diff --git a/src/agents/tracing/traces.py b/src/agents/tracing/traces.py
index a703acf317..adb7ac932a 100644
--- a/src/agents/tracing/traces.py
+++ b/src/agents/tracing/traces.py
@@ -2,6 +2,7 @@
 
 import abc
 import contextvars
+import copy
 import hashlib
 import threading
 from collections import OrderedDict
@@ -178,7 +179,7 @@ def to_json(self, *, include_tracing_api_key: bool = False) -> dict[str, Any] |
         exported = self.export()
         if exported is None:
             return None
-        payload = dict(exported)
+        payload = copy.deepcopy(exported)
         if include_tracing_api_key and self.tracing_api_key:
             payload["tracing_api_key"] = self.tracing_api_key
         return payload
diff --git a/tests/test_trace_json_isolation.py b/tests/test_trace_json_isolation.py
new file mode 100644
index 0000000000..07599d4852
--- /dev/null
+++ b/tests/test_trace_json_isolation.py
@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from agents.tracing.provider import SynchronousMultiTracingProcessor
+from agents.tracing.traces import TraceImpl
+
+
+def test_trace_to_json_detaches_nested_metadata() -> None:
+    trace = TraceImpl(
+        name="workflow",
+        trace_id="trace_test",
+        group_id=None,
+        metadata={"nested": {"value": "original"}},
+        processor=SynchronousMultiTracingProcessor(),
+    )
+
+    payload = trace.to_json()
+    assert payload is not None
+    payload["metadata"]["nested"]["value"] = "changed"
+
+    assert trace.metadata == {"nested": {"value": "original"}}