Fix/tool call anthropic transformation for vllm

[FelipeRodriguesGare]

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Type

🆕 New Feature
🐛 Bug Fix
✅ Test

Changes

Changed tool_calls validation to accept falsy values as well. Hosted_vllm can send the attribute as an empty list (tool_call: []) and this condition was breaking claude code integration with hosted_vllm models. The agent simply did not return any message due to interpreting everything as tool calls without any tool being called.

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2 out of 3 committers have signed the CLA.

✅ yuneng-berri
✅ FelipeRodriguesGare
❌ shin-berri
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[greptile-apps]

Greptile Summary

Fixes a streaming adaptation bug where OpenAI-compatible providers (e.g. hosted vLLM) emit tool_calls: [] on ordinary text chunks, causing the Anthropic adapter to return input_json_delta instead of text_delta and silently drop all streamed text.

• transformation.py: Tightens the tool-call guard from is not None to a truthiness check (if choice.delta.tool_calls:), so an empty list is treated the same as None.
• test_…_transformation.py: Adds a focused mock test verifying both _translate_streaming_openai_chunk_to_anthropic and _translate_streaming_openai_chunk_to_anthropic_content_block return text-type results when tool_calls=[] is present alongside real text content.

Confidence Score: 5/5

Safe to merge — the change is a single-line guard tightening in one streaming helper, with a direct reproduction test, and no impact on existing non-empty tool-call paths.

The fix is minimal and surgical: replacing is not None with a truthiness check on a list that vLLM can return as empty. The companion test directly exercises both affected methods with tool_calls=[] and verifies the correct text_delta output. The parallel guard in _translate_streaming_openai_chunk_to_anthropic_content_block already used len(...) > 0, so this change brings the two helpers into alignment.

No files require special attention.

Important Files Changed

Filename	Overview
litellm/llms/anthropic/experimental_pass_through/adapters/transformation.py	Single-line fix: changes tool_calls is not None to a truthiness check so an empty list from vLLM no longer triggers the input_json_delta path
tests/test_litellm/llms/anthropic/experimental_pass_through/adapters/test_anthropic_experimental_pass_through_adapters_transformation.py	Adds a new mock-only test covering the empty tool_calls case for both streaming translation helpers; no real network calls, no weakened assertions

_{Reviews (1): Last reviewed commit: "fix(anthropic): handle empty streaming t..." | Re-trigger Greptile}

[oss-pr-review-agent-shin]

🤖 litellm-agent: This PR is currently BLOCKED from merge.

Score: 4/5 ❌

Why blocked:

• 1 unresolved reviewer concern (cla-assistant) (unresolved_concern, -1 pts)

Details: Score docked for: 1 unresolved reviewer concern (cla-assistant).

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[codecov]

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[Sameerlite]

LGTM