LLM analytics trace totalCost excludes $ai_span $ai_total_cost_usd

Summary

LLM Analytics trace-level totalCost currently appears to exclude $ai_total_cost_usd from $ai_span events.

In our traces, custom operations (for example reranking) are captured as $ai_span with valid $ai_total_cost_usd. The span-level UI shows the cost, but the trace header/table totalCost does not include it.

Expected behavior

Trace/session totalCost should include all AI event costs that belong to the trace, including $ai_span events with $ai_total_cost_usd.

Actual behavior

Trace/session totalCost includes only $ai_generation and $ai_embedding costs.

Evidence in code

Current trace queries sum cost only for event IN ('$ai_generation', '$ai_embedding'):

• posthog/hogql_queries/ai/trace_query_runner.py
• posthog/hogql_queries/ai/traces_query_runner.py

Both queries compute total_cost using:

sumIf(toFloat(properties.$ai_total_cost_usd), event IN ('$ai_generation', '$ai_embedding'))

Repro

1. Send one $ai_generation event with $ai_total_cost_usd = 0.058
2. Send one $ai_span event in the same trace with $ai_total_cost_usd = 0.004
3. Open trace in LLM Analytics

Result:

• Span shows 0.004 correctly
• Trace totalCost shows 0.058 instead of 0.062

Notes

This makes trace/session totals under-report costs whenever teams put billable work on $ai_span (rerank/search/tool/API operations) instead of $ai_generation/$ai_embedding.

If this is intentional, could docs explicitly state that trace/session totals only aggregate generation/embedding events?

Start with posthog/hogql_queries/ai/trace_query_runner.py and posthog/hogql_queries/ai/traces_query_runner.py, focusing on the total_cost expressions and their event filters. Verify the trace and session totals against the repro values, including the $ai_span cost, and ensure both queries report the expected aggregate.