diff --git a/litellm/litellm_core_utils/get_litellm_params.py b/litellm/litellm_core_utils/get_litellm_params.py
index 57adf23c99e..0925e753e5e 100644
--- a/litellm/litellm_core_utils/get_litellm_params.py
+++ b/litellm/litellm_core_utils/get_litellm_params.py
@@ -109,7 +109,7 @@ def get_litellm_params(
     # the request uses "litellm_metadata" (e.g. /v1/messages from Claude Code).
     _merged_metadata = metadata
     if litellm_metadata and isinstance(litellm_metadata, dict):
-        if not _merged_metadata:
+        if _merged_metadata is None:
             _merged_metadata = dict(litellm_metadata)
         else:
             _merged_metadata = dict(_merged_metadata)  # don't mutate caller's dict
diff --git a/litellm/litellm_core_utils/litellm_logging.py b/litellm/litellm_core_utils/litellm_logging.py
index b47f27da2cd..558e30460fd 100644
--- a/litellm/litellm_core_utils/litellm_logging.py
+++ b/litellm/litellm_core_utils/litellm_logging.py
@@ -608,7 +608,16 @@ class Logging(LiteLLMLoggingBaseClass):
         if "litellm_metadata" in kwargs and isinstance(
             kwargs["litellm_metadata"], dict
         ):
-            base_litellm_params["litellm_metadata"] = kwargs["litellm_metadata"].copy()
+            base_litellm_params["litellm_metadata"] = kwargs["litellm_metadata"]
+            if "metadata" not in base_litellm_params:
+                base_litellm_params["metadata"] = kwargs["litellm_metadata"].copy()
+            else:
+                # Merge litellm_metadata into metadata without overwriting existing
+                # keys so API key fields are visible to callbacks even when
+                # Anthropic's native metadata is present (/v1/messages).
+                for key, value in kwargs["litellm_metadata"].items():
+                    if key not in base_litellm_params["metadata"]:
+                        base_litellm_params["metadata"][key] = value
 
         if litellm_params:
             base_litellm_params.update(litellm_params)
diff --git a/litellm/utils.py b/litellm/utils.py
index 459a366c5cd..acb3c0cc571 100644
--- a/litellm/utils.py
+++ b/litellm/utils.py
@@ -1155,15 +1155,12 @@ def function_setup(  # noqa: PLR0915
             # populate litellm_params["metadata"] so callbacks (e.g. Langfuse) that
             # read API key info from litellm_params["metadata"] see the fields.
             if not litellm_params.get("metadata"):
-                litellm_params["metadata"] = dict(kwargs["litellm_metadata"])
+                litellm_params["metadata"] = kwargs["litellm_metadata"].copy()
             else:
                 # Merge litellm_metadata into metadata without overwriting existing
                 # keys. This ensures API key fields (user_api_key_hash, etc.) are
                 # visible to callbacks even when Anthropic's native metadata field
                 # is present in /v1/messages requests from Claude Code.
-                litellm_params["metadata"] = dict(
-                    litellm_params["metadata"]
-                )  # don't mutate caller's dict
                 for key, value in kwargs["litellm_metadata"].items():
                     if key not in litellm_params["metadata"]:
                         litellm_params["metadata"][key] = value