514",
    messages=[{"role": "user", "content": "Search the web for weather in Tokyo"}],
    stream=True,
    tools=[{"type": "web_search_20250305", "name": "web_search", "max_uses": 1}]
)

Anthropic sends (streaming SSE):

event: content_block_start
data: {"type": "content_block_start", "content_block": {"type": "server_tool_use", "id": "srvtoolu_01ABC", "name": "web_search"}}

event: content_block_start  
data: {"type": "content_block_start", "content_block": {"type": "web_search_tool_result", "tool_use_id": "srvtoolu_01ABC", "content": [{"url": "...", "title": "...", "encrypted_content": "..."}]}}

Before fix: web_search_tool_result was ignored → provider_specific_fields.web_search_results was empty → multi-turn failed

After fix: LiteLLM returns:

{
  "choices": [{
    "delta": {
      "tool_calls": [{"id": "srvtoolu_01ABC", "function": {"name": "web_search", "arguments": "{...}"}}],
      "provider_specific_fields": {
        "web_search_results": [{"type": "web_search_tool_result", "tool_use_id": "srvtoolu_01ABC", "content": [...]}]
      }
    }
  }]
}

Now multi-turn works because stream_chunk_builder preserves provider_specific_fields .

Tests added

Files changed

• litellm/llms/anthropic/chat/handler.py - Streaming handler fixes
• litellm/main.py - stream_chunk_builder provider_specific_fields handling
• tests/test_litellm/llms/anthropic/chat/test_anthropic_chat_handler.py - 3 new tests

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Project	Deployment	Preview	Comments	Updated (UTC)
litellm	Error			Dec 11, 2025 0:28am