diff --git a/litellm/litellm_core_utils/openai_tool_name_mapping.py b/litellm/litellm_core_utils/openai_tool_name_mapping.py
index dfce305ce87..0c55967ede5 100644
--- a/litellm/litellm_core_utils/openai_tool_name_mapping.py
+++ b/litellm/litellm_core_utils/openai_tool_name_mapping.py
@@ -50,10 +50,23 @@ def should_sanitize_openai_tool_names(litellm_provider: str) -> bool:
     return litellm_provider in _OPENAI_TOOL_NAME_VALIDATION_PROVIDERS
 
 
-def begin_openai_tool_name_mapping_scope() -> None:
-    """Reset both mappings for this completion (call once at the start of completion())."""
-    _CTX.set({})
-    _CTX_REV.set({})
+def begin_openai_tool_name_mapping_scope(*, force_reset: bool = False) -> None:
+    """Initialise (or reset) both mapping dicts for one completion request.
+
+    Idempotent by default: if the ContextVar already holds a dict this is a
+    no-op.  This matters for async streaming where ``acompletion`` calls this
+    function in the *outer* async context before ``contextvars.copy_context()``
+    so that both the executor and the stream consumer share the same dict
+    objects by reference.  The inner ``completion()`` call then sees a non-None
+    dict and skips the reset, preserving the shared reference.
+
+    Pass ``force_reset=True`` only when you explicitly want a clean slate
+    (e.g. in tests).
+    """
+    if force_reset or _CTX.get() is None:
+        _CTX.set({})
+    if force_reset or _CTX_REV.get() is None:
+        _CTX_REV.set({})
 
 
 def _store(sanitized: str, original: str) -> None:
diff --git a/litellm/main.py b/litellm/main.py
index 3e471ac77c7..1cae4e4b3ff 100644
--- a/litellm/main.py
+++ b/litellm/main.py
@@ -611,6 +611,9 @@ async def acompletion(  # noqa: PLR0915
         # Use a partial function to pass your keyword arguments
         func = partial(completion, **completion_kwargs, **kwargs)
 
+        # Initialise the OpenAI tool-name mapping scope in the *outer* async
+        begin_openai_tool_name_mapping_scope()
+
         # Add the context to the function
         ctx = contextvars.copy_context()
         func_with_context = partial(ctx.run, func)
diff --git a/tests/test_litellm/test_utils.py b/tests/test_litellm/test_utils.py
index 601650c3836..692f15d9df9 100644
--- a/tests/test_litellm/test_utils.py
+++ b/tests/test_litellm/test_utils.py
@@ -4032,7 +4032,7 @@ def test_openai_tool_name_mapping_per_request_context():
     )
     from litellm.utils import validate_and_fix_openai_tools
 
-    begin_openai_tool_name_mapping_scope()
+    begin_openai_tool_name_mapping_scope(force_reset=True)
     validate_and_fix_openai_tools(
         tools=[
             {
@@ -4049,7 +4049,8 @@ def test_openai_tool_name_mapping_per_request_context():
         restore_openai_tool_name_for_user("invalid_name_at_index_71")
         == "invalid.name.at.index.71"
     )
-    begin_openai_tool_name_mapping_scope()
+    # Simulate a second request: force_reset=True clears the mapping.
+    begin_openai_tool_name_mapping_scope(force_reset=True)
     assert (
         restore_openai_tool_name_for_user("invalid_name_at_index_71")
         == "invalid_name_at_index_71"
@@ -4066,7 +4067,7 @@ def test_convert_to_model_response_restores_openai_tool_call_names_when_mapped()
     from litellm.types.utils import ModelResponse
     from litellm.utils import validate_and_fix_openai_tools
 
-    begin_openai_tool_name_mapping_scope()
+    begin_openai_tool_name_mapping_scope(force_reset=True)
     validate_and_fix_openai_tools(
         tools=[
             {
@@ -4121,7 +4122,7 @@ def test_tool_choice_function_name_sanitized_with_tools():
     )
     from litellm.utils import validate_and_fix_openai_tools
 
-    begin_openai_tool_name_mapping_scope()
+    begin_openai_tool_name_mapping_scope(force_reset=True)
     validate_and_fix_openai_tools(
         tools=[
             {
@@ -4152,7 +4153,7 @@ def test_tool_choice_function_name_uses_collision_suffix():
     )
     from litellm.utils import validate_and_fix_openai_tools
 
-    begin_openai_tool_name_mapping_scope()
+    begin_openai_tool_name_mapping_scope(force_reset=True)
     validate_and_fix_openai_tools(
         tools=[
             {
@@ -4175,3 +4176,41 @@ def test_tool_choice_function_name_uses_collision_suffix():
     # "a.b" → "a_b"; "a/b" also sanitizes to "a_b" but gets suffix → "a_b_1"
     assert get_sanitized_tool_name("a.b") == "a_b"
     assert get_sanitized_tool_name("a/b") == "a_b_1"
+
+
+def test_begin_scope_is_idempotent_shared_reference():
+    """begin_openai_tool_name_mapping_scope must not replace the dict when already set.
+
+    This simulates the async-streaming path: the outer acompletion() call
+    initialises the scope (sets _CTX = {}), copy_context() copies the
+    reference, and then the inner completion() call must not clobber it with a
+    new empty dict — otherwise mutations from the executor are invisible to the
+    stream consumer in the outer context.
+    """
+    import contextvars
+
+    from litellm.litellm_core_utils.openai_tool_name_mapping import (
+        _CTX,
+        begin_openai_tool_name_mapping_scope,
+        restore_openai_tool_name_for_user,
+        store_openai_tool_name_mapping,
+    )
+
+    # Outer context initialises the scope (simulates acompletion pre-copy_context).
+    begin_openai_tool_name_mapping_scope(force_reset=True)
+    outer_dict = _CTX.get()
+    assert outer_dict is not None
+
+    # Inner context (executor) calls begin_openai_tool_name_mapping_scope again
+    # and then writes a mapping — simulates what completion() does.
+    def inner():
+        begin_openai_tool_name_mapping_scope()  # must be a no-op (no force_reset)
+        inner_dict = _CTX.get()
+        assert inner_dict is outer_dict, "inner call must not replace the shared dict"
+        store_openai_tool_name_mapping("my_tool", "my.tool")
+
+    ctx = contextvars.copy_context()
+    ctx.run(inner)
+
+    # The outer context must see the mapping written by the inner context.
+    assert restore_openai_tool_name_for_user("my_tool") == "my.tool"