Google ADK traces may not show cumulative cost at the root span because the current cost aggregation logic in Phoenix only sums costs for direct parent-child relationships, not recursively for all descendants. In complex workflows (like those created by langgraph or Google ADK), this means the root span may not reflect the total cost of the session, and there is no built-in workaround for full cumulative cost aggregation in these cases as of now <https://github.com/Arize-ai/phoenix/issues/8403|see discussion> <https://github.com/Arize-ai/phoenix/issues/8224|see explanation>.
If you need true session-wide cost, you must aggregate costs across all spans in the session manually, as Phoenix does not currently propagate cumulative cost to the root span for graph-based traces <https://github.com/Arize-ai/phoenix/issues/8224|see explanation>.
Would you like more detail on how to implement custom aggregation or on Phoenix's cost tracking logic?
Sources:
- <https://github.com/Arize-ai/phoenix/issues/8403|https://github.com/Arize-ai/phoenix/issues/8403>
- <https://github.com/Arize-ai/phoenix/issues/8224|https://github.com/Arize-ai/phoenix/issues/8224>
