# Experiment.started

URL: /business/events/Experiment.started · Id: `event:Experiment.started`

> Emitted each time an Experiment is started.

[Experiment.start](/business/nouns/experiment/start) emits `Experiment.started` when it completes on an [Experiment](/business/nouns/experiment).

| Property | Value |
| --- | --- |
| Emitted by | [Experiment.start](/business/nouns/experiment/start) |
| Noun | [Experiment](/business/nouns/experiment) |
| Moves | [Experiment](/business/nouns/experiment) `draft` to `running` |
| Wakes | None. |

### Payload
Each delivery is an [Event](/business/nouns/event) record. `data` holds what [Experiment.start](/business/nouns/experiment/start) returns.

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `name` | `string` | Yes | `Experiment.started`. |
| `at` | `datetime` | Yes | When it happened. |
| `seq` | `integer` | No | Its position in the namespace, one more than the Event before; any seq is a cursor into the history. |
| `data` | `json` | Yes | The Thing as the Action left it. |
| `data.experiment` | [Experiment](/business/nouns/experiment) | Yes | The running Experiment. |
| `data.experiment.variants` | `json` | Yes | The variants and their split. |
| `data.experiment.decision` | `string` | No | One of `ship`, `kill`, or `iterate`. |

### Example
```json
{
  "$id": "https://api.sb/ledgerlark.com/events/event_1",
  "$type": "Event",
  "name": "Experiment.started",
  "at": "2026-10-22T12:00:00Z",
  "data": {
    "experiment": {
      "$id": "https://api.sb/ledgerlark.com/experiments/experiment_1",
      "$type": "Experiment",
      "variants": {},
      "decision": "ship"
    }
  },
  "seq": 1
}
```