> ## Documentation Index
> Fetch the complete documentation index at: https://docs.openlayer.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Session duration

> Learn how to use the session duration test to monitor wall-clock session length

## Definition

The session duration test monitors the **wall-clock duration of a session** —
first-turn timestamp to last-turn timestamp. Unlike [Session latency](/tests/catalog/session-latency),
which aggregates per-turn processing time, session duration captures the user-facing
end-to-end experience, including idle gaps between turns. No LLM evaluator is
involved — it's a deterministic aggregation.

## Taxonomy

* **Task types**: LLM.
* **Availability**: <Tooltip tip="Continuously evaluate your models and datasets as you iterate on their versions.">development</Tooltip>
  and <Tooltip tip="Monitor a model in production, measure its health, check for drifts and set up alerts.">monitoring</Tooltip>.
* **Evaluation level**: session.
* **Computation**: deterministic aggregation.

## Why it matters

* Session duration is the cleanest proxy for "time spent by a user with the assistant".
  Comparing duration against goal achievement shows whether users who spend more time
  are getting more value.
* Sudden shifts in duration distribution (longer sessions, flatter distribution) are
  often an early warning for regressions in assistant quality.

## Available measurements

Units follow the timestamp column — typically seconds if `openlayer_prediction_timestamp`
is epoch seconds.

| Measurement             | What it means                                                         |
| ----------------------- | --------------------------------------------------------------------- |
| `meanSessionDuration`   | Mean of per-session wall-clock durations (last-turn − first-turn)     |
| `medianSessionDuration` | Median of per-session wall-clock durations                            |
| `meanTimeBetweenTurns`  | Mean idle gap between consecutive turns, averaged across all sessions |

<Note>
  Sessions with only one turn are excluded from duration calculations — at least
  two timestamps are needed for a delta.
</Note>

## Required columns

* **Session ID**: Groups turns belonging to the same conversation.
* **Timestamp**: Per-trace timestamp, used to compute duration as the delta between
  first and last turn.

## Test configuration examples

<CodeGroup>
  ```json Monitoring theme={null}
  [
    {
      "name": "Mean session duration below 10 min",
      "description": "Alert when average session wall-clock duration exceeds 10 minutes",
      "type": "performance",
      "subtype": "sessionDuration",
      "thresholds": [
        {
          "insightName": "sessionDuration",
          "measurement": "meanSessionDuration",
          "operator": "<=",
          "value": 600
        }
      ],
      "subpopulationFilters": null,
      "mode": "monitoring",
      "usesProductionData": true,
      "evaluationWindow": 3600,
      "delayWindow": 0
    }
  ]
  ```
</CodeGroup>

## Related

* [Session latency](/tests/catalog/session-latency) — per-turn processing time, different signal.
* [Session record count](/tests/catalog/session-record-count) — number of turns, complementary to duration.