diff --git a/litellm/cost_calculator.py b/litellm/cost_calculator.py
index c8892cd26a5..6fecc7fa976 100644
--- a/litellm/cost_calculator.py
+++ b/litellm/cost_calculator.py
@@ -789,6 +789,7 @@ def completion_cost(  # noqa: PLR0915
                         from litellm.llms.recraft.cost_calculator import (
                             cost_calculator as recraft_image_cost_calculator,
                         )
+
                         return recraft_image_cost_calculator(
                             model=model,
                             image_response=completion_response,
@@ -797,6 +798,7 @@ def completion_cost(  # noqa: PLR0915
                         from litellm.llms.gemini.image_generation.cost_calculator import (
                             cost_calculator as gemini_image_cost_calculator,
                         )
+
                         return gemini_image_cost_calculator(
                             model=model,
                             image_response=completion_response,
@@ -867,7 +869,10 @@ def completion_cost(  # noqa: PLR0915
                     from litellm.proxy._experimental.mcp_server.cost_calculator import (
                         MCPCostCalculator,
                     )
-                    return MCPCostCalculator.calculate_mcp_tool_call_cost(litellm_logging_obj=litellm_logging_obj)
+
+                    return MCPCostCalculator.calculate_mcp_tool_call_cost(
+                        litellm_logging_obj=litellm_logging_obj
+                    )
                 # Calculate cost based on prompt_tokens, completion_tokens
                 if (
                     "togethercomputer" in model
@@ -1318,7 +1323,7 @@ def combine_usage_objects(usage_objects: List[Usage]) -> Usage:
                     combined.completion_tokens_details = CompletionTokensDetails()
 
                 # Check what keys exist in the model's completion_tokens_details
-                for attr in dir(usage.completion_tokens_details):
+                for attr in usage.completion_tokens_details.model_fields:
                     if not attr.startswith("_") and not callable(
                         getattr(usage.completion_tokens_details, attr)
                     ):
@@ -1326,7 +1331,8 @@ def combine_usage_objects(usage_objects: List[Usage]) -> Usage:
                             combined.completion_tokens_details, attr, 0
                         )
                         new_val = getattr(usage.completion_tokens_details, attr, 0)
-                        if new_val is not None:
+
+                        if new_val is not None and current_val is not None:
                             setattr(
                                 combined.completion_tokens_details,
                                 attr,
diff --git a/litellm/router.py b/litellm/router.py
index 2673df1504b..ca724006fdf 100644
--- a/litellm/router.py
+++ b/litellm/router.py
@@ -23,6 +23,7 @@
 from typing import (
     TYPE_CHECKING,
     Any,
+    AsyncGenerator,
     Callable,
     Dict,
     List,
@@ -146,7 +147,7 @@
 from litellm.types.utils import GenericBudgetConfigType, LiteLLMBatch
 from litellm.types.utils import ModelInfo
 from litellm.types.utils import ModelInfo as ModelMapInfo
-from litellm.types.utils import StandardLoggingPayload
+from litellm.types.utils import ModelResponseStream, StandardLoggingPayload, Usage
 from litellm.utils import (
     CustomStreamWrapper,
     EmbeddingResponse,
@@ -1092,7 +1093,7 @@ async def _acompletion_streaming_iterator(
         from litellm.exceptions import MidStreamFallbackError
 
         class FallbackStreamWrapper(CustomStreamWrapper):
-            def __init__(self, async_generator):
+            def __init__(self, async_generator: AsyncGenerator):
                 # Copy attributes from the original model_response
                 super().__init__(
                     completion_stream=async_generator,
@@ -1103,7 +1104,7 @@ def __init__(self, async_generator):
                 self._async_generator = async_generator
 
             def __aiter__(self):
-                return self._async_generator
+                return self
 
             async def __anext__(self):
                 return await self._async_generator.__anext__()
@@ -1113,6 +1114,15 @@ async def stream_with_fallbacks():
                 async for item in model_response:
                     yield item
             except MidStreamFallbackError as e:
+                from litellm.main import stream_chunk_builder
+
+                complete_response_object = stream_chunk_builder(
+                    chunks=model_response.chunks
+                )
+                complete_response_object_usage = cast(
+                    Optional[Usage],
+                    getattr(complete_response_object, "usage", None),
+                )
                 try:
                     # Use the router's fallback system
                     model_group = cast(str, initial_kwargs.get("model"))
@@ -1156,6 +1166,37 @@ async def stream_with_fallbacks():
                     # If fallback returns a streaming response, iterate over it
                     if hasattr(fallback_response, "__aiter__"):
                         async for fallback_item in fallback_response:  # type: ignore
+                            if (
+                                fallback_item
+                                and isinstance(fallback_item, ModelResponseStream)
+                                and hasattr(fallback_item, "usage")
+                            ):
+                                from litellm.cost_calculator import (
+                                    BaseTokenUsageProcessor,
+                                )
+
+                                usage = cast(
+                                    Optional[Usage],
+                                    getattr(fallback_item, "usage", None),
+                                )
+                                if usage is not None:
+                                    usage_objects = [usage]
+                                else:
+                                    usage_objects = []
+
+                                if (
+                                    complete_response_object_usage is not None
+                                    and hasattr(complete_response_object_usage, "usage")
+                                    and complete_response_object_usage.usage is not None  # type: ignore
+                                ):
+                                    usage_objects.append(complete_response_object_usage)
+
+                                combined_usage = (
+                                    BaseTokenUsageProcessor.combine_usage_objects(
+                                        usage_objects=usage_objects
+                                    )
+                                )
+                                setattr(fallback_item, "usage", combined_usage)
                             yield fallback_item
                     else:
                         # If fallback returns a non-streaming response, yield None
@@ -1166,7 +1207,7 @@ async def stream_with_fallbacks():
                     verbose_router_logger.error(
                         f"Fallback also failed: {fallback_error}"
                     )
-                    raise e  # Re-raise the original error
+                    raise fallback_error 
 
         return FallbackStreamWrapper(stream_with_fallbacks())