diff --git a/py/src/braintrust/span_origin.py b/py/src/braintrust/span_origin.py
index fa0237ad..f6b2eaea 100644
--- a/py/src/braintrust/span_origin.py
+++ b/py/src/braintrust/span_origin.py
@@ -1,3 +1,4 @@
+import functools
 import importlib.metadata
 import os
 from typing import Any, TypedDict
@@ -98,6 +99,7 @@ def merge_span_origin_context(
     return merged
 
 
+@functools.cache
 def _sdk_version() -> str:
     try:
         return importlib.metadata.version("braintrust")
diff --git a/py/src/braintrust/test_span_origin.py b/py/src/braintrust/test_span_origin.py
new file mode 100644
index 00000000..6454f5b9
--- /dev/null
+++ b/py/src/braintrust/test_span_origin.py
@@ -0,0 +1,15 @@
+from unittest.mock import patch
+
+from braintrust import span_origin
+
+
+def test_sdk_version_is_cached():
+    span_origin._sdk_version.cache_clear()
+    try:
+        with patch("braintrust.span_origin.importlib.metadata.version", return_value="1.2.3") as version:
+            assert span_origin.merge_span_origin_context({}, "test", None)["span_origin"]["version"] == "1.2.3"
+            assert span_origin.merge_span_origin_context({}, "test", None)["span_origin"]["version"] == "1.2.3"
+
+        version.assert_called_once_with("braintrust")
+    finally:
+        span_origin._sdk_version.cache_clear()