fix(cost_calculator): strip duplicated region segment from alias cost keys

litellm/cost_calculator.py

@@ -810,11 +810,8 @@ def _strip_unregistered_leading_segments(model: str, region_name: str | None) ->
     head_len: Final = 2 if region_name is not None and len(segments) > 2 and segments[1] == region_name else 1
     head: Final = "/".join(segments[:head_len])
     tail: Final = segments[head_len:]
-    strippable: Final = next(
-        (index for index, segment in enumerate(tail) if segment in LlmProvidersSet or segment == region_name),
-        len(tail),
-    )
-    candidates: Final = tuple(f"{head}/{'/'.join(tail[start:])}" for start in range(min(strippable, len(tail) - 1) + 1))
+    strippable: Final = next((index for index, segment in enumerate(tail) if segment in LlmProvidersSet), len(tail))
+    candidates: Final = (f"{head}/{'/'.join(tail[start:])}" for start in range(min(strippable, len(tail) - 1) + 1))
     return next((candidate for candidate in candidates if candidate in litellm.model_cost), model)
 
 

tests/test_litellm/test_cost_calculator.py

@@ -3942,6 +3942,34 @@ def test_select_model_name_strips_unregistered_alias_prefix(_local_model_cost_ma
     assert selected == "vertex_ai/claude-opus-5"
 
 
+def test_select_model_name_strips_duplicated_region_segment(_local_model_cost_map):
+    """A "region/model" alias whose leading segment repeats the request's region must
+    resolve to the region-priced cost key instead of keeping the region segment twice."""
+
+    from litellm.cost_calculator import _select_model_name_for_cost_calc
+
+    response = litellm.ModelResponse(
+        id="x",
+        choices=[
+            {
+                "index": 0,
+                "message": {"role": "assistant", "content": "hi"},
+                "finish_reason": "stop",
+            }
+        ],
+        model="us-east-1/anthropic.claude-v2:1",
+    )
+    response._hidden_params = {"region_name": "us-east-1"}
+
+    selected = _select_model_name_for_cost_calc(
+        model=None,
+        completion_response=response,
+        custom_llm_provider="bedrock",
+    )
+
+    assert selected == "bedrock/us-east-1/anthropic.claude-v2:1"
+
+
 def test_completion_cost_nonzero_for_slash_alias_model_name(_local_model_cost_map):
     """End-to-end cost through a "/"-containing alias must price above zero (#38069)."""