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fix(experiments): preserve run metadata precedence #1756

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fix(experiments): preserve run metadata precedence #1756

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13510b1
fix(experiments): preserve run metadata precedence
marliessophie Jul 13, 2026
1cf26ee
fix(experiments): preserve metadata type guard
marliessophie Jul 13, 2026
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6 changes: 2 additions & 4 deletions langfuse/_client/client.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2877,9 +2877,10 @@ async def _process_experiment_item(
)

final_observation_metadata = {
**(item_metadata if isinstance(item_metadata, dict) else {}),
**(experiment_metadata or {}),
"experiment_name": experiment_name,
"experiment_run_name": experiment_run_name,
**(experiment_metadata or {}),
}
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trace_id = span.trace_id
Expand Down Expand Up @@ -2920,9 +2921,6 @@ async def _process_experiment_item(
{"dataset_id": dataset_id, "dataset_item_id": dataset_item_id}
)

if isinstance(item_metadata, dict):
final_observation_metadata.update(item_metadata)

experiment_id = dataset_run_id or fallback_experiment_id
experiment_item_id = (
dataset_item_id or get_sha256_hash_hex(_serialize(input_data))[:16]
Expand Down
34 changes: 34 additions & 0 deletions tests/unit/test_propagate_attributes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2748,6 +2748,40 @@ def test_experiment_id_is_stable_across_local_items(
assert len(experiment_ids) == 1
assert result.experiment_id == next(iter(experiment_ids))

def test_experiment_run_metadata_overrides_item_metadata(
self, langfuse_client, memory_exporter
):
langfuse_client.run_experiment(
name="Metadata precedence",
run_name="run-name",
data=[
{
"input": "test",
"metadata": {"shared": "item", "item_only": "yes"},
}
],
task=lambda *, item, **kwargs: "result",
metadata={"shared": "run"},
)
langfuse_client.flush()

span = self.get_span_by_name(memory_exporter, "experiment-item-run")
self.verify_span_attribute(
span,
f"{LangfuseOtelSpanAttributes.OBSERVATION_METADATA}.shared",
"run",
)
self.verify_span_attribute(
span,
f"{LangfuseOtelSpanAttributes.OBSERVATION_METADATA}.experiment_run_name",
"run-name",
)
self.verify_span_attribute(
span,
f"{LangfuseOtelSpanAttributes.OBSERVATION_METADATA}.item_only",
"yes",
)

def test_experiment_attributes_propagate_with_dataset(
self, langfuse_client, memory_exporter, monkeypatch
):
Expand Down