> ## Documentation Index
> Fetch the complete documentation index at: https://s2.dev/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Limits

> Check S2 limits for resources, records, throughput, retention, and reconfiguration.

<Note>
  We can increase certain limits if [feedback](mailto:support@s2.dev) suggests they are too restrictive.
</Note>

## Basins

* Basins are unlimited in number for all accounts with a payment method. Free tier accounts are limited to 100.

* Basin names must be globally unique. The name must be between 8 and 48 characters, comprising lowercase letters, numbers and hyphens. It cannot begin or end with a hyphen.

## Streams

* Streams are unlimited in number.

* Stream names can be an arbitrary string up to 512 characters. They may be hierarchically named (e.g. using a delimiter like `/`) for namespacing — you are able to list streams with prefix filtering.

  <Tip>
    Many use cases around lightweight streams find it useful to configure `create stream on append` / `create stream on read` on the basin, and set a `delete on empty` time threshold for the default stream configuration.
  </Tip>

## Records

* Each record may be up to 1 MiB in metered bytes.
* Batches may contain up to 1000 records, and cumulatively total up to 1 MiB in metered bytes.

S2 uses the following formula for metering record size:

```text theme={null}
8 
+ 2 bytes per header
+ size of all header names and values
+ size of the body
```

## Appends

* 100 MiBps per stream.
* 200 batches per second per stream *per client connection*. When exceeded,
  * `Append` requests will receive an HTTP 429.
  * `AppendSession` will experience throttling.

## Reads

Reads are highly scalable on both throughput and concurrency, due to S2's decoupled architecture and read-through caching.

<Note>
  The system is designed to be elastic, but there are bounds to how fast it can scale. The precise limit that will be enforced is TBD.
</Note>

## Retention

Records may stay visible for a brief period after their retention window expires, typically on the order of minutes.

<Note>
  On the free tier, streams can retain data for 28 days or less. If you want a longer (or infinite) retention, add a payment method in the [Dashboard](http://s2.dev/dashboard).
</Note>

## Reconfiguration

**Storage class** changes on an existing stream (i.e. from `Standard` to `Express`, or vice versa) only take effect when a stream has been inactive for up to 10 minutes. This will become a live migration in the future.