diff --git a/packages/traceloop-sdk/tests/test_metrics_common_attributes.py b/packages/traceloop-sdk/tests/test_metrics_common_attributes.py
new file mode 100644
index 0000000000..34a6677636
--- /dev/null
+++ b/packages/traceloop-sdk/tests/test_metrics_common_attributes.py
@@ -0,0 +1,54 @@
+import json
+
+from opentelemetry.context import attach, set_value
+from opentelemetry.semconv_ai import SpanAttributes
+
+from traceloop.sdk.tracing.tracing import metrics_common_attributes
+
+
+def test_scalar_association_properties_pass_through():
+    attach(set_value("association_properties", {"user_id": 1, "user_name": "John"}))
+
+    attributes = metrics_common_attributes()
+
+    assert attributes[f"{SpanAttributes.TRACELOOP_ASSOCIATION_PROPERTIES}.user_id"] == 1
+    assert (
+        attributes[f"{SpanAttributes.TRACELOOP_ASSOCIATION_PROPERTIES}.user_name"]
+        == "John"
+    )
+
+
+def test_list_valued_association_property_is_json_encoded():
+    """LangGraph tags spans with list-valued baggage (e.g. langgraph_triggers).
+    Metric attributes must be hashable/scalar, so a raw list here previously
+    crashed the OTel metrics SDK's aggregation and silently dropped every
+    response-side span attribute set after it (gen_ai.output.messages, etc.)."""
+    attach(
+        set_value(
+            "association_properties",
+            {"langgraph_triggers": ["branch:to:resolve_naics"]},
+        )
+    )
+
+    attributes = metrics_common_attributes()
+
+    key = f"{SpanAttributes.TRACELOOP_ASSOCIATION_PROPERTIES}.langgraph_triggers"
+    assert attributes[key] == json.dumps(["branch:to:resolve_naics"])
+    # must be hashable, matching what the OTel metrics SDK requires for its
+    # aggregation key: frozenset(attributes.items())
+    hash(attributes[key])
+
+
+def test_dict_valued_association_property_is_json_encoded():
+    attach(
+        set_value(
+            "association_properties",
+            {"metadata": {"nested": "value"}},
+        )
+    )
+
+    attributes = metrics_common_attributes()
+
+    key = f"{SpanAttributes.TRACELOOP_ASSOCIATION_PROPERTIES}.metadata"
+    assert attributes[key] == json.dumps({"nested": "value"})
+    hash(attributes[key])
diff --git a/packages/traceloop-sdk/traceloop/sdk/tracing/tracing.py b/packages/traceloop-sdk/traceloop/sdk/tracing/tracing.py
index 8808f85eab..a43fa6ee85 100644
--- a/packages/traceloop-sdk/traceloop/sdk/tracing/tracing.py
+++ b/packages/traceloop-sdk/traceloop/sdk/tracing/tracing.py
@@ -1,4 +1,5 @@
 import atexit
+import json
 import logging
 import os
 from urllib.parse import urlparse
@@ -1221,6 +1222,9 @@ def metrics_common_attributes():
     association_properties = get_value("association_properties")
     if association_properties is not None:
         for key, value in association_properties.items():
+            if isinstance(value, (list, dict)):
+                # OTel metric attributes must be scalar/hashable
+                value = json.dumps(value)
             common_attributes[
                 f"{SpanAttributes.TRACELOOP_ASSOCIATION_PROPERTIES}.{key}"
             ] = value