# metadata user_id -> user
metadata = anthropic_request.get("metadata")
if isinstance(metadata, dict) and "user_id" in metadata:
    responses_kwargs["user"] = str(metadata["user_id"])[:64]


### Summary

When Claude Code talks to LiteLLM Proxy using the Anthropic `/v1/messages` endpoint and the deployment routes to an **OpenAI Responses API** backend (`openai/...` with `api_base` pointing to a custom gateway), LiteLLM’s `LiteLLMAnthropicToResponsesAPIAdapter.translate_request()` **always** adds a top-level `user` field to the Responses request when the incoming Anthropic request includes `metadata.user_id`.

Some providers (e.g. custom unified gateways) return **400** with a body like `Unsupported parameter: user` for `POST .../v1/responses`.

Setting `litellm_settings.drop_params: true` in the proxy `config.yaml` **does not** prevent this, because the adapter does not check `litellm.drop_params` before setting `responses_kwargs["user"]`. So `drop_params` is effectively ignored on this code path.

### Environment

- LiteLLM: `1.83.11` (uv tool install)
- Flow: `POST /v1/messages?beta=true` (Anthropic) → internal `aresponses` → upstream `https://example.com/v1/responses`

### Steps to reproduce

1. Configure a model in `model_list` that maps Claude client model names to `openai/<model>` with `api_base` set to a gateway whose Responses API rejects the `user` parameter.
2. Ensure `litellm_settings.drop_params: true`.
3. Send Anthropic-format requests that include `metadata.user_id` (typical for Claude Code).
4. Observe upstream **400**: `Unsupported parameter: user`.

### Expected behavior

When `litellm.drop_params` is `True`, LiteLLM should omit the `user` field from the outgoing Responses API payload if the deployment/gateway does not accept it—or at minimum, **respect `drop_params`** in the Anthropic→Responses adapter the same way other call paths document.

Reference: [Drop unsupported params](https://docs.litellm.ai/docs/completion/drop_params) (proxy: `litellm_settings.drop_params`).

### Actual behavior

`responses_kwargs["user"]` is always set from `metadata.user_id` regardless of `litellm.drop_params`.

### Root cause (code location)

File (approximate path in site-packages):

`litellm/llms/anthropic/experimental_pass_through/responses_adapters/transformation.py`

Method: `LiteLLMAnthropicToResponsesAPIAdapter.translate_request`

Current logic (conceptually, near end of method):

```python
# metadata user_id -> user
metadata = anthropic_request.get("metadata")
if isinstance(metadata, dict) and "user_id" in metadata:
    responses_kwargs["user"] = str(metadata["user_id"])[:64]

### Steps to Reproduce

1. 
2. 
3. 


### Relevant log output

```shell