**Description:**

The async_filter_deployments method is an extremely useful hook in the CustomLogger class for filtering deployments before routing, but it's completely undocumented. This makes it difficult for users to discover and implement custom deployment filtering logic.

**Current Situation** The hook exists and is actively used in the router code (litellm/router.py around line ~4835), but:

❌ Not mentioned in the documentation ❌ Not in any examples ❌ Not in the API reference ❌ Difficult to discover without reading source code

**Use Case**

We're using async_filter_deployments to implement dynamic region failover in our LLM proxy. When a region experiences issues, we disable it in our database, and this hook filters out disabled regions from the healthy deployments list before routing occurs.

Example implementation:

``` from litellm.integrations.custom_logger import CustomLogger from typing import List, Optional, Any

class MyCustomHandler(CustomLogger): async def async_filter_deployments( self, model: str, healthy_deployments: List, messages: Optional[List], request_kwargs: Optional[dict] = None, parent_otel_span: Opt…