---
title: Event batching for the React SDK v4+
slug: feature-experimentation/docs/event-batching-for-the-react-sdk
docTags: 
createdAt: 2026-08-05T20:40:03.000Z
---

The React SDK lets you batch events and includes options to set a maximum batch size and flush interval timeout. The benefit of event batching is less network traffic for the same number of impression and conversion events tracked.

## Minimum SDK version

v4.0.0+

For versions 3.x and earlier, see [React SDK prior to v4](docId\:S_Hk2_qOmrAi1bqUDpdFI).

In v4, event processing is **opt-in**. If no `eventProcessor` is passed to `createInstance`, no events are dispatched. You must explicitly create an event processor using a factory function.

:::hint{type="info"}
**Note**
Event batching works with both out-of-the-box and custom event dispatchers.

The event batching process does not remove any personally identifiable information (PII) from events. You must still ensure that you are not sending any unnecessary PII to Optimizely.
:::

## Configure event batching

Use `createBatchEventProcessor` to create a batch event processor and pass it to `createInstance`. Events are held in a queue until either:

- The number of events reaches the defined `batchSize`.
- The oldest event has been in the queue for longer than the defined `flushInterval`, which is specified in milliseconds.
- A new datafile revision is received.

```javascript
import {
  createInstance,
  createPollingProjectConfigManager,
  createBatchEventProcessor,
} from '@optimizely/react-sdk';

const optimizely = createInstance({
  projectConfigManager: createPollingProjectConfigManager({
    sdkKey: 'YOUR_SDK_KEY',
  }),
  eventProcessor: createBatchEventProcessor({
    batchSize: 100,
    flushInterval: 3000,
  }),
});
```

## Event processor factories

| Factory                                                     | Use case                                       |
| ----------------------------------------------------------- | ---------------------------------------------- |
| `createBatchEventProcessor({ batchSize?, flushInterval? })` | Batches events before dispatching.             |
| `createForwardingEventProcessor()`                          | Forwards each event immediately (no batching). |

The following table defines the batch event processor options:

| Option          | Type   | Default (browser) | Description                                                                                 |
| --------------- | ------ | ----------------- | ------------------------------------------------------------------------------------------- |
| `batchSize`     | number | 10                | Maximum number of events to hold in the queue before flushing.                              |
| `flushInterval` | number | 1000 ms           | Maximum duration in milliseconds that an event can exist in the queue before being flushed. |

:::hint{type="danger"}
**Warning**
The maximum payload size is 3.5 MB. Optimizely rejects requests with a 400 response code, `Bad Request Error`, if the batch payload exceeds this limit.

The most common cause of a large payload size is a high batch size. If your payloads exceed the size limit, try configuring a smaller batch size.
:::

## Disable event dispatching

To disable sending all events to Optimizely's results backend, simply omit the `eventProcessor` parameter when calling `createInstance`. In v4, this is the default behavior — no events are dispatched unless you explicitly opt in.

## Close Optimizely on application exit

If you enable event batching, you **must** call the Close method (`optimizely.close()`) before exiting. This ensures that queued events are flushed when possible to avoid data loss.

For SSR per-request instances, you can set `disposable: true` in `createInstance` so the instance can be garbage collected without explicitly calling `close()`.

:::hint{type="info"}
**Warning**
Because the Optimizely client maintains a buffer of queued events, you must call `close()` on the Optimizely instance before shutting down your application or whenever dereferencing the instance.
:::

On the browser side, `optimizely.close()` is automatically connected to the [pagehide event](https://developer.mozilla.org/en-US/docs/Web/API/Window/pagehide_event), so there is no need to do any manual instrumentation.