How to add extra_body in litellm proxy before going to upstream LLM ?

[azidanit]

eventho the client not put the extra_body in their request, I would like to add more extra_body data (in litellm proxy) to the request that goes to LLM upstream

[Ganesh-403]

@azidanit Yes — LiteLLM Proxy provides a supported way to modify the request before it is forwarded to the upstream LLM.

The recommended approach is to use a proxy async_pre_call_hook, which receives the parsed request body as a mutable data dictionary. You can add or modify any request parameters (including extra_body) before LiteLLM routes the request upstream. :contentReference[oaicite:0]{index=0}

For example:

from litellm.integrations.custom_logger import CustomLogger

class MyProxyHook(CustomLogger):
    async def async_pre_call_hook(
        self,
        user_api_key_dict,
        cache,
        data: dict,
        call_type,
    ):
        # Create extra_body if the client didn't send one
        data.setdefault("extra_body", {})

        # Inject your custom provider-specific parameters
        data["extra_body"]["my_custom_flag"] = True
        data["extra_body"]["tenant_id"] = "internal"

        return data

proxy_handler_instance = MyProxyHook()

Then register the callback in your config.yaml:

litellm_settings:
  callbacks: custom_callbacks.proxy_handler_instance

LiteLLM will invoke this hook before making the upstream completion call, so the modified data (including your injected extra_body) is what gets sent to the provider. :contentReference[oaicite:1]{index=1}

One thing to keep in mind is that extra_body is provider-specific. LiteLLM forwards it, but the upstream provider or backend (vLLM, SGLang, Ollama, etc.) must actually recognize the fields you add; otherwise they'll typically be ignored.

Out of curiosity, which upstream backend are you targeting (vLLM, SGLang, Ollama, OpenAI-compatible server, etc.)? Some providers also support provider-specific parameters directly, which may be cleaner than using extra_body.

If this solves your problem, feel free to mark it as the accepted answer so others can find it easily.