[Feature]: Support OpenRouter's "provider" argument to control/select providers

[paul-gauthier]

The Feature

OpenRouter supports a variety of mechanisms to select which providers you want your requests to hit. This involves passing a provider argument. Currently that causes an error:

import litellm

model = "openrouter/qwen/qwen-2.5-coder-32b-instruct"

messages=[{"role": "user", "content": "say 'hi!'"}]
comp = litellm.completion(
    model=model,
    messages=messages,
    provider=dict(),
)
print(comp)

###

litellm.exceptions.APIError: litellm.APIError: APIError: OpenrouterException - Completions.create() got an unexpected keyword argument 'provider'

Motivation, pitch

This is important because OpenRouter load balances across multiple providers with different prices, context windows, quantizations, etc. It is often important to control which providers are used.

Twitter / LinkedIn details

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