diff --git a/litellm/llms/infinity/common_utils.py b/litellm/llms/infinity/common_utils.py
index e23fe4a0d37..3122664b579 100644
--- a/litellm/llms/infinity/common_utils.py
+++ b/litellm/llms/infinity/common_utils.py
@@ -4,7 +4,7 @@ from litellm.llms.base_llm.chat.transformation import BaseLLMException
 
 
 class InfinityError(BaseLLMException):
-    def __init__(self, status_code: int, message: str, headers: dict | httpx.Headers = {}):
+    def __init__(self, status_code: int, message: str, headers: dict | httpx.Headers | None = None):
         self.status_code = status_code
         self.message = message
         self.request = httpx.Request(method="POST", url="https://github.com/michaelfeil/infinity")
diff --git a/tests/test_litellm/llms/infinity/__init__.py b/tests/test_litellm/llms/infinity/__init__.py
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/tests/test_litellm/llms/infinity/test_common_utils.py b/tests/test_litellm/llms/infinity/test_common_utils.py
new file mode 100644
index 00000000000..f9a2c665c92
--- /dev/null
+++ b/tests/test_litellm/llms/infinity/test_common_utils.py
@@ -0,0 +1,69 @@
+"""
+#38909: InfinityError's `headers` parameter defaulted to a mutable `{}`,
+so every InfinityError raised without an explicit `headers=` argument
+(e.g. litellm/llms/infinity/embedding/transformation.py and
+litellm/llms/infinity/rerank/transformation.py) shared the exact same
+dict object. Mutating one instance's `.headers` would silently leak into
+every other default-constructed InfinityError, including ones raised by
+unrelated requests.
+"""
+
+import httpx
+
+from litellm.llms.infinity.common_utils import InfinityError
+
+
+class TestInfinityErrorDoesNotShareDefaultHeaders:
+    def test_default_headers_is_not_a_mutable_shared_dict(self):
+        """The old `headers: dict = {}` default meant every default-constructed
+        InfinityError's `.headers` was literally the same dict object, created
+        once at function-definition time. The fix defaults to `None` instead,
+        so there is nothing shared to mutate."""
+        first = InfinityError(status_code=500, message="first failure")
+
+        assert first.headers is None
+
+    def test_two_default_constructed_errors_do_not_share_headers_identity(self):
+        """Reproduces the shared-default-object bug directly: with the buggy
+        `= {}` default, `first.headers is second.headers` would be True
+        because both point at the one dict created when the function was
+        defined. Guard against ever reintroducing a mutable default here by
+        asserting the default itself is never a dict."""
+        first = InfinityError(status_code=500, message="first failure")
+        second = InfinityError(status_code=502, message="second failure")
+
+        assert not isinstance(first.headers, dict)
+        assert not isinstance(second.headers, dict)
+
+    def test_mutating_a_dict_passed_to_one_instance_does_not_leak_to_another(self):
+        """When a caller *does* pass an explicit headers dict, mutating it
+        must not affect a different, independently default-constructed
+        InfinityError -- this is exactly what happened before the fix,
+        since the mutated object was the shared default itself."""
+        explicit_headers = {"retry-after": "5"}
+        first = InfinityError(status_code=429, message="rate limited", headers=explicit_headers)
+        second = InfinityError(status_code=500, message="unrelated failure")
+
+        first.headers["x-request-id"] = "abc-123"
+
+        assert second.headers is None
+        assert "x-request-id" not in (second.headers or {})
+
+    def test_explicit_headers_argument_is_still_used_by_identity(self):
+        """The fix should not change behavior when a caller *does* pass
+        headers explicitly -- the same object should be used as-is."""
+        supplied = httpx.Headers({"content-type": "application/json"})
+        err = InfinityError(status_code=500, message="failure", headers=supplied)
+
+        assert err.headers is supplied
+
+    def test_call_sites_that_omit_headers_do_not_crash(self):
+        """litellm/llms/infinity/embedding/transformation.py and
+        litellm/llms/infinity/rerank/transformation.py both raise
+        InfinityError without a `headers=` kwarg -- confirm that still
+        works and yields None rather than a stale shared dict."""
+        err = InfinityError(message="raw response text", status_code=500)
+
+        assert err.status_code == 500
+        assert err.message == "raw response text"
+        assert err.headers is None