diff --git a/py/src/braintrust/sandbox.py b/py/src/braintrust/sandbox.py
index 606f5365..d416a0f7 100644
--- a/py/src/braintrust/sandbox.py
+++ b/py/src/braintrust/sandbox.py
@@ -107,6 +107,7 @@ def register_sandbox(
                 "provider": sandbox.provider,
                 "snapshot_ref": sandbox.snapshot_ref,
             },
+            "runtime_context": runtime_context,
             "entrypoints": entrypoints,
             "project_id": project_id,
         },