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Definition

The session latency test monitors cumulative model latency per session. For each session, Openlayer sums per-trace latency across all turns, then exposes window-level aggregates you can threshold against. No LLM evaluator is involved — it’s a deterministic aggregation.

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Taxonomy

  • Task types: LLM.
  • Availability: and .
  • Evaluation level: session.
  • Computation: deterministic aggregation.

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Why it matters

  • Per-trace latency is the standard monitoring signal, but total latency within a session is what the user actually waits through.
  • A session that accumulates 15 turns × 3 seconds is a materially different user experience from a single 45-second turn — this metric captures the former.

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Available measurements

MeasurementWhat it means
totalLatencySum of per-trace latency across all traces in the window (global, not per-session)
meanLatencyPerSessionMean of per-session latency sums across sessions in the window
medianLatencyPerSessionMedian of per-session latency sums across sessions in the window
Per-session latency is the sum of all trace latencies in that session, not a per-turn average. meanLatencyPerSession is then the mean across sessions of those per-session sums.

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Required columns

  • Session ID: Groups turns belonging to the same conversation.
  • Latency: Per-trace latency (units follow the openlayer_latency column; usually populated automatically by the Openlayer client or via OpenTelemetry).

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Test configuration examples

[
  {
    "name": "Mean session latency below 30s",
    "description": "Alert when the mean cumulative session latency exceeds 30 seconds",
    "type": "performance",
    "subtype": "sessionLatency",
    "thresholds": [
      {
        "insightName": "sessionLatency",
        "measurement": "meanLatencyPerSession",
        "operator": "<=",
        "value": 30000
      }
    ],
    "subpopulationFilters": null,
    "mode": "monitoring",
    "usesProductionData": true,
    "evaluationWindow": 3600,
    "delayWindow": 0
  }
]